department of civil enginnering

TRANSPORTATION ENGINEERING I

Department of Civil Enginnering

(B.Tech 4

th semester)

Faculty Name : M.Ankita

CONTENTS

PART – A

UNIT – 1

PRINCIPLES OF TRANSPORTATION ENGINEERING:

Importance of transportation, Different modes of transportation and comparison,

Characteristics of road transport Jayakar committee recommendations, and

implementation – Central Road Fund, Indian Roads Congress, Central Road Research

Institute

04 Hrs

UNIT – 2

HIGHWAY DEVELOPMENT AND PLANNING:

Road types and classification, road patterns, planning surveys, master plan – saturation

system of road planning, phasing road development in India, problems on best

alignment among alternate proposals Salient Features of 3rd and 4th twenty year road

development plans and Policies, Present scenario of road development in India (NHDP

& PMGSY) and in Karnataka (KSHIP & KRDCL) Road development plan - vision

2021.

06 Hrs

UNIT – 3

HIGHWAY ALIGNMENT AND SURVEYS:

Ideal Alignment, Factors affecting the alignment, Engineering surveys-Map study,

Reconnaissance, Preliminary and Final location & detailed survey, Reports and

drawings for new and re-aligned projects

04 Hrs

HIGHWAY GEOMETRIC DESIGN – I:

Importance, Terrain classification, Design speed, Factors affecting geometric design,

Cross sectional elements-Camber- width of pavement- Shoulders-, Width of

formation- Right of way, Typical cross-sections

05 Hrs

UNIT – 4

HIGHWAY GEOMETRIC DESIGN – II:

Sight Distance- Restrictions to sight distance- Stopping sight distance- Overtaking sight

distance- overtaking zones- Examples on SSD and OSD- Sight distance at intersections,

Horizontal alignment-Radius of Curve- Super elevation – Extra widening- Transition

curve and its length, setback distance – Examples, Vertical alignment-Gradient-summit

and valley curves with examples.

07 Hrs

UNIT – 5

PAVEMENT MATERIALS:

Subgrade soil – desirable properties-HRB soil classification-determination of CBR and

modulus of subgrade reaction-Examples on CBR and Modulus of subgrade reaction,

Aggregates- Desirable properties and list of tests, Bituminous materials-Explanation on

Tar, bitumen, cutback and emulsion-List of tests on bituminous materials.

06 Hrs

UNIT – 6

PAVEMENT DESIGN:

Pavement types, component parts of flexible and rigid pavements and their functions,

design factors, ESWL and its determination-Examples, Flexible pavement- Design of

flexible pavements as per IRC;37-2001-Examples, Rigid pavement- Westergaard‟s equations for load and temperature stresses- Examples- Design of slab thickness only as

per IRC:58-2002

06 Hrs

UNIT – 7

PAVEMENT CONSTRUCTION:

Earthwork –cutting-Filling, Preparation of subgrade, Specification and construction of

i) Granular Sub base, ii) WBM Base, iii) WMM base, iv) Bituminous Macadam, v)

Dense Bituminous Macadam vi) Bituminous Concrete, vii) Dry Lean Concrete sub base

and PQC viii) concrete roads

05 Hrs

HIGHWAY DRAINAGE:

Significance and requirements, Surface drainage system and design-

Examples, sub surface drainage system, design of filter materials

03 Hrs UNIT – 8

HIGHWAY ECONOMICS:

Highway user benefits, VOC using charts only-Examples, Economic analysis - annual

cost method-Benefit Cost Ratio method-NPV-IRR methods- Examples, Highway

financing-BOT-BOOT concepts

06 Hrs

4

TEXT BOOKS:

1. Highway Engineering – S K Khanna and C E G Justo, Nem Chand Bros, Roorkee 2. Highway Engineering - L R Kadiyali, Khanna Publishers, New Delhi

3. Transportation Engineering – K P Subramanium, Scitech Publications, Chennai 4. Transportation Engineering – James H Banks, Mc. Graw. Hill Pub. New Delhi

5. Highway Engineeering –R. Sreenivasa Kumar, University Press. Pvt.Ltd. Hyderabad

REFERENCE BOOKS:

1. Relevant IRC Codes

2. Specifications for Roads and Bridges-MoRT&H, IRC, New Delhi. 3. Transportation Engineering – C. Jotin Khisty, B. Kent lal, PHI Learning Pvt Ltd,

New Delhi.

LIST OF CONTENTS

UNIT-1 PRINCIPLES OF TRANSPORTATION ENGINEERING 1

Introduction 09

Importance of Transportation 10

Different Modes of Transportation 12

Characteristics and Comparison of Different Modes 14

Jayakar Committee Recommendations and Implementation 16

Central Research Fund (CRF) 17

Indian Road Congress (IRC) 17

Central Road Research Institute (CRRI) 18

UNIT-2 HIGHWAY DEVELOPMENT AND PLANNING

Introduction 19

Classification of roads 21

Road patterns 22

Planning Surveys 23

Master plan 25

Saturation System 26

Road development Plan 27

UNIT-3 HIGHWAY ALIGNMENT

Alignment 30

Requirements 30

Factors Controlling Alignment 31

UNIT-4 HIGHWAY GEOMETRIC DESIGN 1 & 2

Introduction 33

6

Factors affecting geometric design 33

Camber 35

Width of carriageway 36

Kerbs 36

Road margins 37

Shoulders 37

Parking Lanes 37

Bus- Bays 37

Service roads 38

Footpath 38

Guard Rails 38

Width of Formation 38

Right of way 39

Sight Distance 40

Types of Sight Distance 40

Stopping sight distance 42

Overtaking sight distance 43

Overtaking zones 45

Horizontal curves 46

Analysis of super-elevation 48

Horizontal Transition curves 52

Length of Transition curves 53

Setback Distance 54

Vertical alignment 57

Gradient 58

Summit Curve

Valley curve 61

UNIT-5 PAVEMENT MATERIALS

Introduction 65

Subgrade Soil 65

Desirable Properties 65

Soil Classification 66

Highway research board (HRB) classification of soils 66

California bearing ratio (CBR) test 67

AGGREGATES 73

Tests on Road aggregate 74

BITUMINOUS MATERIALS 75

Types of bituminous materials 75

Tests on Bitumen 76

Bituminous Emulsion 78

BITUMINOUS PAVING MIXES 81

UNIT-6 INTRODUCTION TO PAVEMENT DESIGN

Requirements of a pavement 82

Types of pavements 82

Flexible Pavements 82

Rigid Pavements 83

Types of Rigid pavements 84

Factors affecting Pavement design 85

IRC method of Design of Flexible Pavements 89

Rigid pavement Design 92

8

Wheel load Stresses- Westergaard‟s equation 92

UNIT-7 HIGHWAY CONSTRUCTION

Introduction 95

Earthwork 95

Construction of Earth Roads 99

Construction of Gravel Roads 100

Construction of WBM Roads 101

Construction of Bituminous Pavements 105

Construction procedure for Bituminous Concrete 110

HIGHWAY DRAINAGE 117

Introduction 117

Importance of Highway Drainage 117

UNIT-8 HIGHWAY ECONOMICS & FINANCE

Introduction 122

Highway User benefits 122

Annual Highway Cost 136

HIGHWAY FINANCE 128

Highway financing in India 128

9

UNIT-I PRINCIPLES OF TRANSPORTATION

ENGINEERING-I

INTRODUCTION

Basic Definition: A facility consisting of the means and equipment necessary for the

movement of passengers or goods. At its most basic, the term “transportation system”

is used to refer to the equipment and logistics of transporting passengers and goods. It

covers movement by all forms of transport, from cars and buses to boats, aircraft and

even space travel. Transportation systems are employed in troop movement logistics

and planning, as well as in running the local school bus service.

Function: The purpose of a transportation system is to coordinate the movement of

people, goods and vehicles in order to utilize routes most efficiently. When

implemented, transportation systems seek to reduce transport costs and improve

delivery times through effective timetabling and route management. Periodic re-

evaluations and the development of alternative routes allow for timely changes to the

transportation system in order to maintain efficiency.

Features: A standard transportation system will usually feature multiple timetables

designed to inform the user of where each vehicle in the fleet is expected to be at any

given point in time. These timetables are developed alongside an array of route plans

designed to coordinate vehicle movements in a way that prevents bottlenecks in any

one location.

Benefits: The main benefit of implementing a transportation system is delivery of

goods and personnel to their destinations in a timely manner. This in turn increases the

efficiency of vehicle use, as the same vehicle can be used for “multi-drop” jobs, such

as bus services or home delivery networks, far more effectively when their routes are

planned in advance rather than being generated “on the fly.”

Size: Transportation systems are developed in a wide variety of sizes. Local transport

networks spanning the bus network for a city and its suburbs are common, as are

Smartworld.asia 10

Transportation Engineering 1 10CV56

country-wide delivery networks for haulage firms. Airlines use international

transportation systems to coordinate their flights. The larger the distance being covered,

the more effective the use of vehicles when a transportation system is used.

IMPORTANCE OF TRANSPORTATION

The world that we live in now will most likely be impossible had it not been for

innovations in transportation. There would not have been any great infrastructure,

industrialization, or massive production, if transportation was incompetent. Life would

not have kept up with the fast changing times if there were no huge trucks, bulldozers,

trailers, cargo ships, or large aircrafts to carry them to different places. In other words,

the global society would not have experienced comfort and convenience had it not been

for advancements in the transportation sector. Today, humanity has technology to thank

for all the wonderful things that it currently enjoys now.

Transportation is vital for the economic development of any region since every

commodity produced whether it is food, clothing, industrial products or medicine needs

transport at all stages from production to distribution. In the production stage

transportation is required for carrying raw materials like seeds, manure, coal, steel etc.

In the distribution stage transportation is required from the production centre‟s viz;

farms and factories to the marketing centres and later to the retailers and the consumers

for distribution.

The transportation has lots of advantages and even disadvantages. The more

focus is on advantages as we cannot think about the life without transportation. The

importance of transportation may include:

Availability of raw materials: Transportation helps in carrying the raw

materials from one place to another place. Initially raw materials are made at one

place and are being transported to another place for processing and for

manufacturing goods.

Availability of goods to the customer: The goods are being transported from

Smartworld.asia 11


one place to another place. These goods which are produced at one place are

transported

to other distant places for their usage. It flexibly moves the goods from one

place to another place.

Enhances the Standard Of Living: It improves the standard of living. As the

transportation of each and every good is being done then the productivity

increases which results in the reduced or the effective costs. Because of

reduction in the cost they can use different commodities for different purposes

and can lead a secure life.

Helps a lot during the emergencies and even during natural disasters:

Transportation helps during the natural disturbances. It helps in quick moving

from one place to another place and supplies the required operations.

Helps for the employment: Transportation provides employment for many

people as drivers, captains, conductors, cabin crew and even the people are used

for the construction of different types of transportation vehicles. And even by the

use of transportation the remote people are being employed with the access to

the urban facilities and the opportunities.

Helps in mobility of the laborers: Many people are traveling to other countries

on their employment basis. Transportation plays an important role in such cases.

Helps for bringing nations together: Transportation on the whole is used for

globalization i.e. it brings nations together and it creates awareness about the

cultural activities and even about the industries and helps a lot for importing and

exporting of different goods.

These above are some of the necessities which make us to use transportation.

The importance and adequacy of transportation system of a country indicates its

economic and social development.

Economic Activity: Two important factors well known in economic activity are:

Production or supply and

Smartworld.asia 12


Consumption for human wants or demand.

Social Effects: The various social effects of transportation may be further classified into: Sectionalism and transportation

Concentration of population into urban

area Aspect of safety, law and order.

DIFFERENT MODES OF TRANSPORTATION

Three basic modes of transport are by land, water and air. Land has given

development of road and rail transport. Water and air have developed waterways and

airways respectively. Apart from these major modes of transportation, other modes

include pipelines, elevators, belt conveyors, cable cars, aerial ropeways and monorails.

Pipe lines are used for the transportation of water, other fluids and even solid particles

The four major modes of transportation are:

Roadways or highways

Railways

Airways

Waterways.

Airways:

The transportation by air is the fastest among the four modes.

Air also provides more comfort apart from saving in transportation time for the

passengers and the goods between the airports.

Waterways:

Transportation by water is the slowest among the four modes.

This mode needs minimum energy to haul load through unit distance The transportation by water is possible between the ports on the sea routes or along

Smartworld.asia 13


the rivers or canals where inland transportation facilities are available.

Railways:

The transportation along the railway track could be advantageous by railways

between the stations both for the passengers and goods, particularly for longer

distances.

The energy requirement to haul unit load through unit distance by the railway is

only a fraction (one fourth to one sixth) of the required by road.

Hence, full advantage of this mode of transportation should be taken for the

transportation of bulk goods along land where the railway facilities are

available.

Roadways:

The transportation by road is the only mode which could give maximum service

to one and all.

The road or highways not only include the modern highway system but also the

city streets, feeder roads and village roads, catering for a wide-range of road

vehicles and the pedestrians.

This mode has also maximum flexibility for travel with reference to route,

direction, time and speed of travel etc. through any mode of road vehicle.

It is possible to provide door to door service by road transport.

The other three modes (railways; water ways; airways) has to depend on the

roadway for the service.

Ultimately, road network is therefore needed not only to serve as feeder system

for other modes of transportation and to supplement them, but also to provide

independent facility for road travel by a well planned network of roads

throughout

Smartworld.asia 14


CHARACTERISTICS AND COMPARISON OF DIFFERENT MODES

It is accepted that the fact road transport is the nearest to the people. The

passengers and goods have to be first transported by road before reaching a railway

station or an airport. It is seen that road network alone could serve the remotest villages

of the vast country like occurs.

The various characteristics (advantages) and disadvantages of different mode of

transport are briefly listed here:

Roadways:

Advantages:

Flexibility: It offers complete freedom to the road users.

It requires relatively smaller investments and cheaper in construction with respect to

other modes.

It serves the whole community alike the other modes.

For short distance travel it saves time.

These are used by various types of vehicles.

Disadvantages:

Speed is related to accidents and more accidents results due to higher speed.

Not suitable for long distance travel

Power required per tonne is more.

Railways:

Advantages:

Can transport heavy loads of goods at higher speed

Power required per tonne is less compared to roadways

Chances of accidents are less.

Smartworld.asia 15


Disadvantages:

Entry and exist points are fixed

Requires controlling system and no freedom of movement

Establishment and maintenance cost is higher.

Waterways:

Advantages:

Cheapest: Cost per tonne is lowest

Possess highest load carrying capacity

Leads to the development of the industries.

Disadvantages:

Slow in operation and consumes more time

Depends on weather condition

Chances of attack by other countries on naval ships are more.

Ocean tides affect the loading and unloading operation

The route is circuitous.

Airways:

Advantages:

It has highest speed

Intercontinental travel is possible

Journey is continuous over land and water

Disadvantages:

Highest operating cost (cost/tonne is more)

Load carrying capacity is lowest

Smartworld.asia 16


Depends on weather condition

Should follow the flight rules.

JAYAKAR COMMITTEE RECOMMENDATIONS AND IMPLEMENTATION

RECOMMENDATIONS: Over a period after the First World War, motor vehicles

using the roads increased and this demanded a better road network which can carry

mixed traffic conditions. The existing roads when not capable to withstand the mixed

traffic conditions. For the improvement of roads in India government of India appointed

Mr. Jayakar Committee to study the situations and to recommend suitable measures for

road improvement in 1927 and a report was submitted in 1928 with following

recommendations:

Road development in the country should be considered as a national interest. As

the provincial and local government do not have the financial and technical

capacity for road development.

Extra tax to be levied from the road users as fund to develop road.

A Semi-official technical body has to be formed to collect and pool technical

knowhow from various parts of the country and to act as an advisory body on

various aspects of the roads.

A research organization should be instituted at National level to carry out research and

development work and should be available for consultation. IMPLEMENTATIONS:

Majority of the recommendations were accepted by the government

implemented by Jayakar Committee.

Some of the technical bodies were formed such as,

• Central Road Fund (CRF) in 1929

Smartworld.asia 17


• Indian Road Congress (IRC) in 1934

• Central Road Research Institute (CRRI) in 1950.

Central Research Fund (CRF):

Central Research Fund (CRF) was formed on 1st

March 1929

The consumers of petrol were charged an extra levy of 2.64 paisa/litre of petrol

to buildup this road development fund.

From the fund collected 20 percent of the annual revenue is to be retained as

meeting expenses on the administration of the road fund, road experiments and

research on road and bridge projects of special importance.

The balance 80 percent of the fund to be allotted by the Central Government to

the various states based on actual petrol consumption or revenue collected

The accounts of the CRF are maintained by the Accountant General of Central

Revenues.

The control of the expenditure is exercised by the Roads Wings of Ministry of

Transport.

Indian Road Congress (IRC):

It s a semi -official technical body formed in 1934.

It was formed to recommend standard specifications.

It was constituted to provide a forum of regular technical pooling of experience

and ideas on all matters affecting the planning, construction and maintenance of roads

in India.

IRC has played an important role in the formulation of the 20-year road

development plans in India.

Now, it has become an active body of national importance controlling

Smartworld.asia 18


specifications, guidelines and other special publications on various aspect of Highway

Engineering.

Central Road Research Institute (CRRI):

CRRI was formed in the year 1950 at New Delhi

It was formed for research in various aspect of highway engineering

It is one of the National laboratories of the Council of Scientific and Industrial

Research.

This institute is mainly engaged in applied research and offers technical advice to

state governments and the industry on various problems concerning roads.

Smartworld.asia 19


UNIT-2 HIGHWAY DEVELOPMENT AND PLANNING

INTRODUCTION `

Highway design is only one element in the overall highway development

process. Historically, detailed design occurs in the middle of the process, linking the

preceding phases of planning and project development with the subsequent phases of

right-of-way acquisition, construction, and maintenance. While these are distinct

activities, there is considerable overlap in terms of coordination among the various

disciplines that work together, including designers, throughout the process.

It is during the first three stages, planning, project development, and design, that

designers and communities, working together, can have the greatest impact on the final

design features of the project. In fact, the flexibility available for highway design during

the detailed design phase is limited a great deal by the decisions made at the earlier

stages of planning and project development. This Guide begins with a description of the

overall highway planning and development process to illustrate when these decisions are

made and how they affect the ultimate design of a facility

Meaning of Highway and Road:

Road: A road is a thoroughfare, route or way on land between two places, which

typically has been paved or otherwise improved to allow travel by some conveyance,

including a horse, cart, or motor vehicle.

Highway: A highway is a public road, especially a major road connecting two or more

destinations. Any interconnected set of highways can be variously referred to as a

"highway system", a "highway network", or a "highway transportation system". Each

country has its own national highway system.

Smartworld.asia 20


TYPES OF ROAD:

Basically, different types of roads can be classified into two categories namely,

All-weather roads

and

Fair-weather roads.

All-weather roads: These roads are negotiable during all weather, except at major

rivercrossings where interruption of traffic is permissible upto a certain limit extent, the

road pavement should be negotiable during all weathers.

Fair-weather roads: On these roads the traffic may be interrupted during monsoon

season atcauseways where streams may overflow across the roads.

CLASSIFICATION OF ROADS:

Roads are classified based on various aspects namely,

1) Based on the carriage way,

Paved Roads: These roads are provided with a hard pavement course which

should be atleast a water bound macadam (WBM) layer.

Unpaved Roads: These roads are not provided with a hard pavement course of

atleast a WBM layer. Thus earth roads and gravel roads may be called as

unpaved roads.

2) Based on Surface pavement provided,

Surface Roads: These roads are provided with a bituminous or cement concrete

surfacing.

Unsurfaced Roads: These are not provided with bituminous or cement concrete

surfacing.

Roads which are provided with bituminous surfacing are called as black toped

roads and that of concrete are referred to as concrete roads respectively.

Smartworld.asia 21


3) Based on Traffic Volume:

Heavy

Medim

Light traffic roads.

4) Based on Load transported or

tonnage: Class-I or Class-A Class-II orClassB.

5) Based on location and Function:

National Highways (NH): The NH connects the capital cities of the states and

the capital cities to the port. The roads connecting the neighbouring countries

are also called as NH. The NH are atleast 2 lanes of traffic about 7.5m d wide.

The NH are having concrete or bituminous surfacing.

State Highways (SH): SH are the main roads within the state and connect

important towns and cities of state. The width of state highways is generally

7.5m.

Major District Roads (MDR): These roads connect the areas of production and

markets with either a SH or railway. The MDR should have atleast metalled

single lane carriage way (i.e., 3.8m) wide. The roads carry mixed traffic.

Other District Roads (ODR): these roads connect the village to other village or

the nearest district road, with ghat, river etc. these roads have a single lane and

carry mixed traffic.

Village Roads (VR): these roads, like other district roads, connect the village or

village or nearby district road. The roads carry mixed traffic.

6) Modified Classification of Road system by Third Road Development Plan:

Primary System (Expressways and National Highways)

Secondary System (State Highways and Major District

Roads) Tertiary System (Other District Roads and Village

Roads).

Smartworld.asia 22


7) Based on Urban Roads:

Arterial roads

Sub-arterialroads

Collector Streets

Local Streets

Arterial and Sub-arterial roads are primarily for through traffic on a

continuous route, but sub-arterials have a lower level of traffic mobility than the

arterials.

Collector streets provide access to arterial streets and they collect and distribute

traffic from and to local streets which provide access to abutting property.

ROAD PATTERNS:

There are various types of road patterns and each pattern has its own advantages

and limitations. The choice of the road pattern depends upon the various factors

such as:

Locality

Layout of the different towns, villages, industrial and production centres.

Planning Engineer.

The various road patterns may be classified as follows:

Rectangular or block pattern: In this, entire area is divided into rectangular

segments having a common central business and marketing area. This area has

all the services located in the central place. This pattern is not convenient or safe

from traffic operation point of view and it results into more number of accidents

at intersections. Eg: Chandigarh city.

Radial or star and block pattern: In this, roads radially emerge from the

central business area in all directions and between two built-up areas will be

there. The main advantage in this, central place is easy accessible from all the

directions. Eg: Nagpur

Radial or star and circular pattern: In this roads radiate in all the directions

and also circular ring roads are provided.

Smartworld.asia 23


Advantages: Traffic will not touch the heart of the city and it flows radially and

reaches the other radial road and thereby reducing the congestion in the centre of

the city. This ring road system is well suited for big cities where traffic problems

are more in the heart of the city. Eg: Connaught place in New Delhi.

Radial or star and grid pattern: It is very much similar to star and the circular

pattern expects the radial roads are connected by grids. In this pattern a grid is

formed around the central point which is a business centre. Eg: Nagpur road

plan.

Hexagonal pattern: In this entire zone of planning is divided into hexagonal

zones having separate marketing zone and central services surrounded by

hexagonal pattern of roads. Each hexagonal element is independent. At each

corner of hexagon three roads meet.

Minimum travel pattern: In this type, city is divided into number of nodal

points around a central portion by forming sectors. And each sector is divided

again in such a way that from each of the nodal centre, the distance to the central

place is minimum.

PLANNING SURVEYS:

Prior to the development of highways planning is required for any

engineering works, which is a basic requirement for a new project or for an

expansion. In all developing countries like India where, the resources are limited

and requirement is high then planning provides better utilization of funds in a

system.

Objective of Planning surveys:

Workout, the financial system and recommended changes in tax arrangements

and budget procedures, provide efficient, safe economics, comfortable and

speedy movement for goods and people.

Plan a road network for efficient traffic operation at minimum cost.

Plan for future requirements and improvements of roads in view of

developments and social needs.

Fix up datawise priorities for development of each road link based on their utilities.

Smartworld.asia 24


The planning surveys consist of the following studies:

Economic Studies: This study consists the following details:

Population and its distribution

Trend of population growth

Age and land products

Existing facilities

Per Capita income.

Financial Studies: This study involves collecting the details such as:

Sources of income

Living Standards

Resources from local levels

Factor trends in financial.

Traffic or road use studies: In this details collected are:

Traffic Volume/day, annual or daily traffic peak flow.

Origin and destination studies

Traffic flow patterns

Mass transportation facilities

Accidents, cause and cost analysis

Engineering studies: This

involves Topographic study

Soil details

Location and classification of existing roads

Road life studies

Specific problems in drainage constructions &

maintenance.

Smartworld.asia 25


MASTER PLAN:

Master plan is referred to as road development plan of a city;

district or a street or for whole country. It is an ideal plan showing full

development of the area at some future date. It serves as the guide for the

plan to improve some of the existing roads and to plan the network of new

roads.

It helps in controlling the industrial, commercial and agricultural

and habitat growth in a systematic way of that area. It gives a perceptive

picture of a fully developed area in a plan and scientific way.

Stages in the preparation of master plan:

Data Collection: It includes data regarding existing land use,

industrial and agricultural growth, population, traffic flow,

topography, future trends.

Preparation of draft plan and invite suggestions and comments from

public and experts.

Revision of draft plan in view of the discussions and comments

from experts and public.

Comparison of various alternate proposals of road

system and finding out the sequence in which the

master plan will be implemented

In India targeted road lengths were fixed in various road plans, based on

population, area and agricultural and industrial products. The same way it may be taken

as a guide to decide the total length of road system in each alternate proposal while

preparing a master plan for a town or locality.

Smartworld.asia 26


Preparation of Plans:

Plan-1: This plan should give the topographical details related to existing road

network, drainage, structures, towns and villages with population, agricultural,

industrial and commercial activities.

Plan-2: Should give the details pertaining to the distribution of

population

Plan-3: Should indicate the location of places with productivity.

Plan-4: Should indicate the existing network of roads and proposals

received. Ultimately, the Master plan is the one to be implemented.

SATURATION SYSTEM:

In this system optimum road length is calculated for an area based on the

concept of attaining maximum utility per unit length of the road. This is also

called as maximum utility system.

Factors to attain maximum utility per unit length are:

Population served by the road network

Productivity (industrial and agricultural) served by the road network.

The various steps to be taken to obtain maximum utility per unit length are:

Population factors or units: Since, the area under consideration consists of

villages and towns with different population these are grouped into some

convenient population range and some reasoning values of utility units to each

range of population serve are assigned.

Population less than 500, utility unit = 0.25

501 to 1001, utility unit = 0.50

1001 to 2000, utility unit = 1.00

2001 to 5000, utility unit = 2.00 etc.

Smartworld.asia 27


Productivity Factors or units: The total agricultural and industrial products

served by each road system are worked out and the productivity served may be

assigned appropriate values of utility units per unit weight.

Optimum Road length: Based on the master plan the targeted road length is

fixed for the country on the basis of area or population and production or both.

And the same may be taken as a guide to decide the total length of the road

system in each proposal.

ROAD DEVELOPMENT IN INDIA:

The first attempt for proper planning of the highway development programme in

India on a long term basis was made at the Nagpur Conference in 1943. After, the

completion of the Nagpur Road Plan targets, the Second Twenty year Plan was drawn

for the period 1961-1981. The Third Twenty Year Road Development Plan for the

period 1981-2001 was approved only by the year 1984.

First 20-Year Road Plan (Nagpur Road plan):

This plan was formed in the year 1943 at Nagpur. The plan period was from

1943-1963.Two plan formulae were finalized at the Nagpur Conference for deciding

two categories of road length for the country as a whole as well as for individual areas

(like district). This was the first attempt for highway planning in India. The two plan

formulae assumed the Star and Grid pattern of road network. Hence, the two formulae

are also called “Star and Grid Formulae”.

Salient Features of Nagpur Road Plan:

The roads are classified as,

o Primary System (NH/Expressways)

o Secondary System (SH/MDR)

o Tertiary System(ODR/VR)

Construction and Maintenance of NH was assigned to Central

government It aims for 2, 00,000km of bituminous road and 3,

32,700km of other types.

The formulae were based on star and grid pattern of road network and were

Smartworld.asia 28


considered as two equations:

I –Category: NH/SH/MDR

II-Category: ODR/VR

NH/SH/MDR are meant to provide main grids and ODR/VR as internal road

system the development allowance is 15%

The length of railway track was deducted.

Second Twenty Year Road Plan (Bombay Road Plan):

As the target road length of Nagpur road plan was completed nearly

earlier in 1961 a long term plan was initiated for twenty year period which was

initiated by IRC. Hence, the second twenty year road plan came into picture which

was drawn for the period of 1961-81. The second twenty year road plan was

envisaged overall road length of 10, 57,330 km by the year 1981.

Salient Features of Second 20 year Road Plan:

Aim to provide 32km/100 sq km area

Every town with population above 2000 in plains should be connected by

a bituminous road or metalled road.

>2000 in plains

>1000 in semi-hill area

>500 in hilly area

1600 km length of expressways was proposed

Development allowance is 5% only

Length of railway track was not deducted.

Five equations are given to find NH/SH/MDR/ODR/VR.

Smartworld.asia 29


Comparison of I and II 20-year plans:

First 20-year Plan Second 20-year Plan

Areas is divided into two types

namely, developed and semi-

developed developed areas

Areas is divided into three

types namely, developed; semi-

and undeveloped area.

Two equations are given to

find NH/SH/MDR/ODR/VR

Five equations are given to

find NH/SH/MDR/ODR/VR.

Aim is 16km/100 sq km Aim is 32km/100 sq km.

Development allowance is Development allowance is

15% No express ways 5%. 1600km of expressway

was included.

Length of Railway track was deducted Not deducte

Smartworld.asia 30


Unit 3 Highway alignment

Alignment

The position or the layout of the central line of the highway on the ground is called the

alignment. Horizontal alignment includes straight and curved paths. Vertical alignment

includes level and gradients. Alignment decision is important because a bad alignment

will enhance the construction, maintenance and vehicle operating cost. Once an alignment

is fixed and constructed, it is not easy to change it due to increase in cost of adjoining land

and construction of costly structures by the roadside

Requirements

The requirements of an ideal alignment are

The alignment between two terminal stations should be short and as far as possible

be straight, but due to some practical considerations deviations may be needed.

The alignment should be easy to construct and maintain. It should be easy for the

operation of vehicles. So to the maximum extend easy gradients and curves should

be provided.

It should be safe both from the construction and operating point of view especially

at slopes, embankments, and cutting. It should have safe geometric features.

The alignment should be economical and it can be considered so only when the

initial cost, maintenance cost, and operating cost is minimum.

Factors controlling alignment

We have seen the requirements of an alignment. But it is not always possible to satisfy al

these requirements. Hence we have to make a judicial choice considering all the factors.

The various factors that control the alignment are as follows:

Obligatory points these are the control points governing the highway alignment.

These points are classified into two categories. Points through which it should pass

and points through which it should not pass. Some of the examples are:

Smartworld.asia 31


Bridge site: The Bridge can be located only where the river has straight and

permanent path and also where the abutment and pier can be strongly founded.

The road approach to the bridge should not be curved and skew crossing should be

avoided as possible. Thus to locate a bridge the highway alignment may be

changed.

Mountain: While the alignment passes through a mountain, the various alternatives

are to either

Construct a tunnel or to go round the hills. The suitability of the alternative

depends on factors like topography, site conditions and construction and operation

cost.

Intermediate town: The alignment may be slightly deviated to connect an

intermediate town or village nearby. These were some of the obligatory points

through which the alignment should pass. Coming to the second category that is

the points through which the alignment should not pass are:

Religious places: These have been protected by the law from being acquired for

any purpose. Therefore, these points should be avoided while aligning.

Very costly structures: Acquiring such structures means heavy compensation

which would result in an increase in initial cost. So the alignment may be deviated

not to pass through that point.

Lakes/ponds etc: The presence of a lake or pond on the alignment path would

also Necessitate deviation of the alignment.

Traffic: The alignment should suit the traffic requirements. Based on the origin-

destination data of the area, the desire lines should be drawn. The new alignment

should be drawn keeping in view the desire lines, traffic flow pattern etc.

Geometric design: Geometric design factors such as gradient, radius of curve,

sight distance etc. also governs the alignment of the highway. To keep the radius

of curve minimum, it may be required to change the alignment of the highway.

The alignments should be finalized such that the obstructions to visibility do not

restrict the minimum requirements of sight distance. The design standards vary

with the class of road and the terrain and accordingly the highway should be

aligned.

Smartworld.asia 32


Economy: The alignment finalized should be economical. All the three costs i.e.

construction, maintenance, and operating cost should be minimum. The

construction cost can be decreased much if it is possible to maintain a balance

between cutting and filling. Also try to avoid very high embankments and very

deep cuttings as the construction cost will be very higher in these cases.

Other considerations: various other factors that govern the alignment are

drainage considerations, political factors and monotony.

Smartworld.asia 33


UNIT 4 HIGHWAY GEOMETRIC DESIGN I & II

Introduction

The geometric design of highways deals with the dimensions and layout of visible

features of the highway. The emphasis of the geometric design is to address the

requirement of the driver and the vehicle such as safety, comfort, efficiency, etc. The

features normally considered are the cross section elements, sight distance consideration,

horizontal curvature, gradients, and intersection.

Factors affecting geometric design

Factors affecting the geometric designs are as follows

Design speed:

o Design speed is the single most important factor that affects the geometric design.

It directly affects the sight distance, horizontal curve, and the length of vertical

curves. Since the speed of vehicles vary with driver, terrain etc, a design speed is

adopted for all the geometric design.

Topography:

o It is easier to construct roads with required standards for a plain terrain. However,

for a given design speed, the construction cost increases multi form with the

gradient and the terrain.

Traffic:

It will be uneconomical to design the road for peak traffic flow. Therefore a

reasonable value of traffic volume is selected as the design hourly volume which is

determined from the various traffic data collected.

Environmental:

o Factors like air pollution, noise pollution etc. should be given due consideration in

the geometric design of roads.

Smartworld.asia 34


Economy:

o The design adopted should be economical as far as possible. It should match with

the funds allotted for capital cost and maintenance cost.

Others:

o Geometric design should be such that the aesthetics of the region is not affected

Cross sectional elements

The feature of the cross-section of the pavement influences the life of the pavement as

well as the riding comfort and safety.

Pavement surface characteristics

For a safe and comfortable driving four aspects of the pavement surface are

important;

Friction

Friction between the wheel and the pavement surface is a crucial factor in the

design of horizontal curves and thus the safe operating speed. Further, it also affects the

acceleration and deceleration ability of vehicles. Lack of adequate friction can cause

skidding or slipping of vehicles.

Various factors that affect friction are:

Type of the pavement (like bituminous, concrete, or

gravel), Condition of the pavement (dry or wet, hot or

cold, etc),

Condition of the tire (new or old),

and Speed and load of the vehicle.

The choice of the value of f is a very complicated issue since it depends on many

variables. IRC suggests the coefficient of longitudinal friction as 0.35-0.4 depending on

the speed and coefficient of later friction as 0.15.

Smartworld.asia 35


Unevenness

It affects the vehicle operating cost, speed, riding comfort, safety, fuel

consumption and wear and tear of tires. Unevenness index is a measure of unevenness

which is the cumulative measure of vertical undulation of the pavement surface recorded

per unit horizontal length of the road.

Light reaction

White roads have good visibility at night, but caused glare during day

time. Black roads has no glare during day, but has poor visibility at

night

Drainage

The pavement surface should be absolutely impermeable to prevent seepage of

water into the pavement layers.

Camber

Camber or cant is the cross slope provided to raise middle of the road surface in

the transverse direction to drain off rain water from road surface.

The objectives of providing camber are:

Surface protection especially for gravel and bituminous

roads Sub-grade protection by proper drainage

Quick drying of pavement which in turn increases safety

Too steep slope is undesirable for it will erode the surface. Camber is measured in 1 in

n or n% (Eg. 1 in 50 or2%) and the value depends on the type of pavement surface.

Smartworld.asia 36


Width of carriage way

Width of the carriage way or the width of the pavement depends on the width of the traffic

lane and number of lanes. Width of a traffic lane depends on the width of the vehicle and

the clearance. Side clearance improves operating speed and safety.

Kerbs

Kerbs indicate the boundary between the carriage way and the shoulder or

islands or footpaths. Different types of kerbs are (Figure 12:3):

Low or mountable kerbs:

These types of kerbs are provided such that they encourage the traffic to remain in

the through traffic lanes and also allow the driver to enter the shoulder area with little

difficulty..

Semi-barrier type kerbs:

When the pedestrian traffic is high, these kerbs are provided. Their height is 15 cm

above the pavement edge.

Smartworld.asia 37


Barrier type kerbs:

They are designed to discourage vehicles from leaving the pavement. They

are provided when there is considerable amount of pedestrian traffic. They are

placed at a height of 20 cm above the pavement edge with a steep batter.

Submerged kerbs:

They are used in rural roads. The kerbs are provided at pavement edges between

the pavement edge and shoulders. They provide lateral confinement and stability to the

pavement.

Road margins

The portion of the road beyond the carriageway and on the roadway can be

generally called road margin. Various elements that form the road margins are given

below.

Shoulders

A shoulder are provided along the road edge and is intended for accommodation of

stopped vehicles, serve as an emergency lane for vehicles and provide lateral support for

base and surface courses. The shoulder should be strong enough to bear the weight of a

fully loaded truck even in wet conditions.

Parking lanes

Parking lanes are provided in urban lanes for side parking. Parallel parking is

preferred because it is safe for the vehicles moving in the road. The parking lane should

have a minimum of 3.0 m width in the case of parallel parking .

Bus-bays

Bus bays are provided by recessing the kerbs for bus stops. They are provided so that

they do not obstruct the movement of vehicles in the carriage way.

Smartworld.asia 38


Service roads

Service roads or frontage roads give access to access controlled highways

like freeways and expressways. They run parallel to the highway and will be usually

isolated by a separator and access to the highway will be provided only at selected

points.

Cycle track

Cycle tracks are provided in urban areas when the volume of cycle traffic is

high Minimum width of 2 meter is required, which may be increased by 1 meter for

every additional track.

Footpath

Footpaths are exclusive right of way to pedestrians, especially in urban areas.

They are provided for the safety of the pedestrians when both the pedestrian traffic

and vehicular traffic is high.

Guard rails

They are provided at the edge of the shoulder usually when the road is on an

embankment. They serve to prevent the vehicles from running On the

embankment, especially when the height of the fill exceeds 3 m.

Width of formation

Width of formation or roadway width is the sum of the widths of pavements or

carriage way including separators and shoulders. This does not include the extra

land in formation/cutting. The values suggested by IRC are given in Table

Smartworld.asia 39


Right of way

Right of way (ROW) or land width is the width of land acquired for the road, along its

alignment. It should be adequate to accommodate all the cross-sectional elements of the

highway and may reasonably provide for future development.:

Width of formation: It depends on the category of the highway and width of roadway and

road margins.

Height of embankment or depth of cutting: It is governed by the topography and the

vertical alignment.

Side slopes of embankment or cutting: It depends on the height of the slope, soil type etc.

Drainage system and their size which depends on rainfall, topography etc.

The importance of reserved land is emphasized by the following Extra width of

land is available for the construction of roadside facilities.

Smartworld.asia 40


Figure: A typical Right of way

Sight distance

The safe and efficient operation of vehicles on the road depends very much on the

visibility of the road ahead of the driver.

Types of sight distance

Sight distance available from a point is the actual distance along the road surface, over

which a driver from a specified height above the carriage way has visibility of stationary

or moving objects. Three sight distance situations are considered for design:

Stopping sight distance (SSD) or the absolute minimum sight distance

Intermediate sight distance (ISD) is the defined as twice SSD Overtaking

sight distance (OSD) for safe overtaking operation

Head light sight distance is the distance visible to a driver during night driving under

the illumination of head light

Safe sight distance to enter into an intersection

The most important consideration in all these is that at all times the driver travelling at

the design speed of the highway must have sufficient carriageway distance within his line

of vision to allow him to stop his vehicle before colliding with a slowly moving or

stationary object appearing suddenly in his own traffic lane. The computation of sight

Smartworld.asia 41


distance depends on:

Reaction time of the driver

Reaction time of a driver is the time taken from the instant the object is visible to the

driver to the instant when the brakes are applied. The total reaction time may be split up

into four components based on PIEV theory. In practice, all these times are usually

combined into a total perception- reaction time suitable for design purposes as well as for

easy measurement.

Speed of the vehicle

The speed of the vehicle very much affects the sight distance. Higher the speed, more

time will be required to stop the vehicle. Hence it is evident that, as the speed increases,

sight distance also increases.

Efficiency of brakes

The efficiency of the brakes depends upon the age of the vehicle, vehicle

characteristics etc. If the brake efficiency is 100%, the vehicle will stop the moment the

brakes are applied. But practically, it is not possible to achieve 100% brake efficiency.

Frictional resistance between the tire and the road

The frictional resistance between the tire and road plays an important role to bring the

vehicle to stop. When the frictional resistance is more, the vehicles stop immediately.

Thus sight required will be less. No separate provision for brake efficiency is provided

while computing the sight distance.

Gradient of the road

Gradient of the road also affects the sight distance. While climbing up a gradient, the

vehicle can stop immediately. Therefore sight distance required is less.

Smartworld.asia 42


Stopping sight distance

SSD is the minimum sight distance available on a highway at any spot having

sufficient length to enable the driver to stop a vehicle traveling at design speed, safely

without collision with any other obstruction.

Lag distance is the distance the vehicle traveled during the reaction time t and is given

by vt, where v is the

velocity in m/sec.

Braking distance is the distance traveled by the vehicle during braking operation. For a

levelroad this is obtained by equating the work done in stopping the vehicle and the

kinetic energy of the vehicle. If F is the maximum frictional force developed and the

braking distance is l, then work done against friction in stopping the vehicle is

Fl = fWl where W is the total weight of the vehicle. The

kinetic energy at the design speed is

Therefore, the SSD = lag distance + braking distance and given by:

SSD = vt + v2/

2gf

Where v is the design speed in m/sec, t is the reaction time in sec, g is the acceleration

due to gravity and f is the coefficient of friction. The coefficient of friction f is given

below for

Smartworld.asia 43


Table: Coefficient of longitudinal friction

When there is an ascending gradient of say +n%, the component of gravity adds to

braking action and hence braking distance is decreased. The component of gravity acting

parallel to the surface which adds to the braking force is equal to W sin α = W tanα = Wn=100. Equating kinetic energy and work done:

Similarly the braking distance can be derived for a descending gradient.

Therefore the general equation is given by Equation

Overtaking sight distance

The overtaking sight distance is the minimum distance open to the vision of the

driver of a vehicle intending to overtake the slow vehicle ahead safely against the traffic

in the opposite direction. The overtaking sight distance or passing sight distance is

measured along the center line of the road over which a driver with his eye level 1.2m

above the road surface can see the top of an object 1.2 m above the road surface. The

factors that affect the OSD are: Velocities of the overtaking vehicle, overtaken vehicle

and of the vehicle coming in the opposite direction.

Smartworld.asia 44


Spacing between vehicles, which in-turn depends on the speed

d1 the distance traveled by overtaking vehicle A during the reaction time t = t1 - t0

d2 the distance traveled by the vehicle during the actual overtaking operation T = t3 - t1

d3 is the distance traveled by on-coming vehicle C during the overtaking operation (T).

Therefore:

OSD = d1 + d2 + d3

It is assumed that the vehicle A is forced to reduce its speed to vb, the speed of the slow

moving vehicle Band travels behind it during the reaction time t of the driver. So d1 is

given by:

d1 = vbt

Then the vehicle A starts to accelerate, shifts the lane, overtake and shift back to the

original lane. The vehicle A maintains the spacing s before and after overtaking. The

spacing s in m is given by:

s = 0:7vb + 6

Let T be the duration of actual overtaking. The distance traveled by B during the

overtaking operation is2s+vbT. Also, during this time, vehicle A accelerated from initial

velocity vb and overtaking is completed while reaching final velocity v. Hence the

distance traveled is given by:

The distance traveled by the vehicle C moving at design speed v m=sec during

overtaking operation is given by:

Smartworld.asia 45


The overtaking sight distance is (Figure)

Where vb is the velocity of the slow moving vehicle in m=sec2, t the reaction time of the

driver in sec, s is the spacing between the two vehicle in m given by equation and a is the

overtaking vehicles acceleration in m=sec2. In case the speed of the overtaken vehicle is

not given, it can be assumed that it moves 16 kmph slower the design speed. The

acceleration values of the fast vehicle depends on its speed and given in Table

Table : Maximum overtaking acceleration at different speeds

Overtaking zones

Overtaking zones are provided when OSD cannot be provided throughout the

length of the highway. These are zones dedicated for overtaking operation, marked with

wide roads. The desirable length of overtaking zones is 5 time OSD and the minimum is

three times OSD (Figure 13:2).

Smartworld.asia 46


Sight distance at intersections

At intersections where two or more roads meet, visibility should be

provided for the drivers approaching the intersection from either sides. They

should be able to perceive a hazard and stop the vehicle if required.:

o Enabling approaching vehicle to change the

speed o Enabling approaching vehicle to stop

o Enabling stopped vehicle to cross a main road

Horizontal curve

The presence of horizontal curve imparts centrifugal force which is reactive force

acting outward on a vehicle negotiating it. Centrifugal force depends on speed and

radius of the horizontal curve and is counteracted to a certain extent by transverse

friction between the tyre and pavement surface. On a curved road, this force tends

to cause the vehicle to overrun or to slide outward from the centre of road

curvature. The centrifugal force P in kg=m2 is given by

Smartworld.asia 47


P =Wv2/gR

where W is the weight of the vehicle in kg, v is the speed of the vehicle in m=sec,

g is the acceleration due to gravity in m=sec2 and R is the radius of the curve in

m. The centrifugal ratio or the impact factor P/W is given by P/W=b/2h

The centrifugal force has two effects: a tendency to overturn the vehicle about the

outer wheels and a tendency for transverse skidding. Taking moments of the

forces with respect to

the other when the vehicle is just about to override is give as:

Ph = W b

2

At the equilibrium over turning is possible when

V2 = b gR 2h

And for safety the following condition must satisfy:

b/2h>v2/gR

Smartworld.asia 48


The second tendency of the vehicle is for transverse skidding. i.e. When the centrifugal

force P is greater than the maximum possible transverse skid resistance due to friction

between the pavement surface and tire. The transverse skid resistance (F) is given by:

F=FA+FB

= f(RA + RB)

= fW

where FA and FB is the fractional force at tire A and B, RA and RB is the reaction at

tire A and B, f is the lateral coefficient of friction and W is the weight of the vehicle.

This is counteracted by the centrifugal force (P), and equating:

P = fW or

P = i

At equilibrium, when skidding takes place (from equation14.2)

P = f = v2 W gR

If this equation is violated, the vehicle will overturn at the horizontal curve and if

equation 14.4 is violated, the vehicle will skid at the horizontal curve

Analysis of super-elevation

Super-elevation or cant or banking is the transverse slope provided at horizontal

curve to counteract the centrifugal force, by raising the outer edge of the pavement with

respect to the inner edge, throughout the length of the horizontal curve.

Smartworld.asia 49


Forces acting on a vehicle on horizontal curve of radius R m at a speed of v m/s

are:

P the centrifugal force acting horizontally out-wards through the center of

gravity, W the weight of the vehicle acting down-wards through the center of

gravity, and F the friction force between the wheels and the pavement, along the

surface inward.

At equilibrium, by resolving the forces parallel to the surface of the pavement we get,

At equilibrium, by resolving the forces parallel to the surface of the pavement we get,

P cosθ = W sin θ + FA + FB

= W sin θ + f (RA + RB)

= W sin θ + f (W cos θ + P sin θ)

where W is the weight of the vehicle, P is the centrifugal force, f is the coefficient of

friction, f is the transverse slope due to super elevation. Dividing by W cos θ, we get:

Smartworld.asia 50


Attainment of super-elevation

Elimination of the crown of the cambered section by:

Rotating the outer edge about the crown: The outer half of the cross slope is

rotated about the crown at a desired rate such that this surface falls on the same

plane as the inner half.

Rotation of the pavement cross section to attain full super elevation

There are two methods of attaining super elevation by rotating the pavement

Rotation about the center line : The pavement is rotated such that the inner edge is

depressed and the outer edge is raised both by half the total amount of super

elevation, i.e., by E=2 with respect to the centre

Rotation about the inner edge: Here the pavement is rotated raising the outer edge

as well as the centre such that the outer edge is raised by the full amount of

superelevation with respect to the inner edge.

Smartworld.asia 51


Mechanical widening

The reasons for the mechanical widening are: When a vehicle negotiates a

horizontal curve, the rear wheels follow a path of shorter radius than the front wheels as

shown in figure. this phenomenon is called off tracking, and has the effect of increasing

the effective width of a road space required by the vehicle. Therefore, to provide the same

clearance between vehicles travelling in opposite direction on curved roads as is provided

on straight sections, there must be extra width of carriageway available.. The expression

for extra width can be derived from the simple geometry of a vehicle at a horizontal curve

as shown in figure Let R1 is the radius of the outer track line of the rear wheel, R2 is the

radius of the outer track line of the front wheel l is the distance between the front and rear

wheel, n is the number of lanes, then the mechanical widening Wm (is derive below:

If the road has n lanes, the extra widening should be provided on each lane. Therefore,

the extra widening of a road with n lanes is given

by,

Smartworld.asia 52


Psychological widening

Widening of pavements has to be done for some psychological reasons also. There is a

tendency for the drivers to drive close to the edges of the pavement on curves. Some extra

space is to be provided for more clearance for the crossing and overtaking operations on

curves. IRC proposed an empirical relation for the psychological widening at horizontal

curves Wps

Horizontal Transition Curves

Transition curve is provided to change the horizontal alignment from straight to

circular curve gradually and has a radius which decreases from infinity at the straight end

(tangent point) to the desired radius of the circular curve at the other end (curve point)

There are five objectives for providing transition curve and are given below:

1. To introduce gradually the centrifugal force between the tangent point and the

beginning of the circular curve, avoiding sudden jerk on the vehicle. This increases the

comfort of passengers. To enable the driver turn the steering gradually for his own comfort and security

Type of transition curve

Different types of transition curves are spiral or clothoid, cubic parabola, and

Lemniscates. IRC recommends spiral as the transition curve because:

1. It full fills the requirement of an ideal transition curve, that is;

(a) rate of change or centrifugal acceleration is consistent (smooth) and

Smartworld.asia 53


(b) Radius of the transition curve is 1 at the straight edge and changes to R at the curve

point (Ls / 1R) and calculation and field implementation is very easy.

Length of transition curve

The length of the transition curve should be determined as the maximum of the

following three criteria: rate of change of centrifugal acceleration, rate of change of super

elevation, and an empirical formula given by IRC.

1. Rate of change of centrifugal acceleration

At the tangent point, radius is infinity and hence centrifugal acceleration is zero. At

the end of the transition, the radius R has minimum value R. If c is the rate of change of

centrifugal acceleration, it can be written as:

The length of the transition curve Ls1 in m is

Ls1 = V3

cR

where c is the rate of change of centrifugal acceleration given by an empirical

formula suggested by IRC as

c = ____80____ 75 + 3.6v

Cmin = 0:5; Cmax = 0:8:

2. Rate of introduction of super-elevation

Raise (E) of the outer edge with respect to inner edge is given

by E = eB = e(W +We). The rate of change of this raise from 0 to

E is achieved gradually with a gradient of 1 in N over the length

of the transition curve (typical range of N is 60-150). Therefore,

the length of the transition curve Ls2 is:

Smartworld.asia 54


Ls2 = Ne (W +We)

3. By empirical formula

IRC suggest the length of the transition curve is minimum for a plain and rolling terrain:

Ls3 = 35v2 R

Steep and hilly terrain is: Ls3 =12.96v2

R

And the shift is as:

S=(Ls) 2/24R

The length of the transition curve Ls is the maximum of equations

Ls = Max: (Ls1; Ls2 ;Ls3 )

Setback Distance

Setback distance m or the clearance distance is the distance required from the centerline

of a horizontal curve to an obstruction on the inner side of the curve to provide adequate

sight distance at a horizontal curve. The set back distance depends on:

Smartworld.asia 55


1. Sight distance (OSD, ISD and OSD),

2. Radius of the curve, and

3. Length of the curve.

Case (a) Ls < Lc For single lane roads:

Smartworld.asia 56


Case (b) Ls > Lc

For single lane:

Curve Resistance

When the vehicle negotiates a horizontal curve, the direction of rotation of the front and

the r ear wheels are different. The front wheels are turned to move the vehicle along the

curve, whereas the rear wheels seldom turn. This is illustrated in figure 16:4.The rear

wheels exert a tractive force T in the PQ direction. The tractive force available on the

front wheels is Tcosθ in the PS direction as shown in the figure 16:4. This is less than the actual tractive force, T applied. Hence, the loss of tractive force for a vehicle to negotiate

a horizontal curve is:

CR = T -- T cosα

Smartworld.asia 57


Vertical alignment

The vertical alignment of a road consists of gradients(straight lines in a vertical

plane) and vertical curves. The vertical alignment is usually drawn as a profile, which is a

graph with elevation as vertical axis and the horizontal distance along the centre line of

the road as the the horizontal axis.

Gradient

Gradient is the rate of rise or fall along the length of the road with respect to the

horizontal. While aligning a highway, the gradient is decided designing the vertical curve.

Before finalising the gradients, the construction cost, vehicular operation cost and the

practical problems in the site also has to be considered.

Types of gradient

Many studies have shown that gradient upto seven percent can have considerable

effect on the speeds of the passenger cars. On the contrary, the speeds of the heavy

vehicles are considerably reduced when long gradients a sat as two percent is adopted.

Although, atter gradients are desirable, it is evident that the cost of construction will also

be very high.

Ruling gradient

The ruling gradient or the design gradient is the maximum gradient with which the

designer attempts to design the vertical profile of the road. This depends on the terrain,

length of the grade, speed, pulling power of the vehicle and the presence of the horizontal

curve. In atter terrain, it may be possible to provide at gradients, but in hilly terrain it is

not economical and sometimes not possible also.

Smartworld.asia 58


Minimum gradient

This is important only at locations where surface drainage is important. Camber

will take care of the lateral drainage. But the longitudinal drainage along the side drains

requires some slope for smooth flow of water.

Limiting gradient

This gradient is adopted when the ruling gradient results in enormous increase in

cost of construction. On rolling terrain and hilly terrain it may be frequently necessary to

adopt limiting gradient.

Exceptional gradient

Exceptional gradient are very steeper gradients given at unavoidable situations.

They should be limited for short stretches not exceeding about 100 meters at a stretch.

Summit curve

Summit curves are vertical curves with gradient upwards. They are formed when

two gradients meet as illustrated in figure below in any of the following four ways:

1. When a positive gradient meets another positive gradient

2. When positive gradient meets a at gradient

3. When an ascending gradient meets a descending gradient.

4. When a descending gradient meets another descending gradient

Smartworld.asia 59


Type of Summit Curve

Many curve forms can be used with satisfactory results; the common practice

has been to use parabolic curves in summit curves. This is primarily because of the

ease with it can be laid out as well as allowing a comfortable transition from one

gradient to another.

Length of the summit curve

The important design aspect of the summit curve is the determination of the length

of the curve which is parabolic. As noted earlier, the length of the curve is guided by the

sight distance consideration.

Distance .Let L is the length

Case a: Length of summit curve greater than sight distance

The situation when the sight distance is less than the length of the curve

Smartworld.asia 60


Case b: Length of summit curve less than sight distance

When stopping sight distance is considered the height of driver's eye above the road

surface (h1) is taken as 1.2 meters, and height of object above the pavement surface (h2)

is taken as 0.15 meters. If overtaking sight distance is considered, then the value of

driver's eye height (h1) and the height of the obstruction (h2) are taken equal as 1.2

meters.

Smartworld.asia 61


Valley curve

Valley curve or sag curves are vertical curves with convexity downwards. They

are formed when two gradients meet as illustrated in figure below in any of the

following four ways:

1. When a descending gradient meets another descending gradient

2. When a descending gradient meets a at gradient 3. When a descending gradient meets an ascending gradient 4. When an ascending gradient meets another ascending gradient

Length of the valley curve

The valley curve is made fully transitional by providing two similar transition curves of

equal length The transitional curve is set out by a cubic parabola y = bx3 where b =

2N3/

L2 The length of the valley transition curve is designed based on two criteria:

1. Comfort criteria; that is allowable rate of change of centrifugal acceleration is limited

Smartworld.asia 62


to a comfortable level of about 0:6m=sec3.

2. Safety criteria; that is the driver should have adequate headlight sight distance at any

part of the country.

Comfort criteria

The length of the valley curve based on the rate of change of centrifugal

acceleration that will ensure comfort: Let c is the rate of change of acceleration, R the

minimum radius of

the curve, v is the design speed and t is the time, then c is given as:

Ls = v3/CR

For a cubic parabola, the value of R for length Ls is given by:

R = Ls N

Safety criteria

Length of the valley curve for headlight distance may be determined for two conditions:

length of the valley curve greater than stopping sight distance

and Length of the valley curve less than the stopping sight

distance.

Case 1: Length of valley curve greater than stopping sight distance (L > S)

The total length of valley curve L is greater than the stopping sight distance SSD.

The sight distance available will be minimum when the vehicle is in the lowest point in

the valley. This is because the beginning of the curve will have infinite radius and the

bottom of the curve will have minimum radius which is a property of the transition curve.

Smartworld.asia 63


Where L is the total length of valley curve, N is the deviation angle in radians or tangent

of the deviation angle or the algebraic difference in grades, and c is the allowable rate of

change of centrifugal acceleration which may be taken as 0:6m/sec3.

Where N is the deviation angle in radians, h1 is the height of headlight beam, α is the head beam inclination in degrees and S is the sight distance. The inclination α is = 1 degree.

Case 2 Length of valley curve less than stopping sight distance (L < S)

The length of the curve L is less than SSD. In this case the minimum sight distance

is from the beginning of the curve. The important points are the beginning of the curve

and the bottom most part of the curve. If the vehicle is at the bottom of the curve, then its

headlight beam will reach far beyond the endpoint of the curve whereas, if the vehicle is

at the beginning of the curve, then the headlight beam will hit just outside the curve.

Therefore, the length of the curve is derived by assuming the vehicle at the beginning of

the curve. The case is shown in figure below.

Smartworld.asia 64


The gradients are very small and are acceptable for all practical purposes. We will not

be able to know prior to which case to be adopted. Therefore both has to be calculated

and the one which satisfies the condition is adopted.

Smartworld.asia 65


UNIT 5 PAVEMENT MATERIALS

Introduction

Subgrade soil

Subgrade soil is an integral part of the road pavement structure which directly

receives the traffic load from the pavement layers. The subgrade soil and its properties are

important in the design of pavement structure. The main function of the subgrade is to

give adequate support to the pavement and for this the subgrade should possess sufficient

stability under adverse climate and loading conditions.

The formation of waves, corrugations, rutting and shoving in black top pavements

and the phenomena of pumping, blowing and consequent cracking of cement concrete

pavements

are generally attributed due to the poor subgrade conditions.

Desirable Properties

The desirable properties of soil as a highway material are

Stability

Incompressibility

Permanency of strength

Minimum changes in volume and stability under adverse conditions of weather and

ground water

Good drainage, and

Ease of compaction.

The soil should possess adequate stability or resistance to permanent deformation

under loads, and should possess resistance to weathering, thus retaining the desired

subgrade support. Minimum variation in volume will ensure minimum variation in

differential

Smartworld.asia 66


Soil classification

1. Grain size analysis

According to size of grains soil is classified as gravel, sand, silt and clay. As per

Indian standard classification the limits of grain size are as follows.

Gravel Sand Silt Clay

C M F C M F C M F

0.6 0.2

0.02 0.006 0.006 0.002

2.0mm 0.06mm 0.002mm

Fraction of soils

Larger than 2.00mm size Gravel

Between 2.00mm – 0.06 mm size Sand

Between 0.06mm – 0.002 mm size Silt

Smaller than 0.002 size Clay

2. Highway Research Board (HRB) classification of soils

This is also called American Association of State Highway Officials (AASHO)

classification of Revised Public Roads Administration (PRA) soil classification system.

Soils are divided into seven groups A-I to A-7. A-I, A-2 and A-3 soils are granular soils,

percentage fines passing 0.074 mm sieve being less than 35. A-4, A-5, A-6 and A-7, soils

are fine grained or silt-clay soils, passing 0.074 mm sieve being greater than 35 percent.

A-1 soils are well graded mixture of stone fragments, gravel coarse sand, fine sand

and non-plastic or slightly plastic soil binder. The soils of this group are subdivided into

two subgroups, A- 1-a, consisting predominantly of stone fragments or gravel and A-I-b

consisting predominantly of coarse sand.

A-2 group of soils include a wide range of granular soils ranging from A- 1 to A-3

groups, consisting of granular soils and upto 35% fines of A-4, A-5, A-6 or A-7 groups.

Based on the fines content, the soils of A-2 groups are subdivided into subgroups A-2-4,

Smartworld.asia 67


A-2-5, A-2-6 and A-2-7.

A-3 soils consist mainly, uniformly graded medium or fine sand similar to beach

sand or desert blown sand. Stream-deposited mixtures of poorly graded fine sand with

some coarse sand and gravel are also included in this group.

A-4 soils are generally silty soils, non-plastic or moderately plastic in nature with

liquid limit and plasticity index values less than 40 and 10 respectively

A-5 soils are also silty soils with plasticity index less than 10%, but with liquid

limit values exceeding 40%. These include highly elastic or compressible, soils, usually

of diatomaceous of micaceous character.

A-6 group of soils are plastic clays, having high values of plasticity index

exceeding 10% and low values of liquid limit below 40%; they have high volume change

properties with variation in moisture content.

A-7 soils are also clayey soils as A-6 soils, but with high values of both liquid limit and

plasticity index

California Bearing Ratio (CBR) Test

This is a penetration test developed by the California division of

highway. For evaluating the stability of soil subgrade and other pavement

materials. The test results have been correlated with flexible pavement thickness

requirement for highway and airfield. CBR test may be conducted in the laboratory

on a prepared specimen in a mould or in situ in the field.

Laboratory CBR test

The laboratory CBR apparatus consists of

Cylindrical mould

Mould 150mm dia, 175mm height with 50mm collar height, detachable perforated

base with spacer disc of 148mm dia and 47.7mm thick is used to obtain a

specimen of exactly 127.3mm height.

Loading Machine

Smartworld.asia 68


Compression machine operated at a constant rate of 1.25mm/min.Loading frame

with cylindrical plunger 50mm dia & dial gauge for measuring the deformation

due to application of load.

Compaction rammer

Type of compaction No of layers Wt of hammer Fall (cm) No of blows

(kg)

Light compaction 3 2.6 31 56

Heavy compaction 5 4.89 45 56

Annular weight or surcharge weight

2.5 Kgs of surcharge wt of 147mm dia are placed on specimen both at the soaking

and testing of prepared samples.

Procedure:

CBR test may be performed on undisturbed soil specimens.

About 5kgs of soil is taken passing though 20mm IS sieve and retained on 4.75mm IS

sieve

The soil is mixed with water upto OMC.

The spacer disc is placed at the bottom of the mould over the base plate & a coarse

filter paper is placed over the spacer disc.

Then the moist soil sample is to be compacted over this in the mould by adopting

either IS light compaction or IS heavy compaction.

For IS heavy compaction 3 equal layers of compacted thickness about 44mm by

applying 56 evenly distributed blows from 2.6kgs rammer.

For IS heavy compaction 5 equal layers of compacted thickness about 26.5mm by

applying 56 evenly distributed blows from 4.89 kg rammer.

After compacting the last layer, The collar is removed and the excess soil above the

top of the mould is evenly trimmed off by means of straight edge (of 5mm thickness).

Clamps are removed ant the mould with compacted soil is lifted leaving below the

perforated base plate & the spacer disc which is removed.

Smartworld.asia 69


Then the mould with compacted soil is weighed

Filter paper is placed on the perforated base plate & the mould with compacted soil is

inverted & placed in position over the base plate.

Now the clamps of the base is tightened

Another filter paper is placed on the placed on the top surface of the sample & the

perforated plate with adjustable stem is placed over it.

Now surcharge weights of 2.5 or 5kgs are placed over the perforated plate & the

whole mould with the weights is placed in a water tank for soaking such that water

can enter the specimen both from the top & bottom.

The initial dial gauge readings is recorded & the test set up is kept undisturbed in the

water tank to allow soaking of the soil specimen for full 4 days or 96 hrs.

The final dial gauge reading is noted to measure the expansion & swelling of the

specimen due to soaking.

The swell measurement assembly is removed, the mould is taken out of the water tank

& the sample is allowed to drain in a perpendicular position for 15 min surcharge wt,

perforated plate with stem, filter paper are removed.

The mould with the soil subgrade is removed from the base plate & is weighed again

to determine the wt of water absorbed.

Then the specimen is clamped over base plate surcharge wt‟s are placed on specimens centrally such that the penetration test could be conducted.

The mould with base plate is placed under the penetration plunger of loading machine.

The penetration plunger is seated +at the centre of the specimen & is brought in

contact with the top surface of the soil sample by applying a seating load of 4kgs.

The dial gauge for measuring the penetration values of the plunger is fitted in

position The dial gauge of proving ring & the penetration dial gauge are set to 0.

The load is applied though the penetration plunger at a uniform rate of 1.5mm/min

The load reading are recorded at penetration reading 0, 0.5, 1.0, 1.5, 2, 2.5, 3, 4, 5,

7.5, 10 & 12.5mm.

Smartworld.asia 70


In case the load reading starts decreasing before 12.5mm penetration, the max load &

the corresponding penetration values are recorded.

After the final reading the load is released & the mould from loading machine.

The proving ring calibration factor is noted so that load dial gauge value can be

converted into the load in kg.

Calculation :

Swelling or expansion ratio is calculated from the

formula. Expansion ratio = (100 ( df – di))/h

Where,

df = Final dial gauge after soaking in mm

di = Initial dial gauge before soaking in

mm h = initial ht of the specimen in mm

Therefore, CBR= Load sustained by the specimen at 2.5 or 5mm penetration x

100

Load sustained by std specimen at corresponding penetration level

CBR at 2.5mm = P1(kg) x 100%

1370

CBR at 5mm = P2(kg) x 100%

2055

Generally CBR value @ 2.5mm penetration is higher & this value is adopted.

The initial upward concavity of the load penetration is due to the piston surface not

being fully in contact with top of the specimen.

Top layer of soaked soil being too soft.

Smartworld.asia 71


Modulus of subgrade reaction of soil

Plate bearing test

The plate bearing test has been devised to evaluate the supporting power of

subgrade or any other pavement layer by using plates of larger diameter.

Plate bearing test was originally meant to find the modulus of subgrade reaction in

the westergards‟s analysis for wheel load stresses in cement concrete pavement.

In the plate bearing test a compressive stress is applied to the soil or pavement layer

through rigid plates of relatively large size & the deflection are measurement for

various stress values.

The deflection level is generally limited to a low value of 1.25mm to 5mm.

Modulus subgrade reaction (k)

K may be defined as the pressure sustained per unit deformation of subgrade

at specified pressure level using specified plate size.

The standard palte size for finding K value is 75cm dia in same test a smaller

plate of 30cm dia is also used (75,60,45,30 & 22.5 cm dia).

Apparatus used

Bearing plate:

Mild steel of 75cm dia & 1.5 to 2.5 cm thickness.

Loading equipment:

Reaction frame or dead load applied may be measured either by a proving ring or dial

gauge assembly.

Settlement measurement:

It may be made by means of 3 or 4 dial gauge fixed on the periphery of the bearing plate

from an independent datum frame. Datum frame should be supported from the loaded

Smartworld.asia 72


area.

Procedure

At the test site, about 20cm top soil is removed & the site is leveled & the plate is

properly seated on the prepared surface.

The stiffening plates of decreasing dia are placed & the jack & proving ring assembly

are fitted to provide reaction against the frame.

3 or 4 dial gauges are fixed on the periphery of the palte from the independent datum

frame for measuring settlement.

A seating load of 0.07 kg/cm2 (320kgs for 75 dia) is applied & released after a few

sec. The settlement dial gauges reading are now noted corresponding to zero load.

A load is applied by means of jack sufficient to cause an average settlement of about

0.25mm.

When there is no perception increase in settlement or when the rate of settlement is

less than 0.025mm/min (case of clayey soil or wet soil), the reading of the settlement

dial gauge are noted & the avg settlement is found & the load is noted from the

proving ring dial reading.

The load is then increased till settlement increases to a further amount of about

0.25mm

& the avg settlement & load are found.

The procedure is repeated till the settlement reaches 0.175cm.

A graph is plotted with mean settlement versus mean bearing pressure (load/unitarea)

as shown in fig.

Bearing pressure settlement curve.

The pressure p (kg/cm2) corresponding to a settlement delta = 0.125cm (obtaines

from the graph shown above)

The modulus of subgrade reaction k is calculated from the relation.

K = P kg/cm2

0.125

Smartworld.asia 73


Correction for smaller plate size

In some cases the load capacity may not be adequate to cause 75cm dia plate to settle

0.175cm.

In such a case a plate of smaller dia (say 30cm) may be used.

Then K value should be found by applying a suitable correction for plate size.

Assuming the subgrade to be an elastic medium with modulus of elasticity E

(kg/cm2), the theoretical relationship of deformation (cm) under a rigid plate of radius

a (cm) is given by

Delta = 1.18Pa

E

But, K = P

D

Substitute the value of D in K

Therefore K = P x E

1.18 Pa K = E

1.18a

If the value of E is taken as constant for a soil, Then k x a = constant

i.e. Ka = ka or K = ka

A

Hence if the test is carried out with a smaller plate of radius a & the modulus of subgrade

reaction K is found.

Then the corrected value of modulus of subgrade reaction K for std plate of radius a, is

given by K = k1 a1

A

AGGREGATES

Introduction

Aggregates form the major portion of pavement structure and they form the prime

materials used in pavement construction. Aggregates have to bear stresses occurring due

Smartworld.asia 74


to the wheel loads on the pavement and on the surface course they also have to resist wear

due to abrasive action of traffic.

Strength

The aggregates to be used in road construction should be sufficiently strong to

withstand the stresses due to traffic wheel load. The aggregates which are to be used in

top layers of the pavements, particularly in the wearing course have to be capable of

with4jnhighs1cssesinaddItion to - wear and tear; hence they should possess sufficient

strength resistance to crushing.

Toughness

Aggregates in the pavements are also subjected to impact due to moving wheel

loads. Sever impact like hammering is quite move on water bound macadam roads where

stones protrude out especially after the monsoons.

Durability

The stone used in pavement construction should be durable and should resist

disintegration due to the action of weather. The property of the stones to withstand the

adverse action of weather may called soundness.

Shape of Aggregates

The size of the aggregates is first qualified by the size of square sieve opening

through which an aggregate may pass, and not by the shape. Aggregates which happen to

fall in a particular size range may have rounded, cubical, angular flaky or elongated shape

of particles. It is e and donated particles will have less strength and durability when

compared with cubical angular or rounded articles of the same Stone. Hence too flaky and

too much elongated aggregates should be avoided as far as possible.

Adhesion with Bitumen

The aggregates used in bituminous pavements should have less affinity with water

when compared with bituminous materials, otherwise the bituminous coating on the

aggregate will be stripped off in presence of water.

Tests for Road Aggregate

Smartworld.asia 75


In order to decide the suitability of the road stones for use in construction, the

following tests are carried out:

(a) Crushing test

(b) Abrasion test

(c) Impact test

(d) Soundness

(e) Shape test

(f) Specific gravity and water absorption test (g) Bitumen adhesion test

The essential features of these tests are discussed below. Separate tests are

available for testing cylindrical stone specimens and coarse aggregates for crushing,

abrasion and impact tests. But due to the difficulties of preparing cylindrical stone

specimen which need costly core drilling, cutting and polishing equipment, the use of

such tests are now limited. Testing of aggregates is easy and simulate the field condition

better, as such these are generally preferred.

BITUMINOUS MATERIALS

Introduction

Bituminous binders used in pavement construction works include both bitumen

and tar. Bitumen is a petroleum product obtained by the distillation of petroleum crude

where-as road tar is obtained by the destructive distillation of coal or wood. Both bitumen

and tar have similar appearance, black in colour though they have different

characteristics. Both these materials can be used for pavement works.

(i) paving bitumen from Assam petroleum, denoted as A-type and designated as

grades A35, A 90, etc.

(ii) paving bitumen from other sources denoted as S-type and designated as grades S

35, S 90, etc.

Types of Bituminous Materials

Smartworld.asia 76


Bituminous material used in highway construction may be broadly divided as

(i) Bitumen and

(ii) Tar

Bitumen may be further divided as petroleum asphalt or bitumen and native asphalt. There

are different forms in which native asphalts are available. Native asphalts are those which

occur in a pure or nearly pure state in nature. Native asphalts which are associated with a

large proportion of mineral matter are called rock asphalts.

Bitumen

Crude petroleum obtained from different places are quite different in their

composition. The portion of bituminous material present in the petroleum‟s may widely differ depending on the source. Almost all the crude petroleum‟s contain considerable amounts of water along with crude oil. Hence the petroleum should be dehydrated first

before carrying out the distillation. General types of distillation processes are fractional

distillation and

Tests on Bitumen

Bitumen is available in a variety of types and grades. To judge the suitability of

these binders various physical tests have been specified by agencies like ASTM, Asphalt

Institute, British Standards Institution and the ISI. These tests include penetration test,

ductility tests, softening point test and viscosity test. For classifying bitumen and studying

the performance of bituminous pavements, the penetration and ductility tests are essential.

The various tests on bituminous materials are

(a) Penetration tests (b) Ductility tests (c) Viscosity tests

(d) Float test (e) Specific gravity test (f) Softening point test

(g) Flash and Fire point test (h) Solubility test (i) Spot test

(j) Loss on heating test (k) Water content test

Cutback Bitumen

Cutback bitumen is defined as the bitumen, the viscosity of which has been reduced by a

Smartworld.asia 77


volatile dilutant. For use in surface dressings, some type of bitumen macadam and soil

bitumen it is necessary to have a fluid binder which can be mixed relatively at low

temperatures. Hence to increase fluidity of the bituminous binder at low temperatures the

binder is blended with a volatile solvent. After the cutback mix in construction work, the

volatile gets evaporated and the cutback develops the properties. The viscosity of the

cutback and rate of which it hardens on the road depend on the characteristics and

quantity of both bitumen and volatile oil used as the diluent. Cutback bitumens are

available in three types, namely,

(i) Rapid Curing (RC)

(ii) Medium Curing (MC) and

(iii) Slow Curing (SC)

This classification is based on the rate of curing or hardening after the application. The

grade of cutback or its fluidity is designed by a figure which follows the initials; as an

example RC-2 means that it is a rapid curing cutback of grade 2.The cutback with the

lowest viscosity is designated by numeral 0, such as RC-0 and SC-0. Suffix numerals 0, 1,

2, 3, 4 and 5 designate progressively thicker or more viscous cutbacks as the numbers

increase. This number indicates a definite viscosity irrespective of the type of cutback; in

other words, RC-2, MC-2 all have the same initial viscosity at a specified temperature.

The initial viscosity values (in seconds, standard tar viscometer) of various grades of

cutbacks as per ISI specifications are given in Table 6.7.

Thus lower grade cutbacks like RC-0, RC-l etc. would contain high prop solvent

when compared with higher grades like RC-4 or RC-5, RC-0 and MC-0 may contain

approximately 45 percent solvent and 55 percent bitumen, whereas, RC-5 and MC-5 may

contain approximately 15 percent solvent and 85 percent bitumen.

Rapid Curing Cutbacks are bitumens, fluxed or cutback with a petroleum Distillate such

as naphta or gasoline which will rapidly evaporate after using in construction, leaving the

bitumen binder. The grade of the R.C. cutback is governed by the proportion of the

solvent used. The penetration value of residue from distillation up to 3600C of RC

cutback bitumen is 80 to 120.

Medium curing cutbacks are bitumen fluxed to greater fluidity by blending with a

intermediate-boiling-point solvent like kerosene or light diesel oil. MC cutbacks evaporate

relatively at slow rate because the kerosene-range solvents will not evaporate

Smartworld.asia 78


rapidly as the

gasoline-range solvents used in the manufacture of RC cutbacks. Hence the designation

„medium curing‟ is given to this cutback type. MC products have good wetting properties

and so satisfactory coating of fine grain aggregate and sandy soils is possible.

Slow curing cutbacks are obtained either by blending bitumen with high-boiling-

point gas oil, or by controlling the rate of flow and temperature of the crude during the

first cycle of refining. SC cutbacks or wood soils harden or set way slowly as it is a semi

volatile material.

Various tests carried out on cut-backs bitumen are

(a) Viscosity tests at specified temperature using specified size of orifice.

(b) Distillation test to find distillation fractions, up to specified temperature and to

find the residue from distillation up to 360°C

(c) Penetration test, ductility test and test for matter soluble in carbon disulphide on

residue from distillation up to 360°C

(d) Flash point test on cutback using Pensky Martens closed type apparatus.

Bituminous Emulsion

A bitumen emulsion is liquid product in which a substantial amount of bitumen is

suspended in a finely divided condition in an aqueous medium and stabilized by means

of one or more suitable materials. An emulsion is a two phase system consisting of two

immiscible liquids; the one being dispersed as fine globules in the other.Usually, bitumen

or refined tar is broken up into fine globules and kept in suspension in water. A small

proportion of an emulsifier is used to facilitate the formation of dispersion and to keep

the globules of dispersed binder in suspension.

Some of the general properties of road emulsions are judged by the following tests

(i) Residue on Sieving: It is desirable to see that not more than 0.25 percent by w of

emulsion consists of particles greater than 0.15 mm diameter.

(ii) Stability to Mixing with Coarse Graded Aggregate: This test carried out to fit the

emulsion breaks down and coats the aggregate with bitumen too early before

mixing is complete.

Smartworld.asia 79


(iii) Stability to Mixing with Cement : This test is carried out to assess the stability

emulsions when the aggregate contains large proportions of fines.

(iv) Water Cement: To know the percentage water in the emulsion which depend the

type of the emulsion.

(v) Sedimentation: Some sedimentation may occur when a drum of emulsion is

standing before use, but on agitation, the emulsion redisperses and can be used.

(vi) Viscosity: The viscosity of emulsified bitumen should be low enough to be

sprayed through jets or to coat the aggregates in simple mixing.

Three types of bituminous emulsion are prepared, viz., (i) Rapid Setting (RS),

Medium Setting (MS) and (iii) Slow Setting (SS) types. Rapid Setting type emulsion is

suitable for surface dressing and penetration macadam type of construction. Medium

Setting type is used for premixing with coarse aggregates and Slow Setting type emulsion

is suitable for fine aggregate mixes.

Tar:

Tar is the viscous liquid obtained when natural organic materials such as wood and

coal carbonized or destructively distilled in the absence of air. Based on the material from

which tar is derived, it is referred to as wood tar or coal tar; the latter is more widely used

for road work because it is superior. Three stages for the production of road tar are

(i) Carbonization of coal to produce crude tar

(ii) Refining or distillation of crude tar and

(iii) Blending of distillation residue with distillate oil fraction to give the desired road

tar.

There are five grades of roads tars, viz., RT- I, RT-2, RT-3, RT-4 and RT-5,

based on their viscosity and other properties. RT-l has the lowest viscosity and is used

for surface painting under exceptionally cold weather as this has very low viscosity. RT-

2 is recommended for standard surface painting under normal Indian climatic

conditions. RT-3 may be used for surface painting, renewal coats and premixing chips

for top course and light carpets. RT-4 is generally used for premixing tar macadam in

base course. For grouting purposes RT-5 may be adopted, which has the highest

viscosity among the road tars.

Smartworld.asia 80


The various tests that are carried out on road tars are listed below

(i) Specific gravity test

(ii) Viscosity test on standard tar viscometer

(iii) Equiviscous temperature (EVT)

(iv) Softening point

(v) Softening point of residue

(vi) Float test

(vii) Water content

(viii) Distillation fraction on distillation upto 200°C, 200°C to 270°C and 270°C

to 3 30°C.

(ix) Phenols, percent by volume

(x) Naphthalefle, percent by weight

(xi) Matter insoluble in toluene, percent by weight

The requirements for the five grades of road tars based on the above test results are given

by the ISI. Bitumen and tar have black to dark brown colour. But bitumen is a petroleum

product whereas tar is produced by the destructive distillation of coal or wood.

Smartworld.asia 81


Comparison between tar & bitumen

Bitumen Tar

It has black to dark brown color It also has black to dark brown in color

Tar is produced by the destructive

It is natural petroleum product distillation

of coal or wool

It is soluble in carbon disulphide & in carbon Tar is soluble only in toluene

tetrachloride

It has better weather resisting property It has inferior weather resisting property

Bitumen are less temp susceptible Tar is more temp susceptible

Free carbon content is less Free carbon content is More

It neither binds the aggregate well nor retains It binds aggregate more easily & retain it

the presence of water better in the presence of water.

BITUMINOUS PAVING MIXES

Requirements of Bituminous Mixes

The mix design should aim at an economical blend, with proper gradation of

aggregates and adequate proportion of bitumen so as to fulfil the desired properties of

the mix. Bituminous concrete or asphaltic concrete is one of the highest and costliest

types of flexible pavement layers used in the surfacing course. The desirable properties

of a good bituminous mix are stability, durability, flexibility, skid resistance and

workability.

Mix design methods should aim at determining the properties of aggregates and

bituminous material which would give a mix having the following properties.

(i) Sufficient stability to satisfy the service requirements of the pavement and the

traffic conditions, without undue displacement

Smartworld.asia 82


Unit 6 Introduction to pavement design

A highway pavement is a structure consisting of superimposed layers of processed

materials above the natural soil sub-grade, whose primary function is to distribute the

applied vehicle loads to the sub-grade. The pavement structure should be able to provide

a surface of acceptable riding quality, adequate skid resistance, favorable light reflecting

characteristics, and low noise pollution.

Requirements of a pavement

The pavement should meet the following requirements:

Sufficient thickness to distribute the wheel load stresses to a safe value on the

sub-grade soil

Structurally strong to withstand all types of stresses imposed

upon it Adequate coefficient of friction to prevent skidding of

vehicles

Smooth surface to provide comfort to road users even at high speed

Types of pavements

The pavements can be classified based on the structural performance into two,

flexible pavements and rigid pavements. In flexible pavements, wheel loads are

transferred by grain-to-grain contact of the aggregate through the granular structure. The

flexible pavement, having less flexural strength, acts like a flexible sheet (e.g. bituminous

road). On the contrary, in rigid pavements, wheel loads are transferred to sub-grade soil

by flexural strength of the pavement and the pavement acts like a rigid plate (e.g. cement

concrete roads).

Flexible pavements

Flexible pavements will transmit wheel load stresses to the lower layers by grain-to-grain

transfer through the points of contact in the granular structure (see Figure 19:1). The

wheel load acting on the pavement will be distributed to a wider area, and the stress

decreases with the depth. Taking advantage of this stress distribution characteristic

The lower layers will experience lesser magnitude of stress and less quality material can

be used. Flexible pavements are constructed using bituminous materials. These can be

Smartworld.asia 83


either in the form of surface treatments (such as bituminous surface treatments generally

found on low volume roads) or, asphalt concrete surface courses (generally used on high

volume roads such as national highways) pavement layer

Types of Flexible Pavements

The following types of construction have been used in flexible pavement:

Conventional layered flexible

pavement, Full - depth asphalt

pavement, and

Contained rock asphalt mat (CRAM).

Conventional flexible pavements are layered systems with high quality expensive

materials are placed in the top where stresses are high, and low quality cheap materials

are placed in lower layers.

Full - depth asphalt pavements are constructed by placing bituminous layers directly on

the soil subgrade. This is more suitable when there is high traffic and local materials are

not available.

Contained rock asphalt mats are constructed by placing dense/open graded aggregate

layers in between two asphalt layers. Modified dense graded asphalt concrete is placed

above the sub-grade will significantly reduce the vertical compressive strain on soil sub-

grade and protect from surface water

Rigid pavements

Rigid pavements have sufficient flexural strength to transmit the wheel load stresses to a

wider area below. A typical cross section of the rigid pavement is shown in Figure below

Smartworld.asia 84


Compared to flexible pavement, rigid pavements are placed either directly on the prepared

sub-grade or on a single layer of granular or stabilized material.

Since there is only one layer of material between the concrete and the sub-grade, this layer

can be called as base or sub-base course. In rigid pavement, load is distributed by the slab

action, and the pavement behaves like an elastic plate resting on a viscous medium Rigid

pavements are constructed by Portland cement concrete (PCC) and should be analyzed by

plate theory instead of layer theory.

Types of Rigid Pavements

Rigid pavements can be classified into four types:

Jointed plain concrete pavement (JPCP),

Jointed rei forced concrete pavement (JRCP),

Continuous reinforced concrete pavement (CRCP),

and Pre-stressed concrete pavement (PCP).

Jointed Plain Concrete Pavement is plain cement concrete pavements constructed

withclosely spaced contraction joints. Dowel bars or aggregate interlocks are normally

used for load transfer across joints. They normally has a joint spacing of 5 to 10m.

Jointed Reinforced Concrete Pavement Although reinforcements do not improve

thestructural capacity significantly, they can drastically increase the joint spacing to 10 to

Smartworld.asia 85


30m. Dowel bars are required for load transfer. Reinforcements help to keep the slab

together even after cracks.Continuous Reinforced Concrete Pavement Complete

elimination of joints are achieved by reinforcement.

Factors affecting pavement design

Traffic and loading

Traffic is the most important factor in the pavement design. The key factors

include contact pressure, wheel load, axle configuration, moving loads, load, and load

repetitions.

Contact pressure

The tire pressure is an important factor, as it determines the contact area and the

contact pressure between the wheel and the pavement surface. Even though the shape of

the contact area is elliptical, for sake of simplicity in analysis, a circular area is often

considered.

Wheel load

The next important factor is the wheel load which determines the depth of the

pavement required to ensure that the subgrade soil is not failed. Wheel configuration

affects the stress distribution and deflection within a pavement. Many commercial

vehicles have dual rear wheels which ensure that the contact pressure is within the limits.

The normal practice is to convert dual wheel into an equivalent single wheel load so that

the analysis is made simpler.

Axle configuration

The load carrying capacity of the commercial vehicle is further enhanced by the

introduction of multiple axles.

Moving loads

The damage to the pavement is much higher if the vehicle is moving at creep

speed. Many studies show that when the speed is increased from 2 km/hr to 24 km/hr, the

Smartworld.asia 86


stresses and deflection reduced by 40 per cent.

Repetition of Loads

The influence of traffic on pavement not only depends on the magnitude of the

wheel load, but also on the frequency of the load applications. Each load application

causes some deformation and the total deformation is the summation of all these

Environmental factors

Environmental factors affect the performance of the pavement materials and cause

various damages. Environmental factors that affect pavement are of two types,

temperature and precipitation.

Equivalent single wheel load

To carry maximum load within the specified limit and to carry greater load, dual

wheel, or dual tandem assembly is often used. Equivalent single wheel load (ESWL) is

the single wheel load having the same contact pressure, which produces same value of

maximum stress, deflection, tensile stress or contact pressure at the desired depth. The

procedure of finding the ESWL for equal stress criteria is provided below. This is a semi-

rational method, known as Boyd and Foster method, based on the following assumptions:

equalancy concept is based on equal stress; contact area is circular; influence angle is

450; and soil medium is elastic, homogeneous, and isotropic half space.

Where P is the wheel load, S is the center to center distance between the two wheels, d is

the clear distance between two wheels, and z is the desired depth.

Equivalent single axle load

Vehicles can have many axles which will distribute the load into different axles,

and in turn to the pavement through the wheels. A standard truck has two axles, front axle

with two wheels and rear axle with four wheels. But to carry large loads multiple axles

are provided. Since the design of flexible pavements is by layered theory, only the wheels

on one side needed to be considered. On the other hand, the design of rigid pavement is

Smartworld.asia 87


by plate theory and hence the wheel load on both sides of axle need to be considered.

Legal axle load:

Repetition of axle loads:

The deformation of pavement due to a single application of axle load may be small

but due to repeated application of load there would be accumulation of unrecovered or

permanent deformation which results in failure of pavement.

Equivalent axle load factor:

An equivalent axle load factor (EALF) defines the damage per pass to a pavement

by the ith type of axle relative to the damage per pass of a standard axle load. While

_finding the EALF, the failure criterion is important. Two types of failure criteria‟s are commonly adopted: fatigue cracking and rutting. The fatigue cracking model has the

following form:

Where, Nf is the number of load repetition for a certain percentage of

cracking, _t is the tensile strain at the

bottom of the binder course, E is the modulus of elasticity, and f1; f2; f3 are

constants. If we consider fatigue

Smartworld.asia 88


cracking as failure criteria, and a typical value of 4 for f2, then:

Where, i indicate Ith

vehicle, and std indicate the standard axle. Now if we assume

that the strain is proportional to the wheel load,

Similar results can be obtained if rutting model is used, which is:

where Nd is the permissible design rut depth (say 20mm), s the compressive strain at the

top of the subgrade,

and f4; f5 are constants. Once we have the EALF, then we can get the ESAL as given

below. Equivalent single axle load, ESAL =

Where, m is the number of axle load groups, Fi is the EALF for ith

axle load group, and

ni is the number of passes of ith axle load group during the design period.

Example Let number of load repetition expected by 80 KN standard axle is 1000, 160

KN is 100 and 40 KN is 10000. Find the equivalent axle load. Solution:

Smartworld.asia 89


IRC method of design of flexible pavements

Design traffic

The method considers traffic in terms of the cumulative number of standard

axles (8160 kg) to be carried by the pavement during the design life. This requires the

following information:

1. Initial traffic in terms of CVPD

2. Traffic growth rate during the design life

3. Design life in number of years

4. Vehicle damage factor (VDF)

5. Distribution of commercial traffic over the carriage way.

Initial traffic

Initial traffic is determined in terms of commercial vehicles per day (CVPD). For

the structural design of the pavement only commercial vehicles are considered assuming

laden weight of three tones or more and their axle loading will be considered. Estimate of

the initial daily average traffic flow for any road should normally be based on 7-day 24-

hour classified traffic counts (ADT). In case of new roads, traffic estimates can be made

on the basis of potential land use and traffic on existing routes in the area.

Traffic growth rate

Traffic growth rates can be estimated

(i) by studying the past trends of traffic growth, and

(ii) By establishing econometric models. If adequate data is not available, it

is recommended that an average annual growth rate of 7.5 percent may be

adopted.

Design life

Smartworld.asia 90


For the purpose of the pavement design, the design life is defined in terms of the

cumulative number of standard axles that can be carried before strengthening of the

pavement is necessary. It is recommended that pavements for arterial roads like NH, SH

should be designed for a life of 15 years, EH and urban roads for 20 years and

other categories of roads for 10 to 15 years.

Vehicle Damage Factor

The vehicle damage factor (VDF) is a multiplier for converting the number of

commercial vehicles of different axle loads and axle configurations to the number of

standard axle-load repetitions. It is defined as equivalent number of standard axles per

commercial vehicle. The VDF varies with the axle configuration, axle loading, terrain,

type of road, and from region to region. The axle load equivalency factors are used to

convert different axle load repetitions into equivalent standard axle load repetitions. For

these equivalency factors refer IRC: 37 2001. The exact VDF values are arrived after

extensive field surveys.

Vehicle distribution

A realistic assessment of distribution of commercial traffic by direction and by lane is

necessary as it directly affects the total equivalent standard axle load application used in

the design. Until reliable data is available, the following distribution may be assumed.

Single lane roads: Traffic tends to be more channelized on single roads than two

lane roads and to allow for this concentration of wheel load repetitions, the design

should be based on total number of commercial vehicles in both directions

Two-lane single carriageway roads: The design should be based on 75 % of the

commercial vehicles in both directions.

Four-lane single carriageway roads: The design should be based on 40 % of the

total number of commercial vehicles in both directions.

Dual carriageway roads: For the design of dual two-lane carriageway roads

should be based on 75 % of the number of commercial vehicles in each direction.

For dual three-lane carriageway and dual four-lane carriageway the distribution

factor will be 60 % and 45 % respectively.

Smartworld.asia 91


Numerical example

Design the pavement for construction of a new bypass with the following data:

1. Two lane carriage way

2. Initial traffic in the year of completion of construction = 400 CVPD (sum of

both directions)

3. Traffic growth rate = 7.5 %

4. Design life = 15 years

5. Vehicle damage factor based on axle load survey = 2.5 standard axle per

commercial vehicle

6. Design CBR of subgrade soil = 4%.

Smartworld.asia 92


Rigid pavement design

Wheel load stresses - Westergaard's stress equation

The cement concrete slab is assumed to be homogeneous and to have uniform elastic

properties with vertical sub-grade reaction being proportional to the deflection.

Westergaard developed relationships for the stress at

interior, edge and corner regions, denoted as _i; _e; _c in kg/cm2 respectively and

given by the equation.

where h is the slab thickness in cm, P is the wheel load in kg, a is the radius of the wheel

load distribution in cm, l the radius of the relative stiffness in cm 29.1 and b is the radius

of the resisting section in cm

Smartworld.asia 93


Temperature stresses

Temperature stresses are developed in cement concrete pavement due to variation

in slab temperature. This is caused by (i) daily variation resulting in a temperature

gradient across the thickness of the slab and (ii) seasonal variation resulting in overall

change in the slab temperature. The former results in warping stresses and the later in

frictional stresses.

Warping stress

The warping stress at the interior, edge and corner regions, denoted as ά ti; ά te; ά tc in kg/cm2 respectively and given by the equation

Smartworld.asia 94


Frictional stresses

The frictional stress ά f in kg/cm2 is given by the equation

Where W is the unit weight of concrete in kg/cm2 (2400), f is the coefficient of sub

grade friction (1.5) and L is the length of the slab in meters.

Combination of stresses

The cumulative effect of the different stress give rise to the following thee critical cases

Summer, mid-day: The critical stress is for edge region given by α critical = α e + α te – αf

Winter, mid-day: The critical combination of stress is for the edge region given by α critical = α e+ α te + α f

Mid-nights: The critical combination of stress is for the corner region given by α critical = α c + α tc

Smartworld.asia 95


UNIT 7 HIGHWAY CONSTRUCTION

Introduction

The science of highway engineering raises some fundamental questions as to what

is a road or highway, how is it planned and designed and lastly how is it built. By now in

the preceding chapters, Depending upon the desired strength of the pavement, the

aggregate gradations and the type and proportion of binders are decided. These three

basic binder medium give rise to a number of construction methods.

Types of Highway Construction

The highway types are classified as below:

(i) Earth road and gravel roads

(ii) Soil stabilized roads

(iii) Water bound macadam (WBM) road

(iv) Bituminous or black-top roads

(v) Cement concrete roads

The roads in India are classified based on location and functions. All the roads do not

cater for the same amount of traffic volume or intensity. Since the funds available at hand

for financing the construction projects are also meager, it is necessary to have roads which

cost less. The adoption of low cost roads is now preferred in developing countries like

India where large lengths of roads are to be constructed in the rural areas with the limited

finances available in the country. Earth roads and stabilized roads are typical examples of

low cost roads. Stabilized soil roads are gaining importance in the form of low cost roads.

EARTHWORK

General

The subgrade soil is prepared by bringing is to the desired grade and camber and

by compacting adequately. The subgrade may be either in embankment or in excavation,

depending on the topography and the finalized vertical alignment of the road to be

constructed.

Smartworld.asia 96


Excavation

Excavation is the process of cutting or loosening and removing earth including rock form

its original position. Transporting and dumping it as a fill or spoil bank. The excavation

or cutting mat is needed in soil, soft rock or even in hard rock, before preparing the

subgrade.

Embankment

When it is required to raise the grade line of a highway above the existing ground

level it becomes necessary to construct embankments. The grade line may be raised due

to any of the following reasons

i) To keep the subgrade above the high ground water table.

ii) To prevent damage to pavement due to surface water and capillary water.

iii) To maintain the design standards of the highway with respect to the Vertical

alignment.

The design elements in highway embankments are:

i) Height

ii) Fill material

iii) Settlement

iv) Stability of foundation, and

Stability of slopes

Height

The height of the embankment depends on the desired grade line of the highway and the

soil profile or topography. Also the height of the fill is some times governed by stability

of foundation, particularly when the foundation soil is weak.

Smartworld.asia 97


Fill Material

Granular soil is generally preferred as highway embankment material. Silts, and

clays are considered less desirable. Organic soils, particularly peat are unsuitable. The

best of the soils available locally is often selected with a view to keep the lead and lift as

low as possible. At times light-weight fill material like cinder may be used to reduce the

weight when foundation soil is weak.

Settlement

The embankment may settle after the completion of construction either due to

consolidation and settlement of the foundation or due to settlement of the fill or due to

both. If the embankment foundation consists of compressible soil with high moisture

content, the consolidation can occur due to increase in the load. The settlement of the fill

is generally due to inadequate compaction during construction and hence by proper

compaction this type of settlement may be almost eliminated. Whatever be the type of

settlement, it is desirable that the settlement is almost complete before the construction of

pavement.

Stability of Foundation

When the embankment foundation consists of weak soil just beneath or at a certain

depth below in the form of a weak stratum, it is essential to consider the stability of the

foundation against a failure. This is all the more essential in the case of high

embankments. The foundation stability is evaluated and the factor of safety is estimated

by any of the following approaches:

(b) Estimating the average shear stress and strength at the foundation layers by

approximate methods and estimating the factor of safety.

(c) Using theoretical analysis based on elastic theory.

The factor of safety in the case of compressible soil foundation is likely to be

minimum just after the completion of the embankment. Later due to consolidation of

foundation and consequent gain in strength there will be an increase in the foundation

factor of safety.

Stability of Slopes

The embankment slopes should be stable enough to eliminate the possibility of a

failure under adverse moisture and other conditions. Hence the stability of the slope

Smartworld.asia 98


should be checked or the slope should be designed providing minimum factor of safety of

1.5. Often much flatter slopes are preferred in highway embankments due to aesthetic and

other reasons.

Construction of embankments

The embankment may be constructed either by rolling in relatively thin layers or

by hydraulic fills. The former is called rolled-earth method and is preferred in highway

embankments. Each layer is compacted by rolling to a satisfactory degree or to a desired

density before the next layer is placed.

Preparation of Subgrade

The preparation of subgrade includes all operations before the pavement structure

could be laid over it and compacted. Thus the preparation of subgrade would include site

clearance, grading (embankment or cut section) and compaction. The subgrade may be

situated on embankment or excavation or at the existing ground surface. In all the cases,

site should be cleared off and the top soil consisting of grass roots rubbish and other

organic matter are to be removed. Next, the grading operation is started so as to bring the

vertical profile of the subgrade to designed grade and camber. Bull dozers, scrapers and

blade graders are useful equipment to speed up this work. It is most essential to compact

the top of

Soil Compaction

By compaction of soil, the particles are mechanically constrained to be packed

more closely, by expelling part of the air voids. Compaction increases the density and

stability, reduces settlement and lowers the adverse effects of moisture. Hence proper

compaction of fills, subgrade, sub-base and base course are considered essential for

proper highway construction.

The various factors influencing soil compaction include the moisture content, amount and

type of compaction, soil type and stone content. It is a well known fact that there is an

optimum moisture content (OMC) for a soil which would give maximum dry density for

a particular type and amount of compaction. Hence it is always desirable to compact the

soil at the OMC after deciding the compacting equipment.

Compacting equipment

Soil compaction is achieved in the field either by rolling, ramming or by vibration.

Hence the compacting equipment may also be classified as rollers, rammers and vibrators.

Smartworld.asia 99


Compactions of sands are also achieved by watering ponding and jetting.

Rollers

The principle of rollers is the application of pressure, which is slowly increased

and then decreased. The various type of rollers which are used for compaction are smooth

wheel, pneumatic tyred and sheep foot rollers. Further the construction equipment such as

trucks, tractors and bull dozers also help in compaction of the materials to some extent.

CONSTRUCTION OF EARTH ROADS

General

An earth road is the cheapest type of road prepared from natural soil. The pavement

sections is totally made out of the soil available at site and at near-by borrow pits. The

type of construction by and large, depends upon the type of soil at site.

keep the pavement surface free of standing water; otherwise the soil being Previous, the

water would damage the pavement section by softening it. The maximum cross slope of 1

in 20 is recommended to avoid erosion due to rain waters and formation of cross ruts.

Specification of Materials

Soil of the following properties is considered satisfactory for constructing earth roads:

Base Course Wearing course

Clay content < 5% 10 to 18%

Silt content 9 to 32% 5 to 15%

Sand Content 60 to 80% 60 to 80%

Liquid limit <35% <35%

Plasticity index <6% 40 to 10%

Smartworld.asia 100


Construction Procedure

The construction of earth road may be divided into the following steps:

Material. The soil survey is carried out and suitable borrow pits are located within

economical haulage distances. The borrow pits are usually selected outside the land

width. The trees, shrubs, grass roots and other organic matter including top soil a

removed before excavating earth for construction.

Location. The centre line and road edges are marked on the ground along the

alignment, by driving wooden pegs. Reference pegs are also driven to help in

following the desired vertical profile of the road during construction. The spacing of

the reference pegs depends on the estimated length of road construction per day

c) Shaping of subgrade.

The site clearance may be carried out manually using appliances like spade, pick and

shovel. Mechanical equipment like dozer, scraper and ripper may also be used for the

purpose. Construction of fills and excavation of costs to bring the road profile to the

desired grade may also be done either manually or using excavation, hauling and

compaction equipment.

Pavement construction. The borrowed soil (more than one soil type mixed to the

desired proportion, if necessary) is dumped on the prepared subgrad and pulverized. The

field moisture content is checked and additional water is added, if necessary, to bring it

upto OMC. light compaction is considered desirable. The camber of the finished

pavement surface is checked and corrected if necessary.

Opening to traffic. The compacted earth road is allowed to dry out for a few days

before opening to traffic.

CONSTRUCTION OF GRAVEL ROADS

General

Gravel roads are considered superior to earth roads as they can carry heavier

traffic. The road consists of a carriageway constructed using the gravels. The camber mat

be between I in 25 and 1 in 30. A well compacted crushed rock or gravel road is fairly

resilient and does not become slippery when wet.

Smartworld.asia 101


Material

Hard variety of crushed stone or gravel of specified gradation is uses. However

Varieties of Stone may also be utilized. There are no specifications for the mal Rounded

stones and river gravel are not preferable as there is poor interlocking.


Material Gravel to be used for the construction is stacked along the sides of theproposed

road.

Preparation of subgrade. Site is cleared and fills and cuts are completed. Trench

isformed to the desired depth of construction. The width of the trench is made equal to

that of the carriageway. The trench is brought to the desired grade and is compacted.

Pavement construction. Crushed gravel aggregates are placed carefully in the trenchso

as to avoid segregations. Aggregates are spread with greater thickness at centre and less

towards the edges so as to obtain the desired camber. The layer is rolled using smooth

wheeled rollers starting from the edges and proceeding towards the centre with an

overlap of atleast half the width of roller in the longitudinal direction. Some quantity of

water may also be sprayed and rolling is done again s that the compaction is effective.

The camber is checked and corrected from time to time using a template or camber

board.

Opening to traffic. A few days after the final rolling and drying out, the road

isopened to the traffic.

CONSTRUCTION OF WATER BOUND MACADAM ROADS

General

The Water bound macadam (WBM) is the construction known after the name of

John also article 2.16 and 2.17. The term macadam in the present day means, the

pavement base course made of crushed or broken aggregate mechanically interlocked by

rolling and the voids filled with screening and binding material with the assistance of

water.

Specifications of Materials for WBM Pavement

Coarse Aggregates

Smartworld.asia 102


The coarse aggregate used in WBM generally consists of hard varieties of crushed

aggregates or broken stones. However, soft aggregates like over burnt bricks metal or

naturally occurring soft aggregates such as kankar or laterite may be used. Crushed slag

obtained from blast furnace may also be used

Property Requirements for Pavement layer

Sub-base Base Course Surfacing course

(i) Los Angeles abrasion 60 50 40

(maximum value, percent)

or

(ii) Aggregate impact 50 40 30


(iii) Flakiness index - 15 15


Properties of Coarse Aggregates

The crushed stone aggregate should be generally hard, durable and free from

flaky and elongated particles. The IRC specifies the following ph requirement of

coarse aggregates for WBM construction, in terms of the test value the three

pavement layers.

Size and Grading Requirements of Coarse Aggregates

The coarse aggregates for each layer of construction should, as far as

possible conform to any one of the three gradings specified below. Grading No.1.

consists of Coarse aggregates of size range 90 to 40 mm and is more suitable for

sub-base course. Thickness of compacted layer is usually 100 mm. Grading No. 2

Smartworld.asia 103


consists of aggregates size range 63 to 40 mm and grading No. 3 of range 50 to 20

mm and compacted thickness of each layer is normally 75 mm..

Binding material consisting of fine grained material is used in WBM construction

to prevent raveling of the stones Kankar nodules or lime stone dust may also be utilized,

if locally available. The binding material with plasticity index value 4 to 9% is used in

WBM surface course construction; the plasticity index of binding course material should

be less than 6.0% in the case of WBM layers used as base course or sub-base course, with

bituminous surfacing. If the screenings used consist of crushable material like moorum or

soft gravel, there is no need to apply binding material, unless the plasticity index value is

low.

Quantity of Materials

The approximate loose quantities of materials required in m3 for 10 cm compacted

thickness of WBM sub-base using coarse aggregate of grading no I per 10 m2 area

are:

(a) Coarse aggregate size 90 to 40 mm = 1.21 to 1.43

(b) Stone screening type A, 12.5 mm size = 0.40 to 0.44

or

Crushable type screenings (moorum/gravel) = 0.44 to 0.47

(c) Binding material for sub-base course = 0.88 to 0.10

The approximate loose quantities of materials required in m3 for 7.5 cm compacted

thickness of WBM base course or surfacing course using coarse aggregate of

grading No. 2 per 10 m2 area are:

(a) Coarse aggregate size 63 to 40mm = 0.91 to 1.07

(b) Stone screening type A, 12.5 mm size for base course = 0.18 to 0.21

Stone screenings for surfacing course = 0.15 to 0.17

Alternatively, Stone screenings type B,

9.0 mm size for base course = 0.30 to 0.33

9.0 mm size for surfacing = 0.24 to 0.26

Alternatively, crushable type screenings = 0.33 to 0.35

(c) Binding material for base course = 0.06 to 0.09

Binding material for surfacing course = 0.10 to 0.15

(Note: Binding material is not required if crushable type of screening is used).

Smartworld.asia 104



Preparation of Foundation for Receiving the WBM course

The foundation for receiving the new layer of WBM may be either the subgrade or

sub-base or base course. This foundation layer is prepared to the required grade and

camber and the dust and either loose materials are cleaned. On existing road surface, the

depressions and pot-holes are filled and the corrugations are removed by scarifying and

reshaping the surface to the required grade and camber as necessary. If the existing

surface is a bituminous surfacing, ftirrows of depth 50 mm and width 50 mm cut at 1.0 m

intervals and at 45 degrees to the centre line of the carriageway before laying the Coarse

aggregate.

Provision of Lateral confinement

Lateral confinement is to be provided before starting WBM construction. This may

be done by constructing the shoulders to advance, to a thickness equal to that of the

compacted WBM layer and by trimming the inner sides vertically

Spreading of Coarse Aggregates

The coarse aggregates are spread uniformly to proper profile to even thickness

upon the prepared foundation and checked by templates. The WBM course is normally

constructed to compacted thickness of 7.5 cm except in the case of WBM sub-base course

using coarse aggregate grading no.1 which is of 10.0 cm compacted thickness.

Rolling

After spreading the coarse aggregates properly, compaction is done by a three

wheeled power roller of capacity 6 to 10 tons or alternatively by an equivalent vibratory

roI1q the weight of the roller depends on the type of coarse aggregates.

Application of Screenings.

After the coarse aggregates are rolled adequately, the dry screenings are

gradually over the surface to fill the interstices in three or more applications

Sprinkling and Grouting

After the application of screenings, the surface is sprinkled with water, swept

Smartworld.asia 105


rolled. Wet screenings are swept into the voids using hand brooms. Ad• screenings are applied and rolled till the coarse aggregates are well bonded and firmly set.

Application of Binding Material

After the application of screening and rolling, binding material is applied at a

uniform and slow rate at two or more successive thin layers. After each application of

binding material, the surface is copiously sprinkled with water and wet slurry swept with

brooms to fill the voids.

Setting and Drying

After final compaction, the WBM course is allowed to set over-night. On the next

day the „hungry‟ spots are located and are filled with screenings or binding material,

lightly sprinkled with water if necessary and rolled. No traffic is allowed till the WBM

layer sets and dries out.

Checking of Surface Evenness and Rectification of Defects

The surface evenness of longitudinal direction is checked by 3.0 m straight edge

and the number of undulations exceeding 12mm in the case if WBM layer of grading no.

1 and 10mm in the case of grading nos. 2 and 3 are recorded in each completed length of

300m; the maximum number of undulations permitted in each case in 30. The spots with

15mm undulations are marked for rectification of defects.

CONSTRUCTION OF BITUMINOUS PAVEMENTS

Introduction

Bituminous pavements are in common use in India and abroad. It is Possible

to construct relatively thin bituminous pavement layers over an existing Pavement

stages by constructing bituminous pavement layers one after another in a certain period of

time unlike the cement concrete pavement construction

Types of Bituminous Construction

Number of types and methods are in use for bituminous pavement construction. It

is attempted to broadly classify them here based on the methods of construction. The

following construction techniques are in use:

Smartworld.asia 106


Interface treatment like prime coat and tack

coat Surface dressing and seal coat

Grounted or penetration type constructions :

a) Penetration macadam b) Built-up spray Grout.

Premix which may be any of the following:

a) Bituminous bound macadam b) Carpet c) Bituminous concrete d) Sheet asphalt or rolled asphalt e) Mastic asphalt

Explanatory Notes on Bituminous Construction Types

Interface Treatment

Thus surface of the existing pavement layer is to be cleaned to remove dust and dir

and a thin layer of bituminous binder is to be sprayed 1.

Prime coat: Bituminous prime coat is the first application of a low viscosity

liquidbituminous material over an existing porous or absorbent pavement surface like the

WBM base course.

Tack coat. Bituminous tack coat is the application of bituminous material over existing

pavement surface which is relatively impervious like an existing bituminous surface or a

cement concrete pavement or a pervious surface like the WBM which has already been

treated by a prime coat.

Bituminous Surface Dressing

Bituminous Surface Dressing (BSD) is provided over an existing pavement to

serve as thin wearing coat. The single coat surface dressing consists of a single

application of bituminous binder material followed by spreading of aggregate cover and

rolling. When the surface dressing is similarly done in two layers, it is called „two coat

Smartworld.asia 107


bituminous surface dressing‟.

Seal Coat

Seal coat is usually recommended as a top coat over certain bituminous

pavements which are not impervious, such as open graded bituminous constructions like

premixed carpet and grouted Macadam. Seal coat is also provided over an existing

bituminous pavement which is worn out.:

(a) To seal the surfacing against the ingress of water

(b) To develop skid resistant texture

(c) To enliven an existing dry or weathered bituminous surface.

Penetration Macadam

Bituminous Penetration Macadam or Grouted Macadam is used as a base or binder

course. The coarse aggregates are first spread and compacted well in dry state and

after that hot bituminous binder of relatively high viscosity is sprayed in fairly large

quantity at the top

Premix Methods

In this group of methods the aggregates and the bituminous binder are mixed

thoroughly before spreading and compacting. It is possible to coat each particle of

aggregate with the binder still the quantity of binder used may be considerably lesser than

penetration macadam type construction. In premixed constructions, the quantity of

bitumen used could be precisely controlled and they offer increased stability of the mix

even with lower bitumen contents.

Bituminous Macadam

Bituminous Macadam (BM) or Bitumen Bound Macadam is a premixed

construction method consisting of one or more courses of compacted crushed aggregates

premixed with bituminous binder, laid immediately after mixing. The BM is laid in

compact thicknesses of 75 mm or 50 mm and three different gradations of aggregates

have been suggested for each thickness to provide open graded and semi-dense

constructions.

Smartworld.asia 108


Bituminous Premixed Carpet

Premixed Carpet (PC) consists of coarse aggregates of 12.5 and 10.0 mm sizes,

premixed with bitumen or tar binder are compacted to a thickness of 20 mm to serve as a

surface course of the pavement. Being a open graded construction, the PC is to be

invariably covered by a suitable seal coat such as premixed sand-bitumen seal coat before

opening to traffic. The PC consists of all aggregates passing 20 mm and retained on

6.3mm sieve. When a fairly well graded material as per specification is used for the

construction of the bituminous carpet of thickness 20 o 25 mm, the construction method

is called semi-dense carpet.

Bituminous Concrete or Asphalt Concrete

Bituminous Concrete or Asphaltic Concrete (AC) is a dense graded premixed

bituminous mix which is well compacted to form a high quality pavement surface Course.

The AC consists of a carefully proportioned mixture of coarse aggregates fine aggregates,

mineral filler and bitumen and the mix is designed by an appropriate method such as the

Marshall method to fulfil the requirements of stability, density, flexibility and voids. The

thickness of bituminous concrete surface course layer usually ranges from 40 to 75 mm.

The IRC has provided specification for 40 mm thick AC surface course for highway

pavements.

Sheet Asphalt

Sheet asphalt or rolled asphalt is a dense sand-bitumen premix of compacted

thickness 25 mm, used as a wearing course. The sheet asphalt consists of well graded

coarse to fine sand (without coarse aggregates) and a suitable penetration grade bitumen

to from a dense and impervious layer. This is usually laid over cement concrete pavement

to provide an excellent riding surface. The sheet asphalt also protects the joints in cement

concrete pavements and could cause a reduction in warping stresses due to a decrease in

the temperature variations between top and bottom of the concrete slab.

Mastic Asphalt

Mastic asphalt is a mixture of bitumen, fine aggregates and filler in suitable

proportions which yields a voidless and impermeable mass. Though the ingredients in

mastic asphalt are similar to those in bituminous concrete, properties of mastic asphalts

Smartworld.asia 109


are quite different. The mastic asphalts when cooled results in a hard, stable and durable

layer suitable to withstand heavy traffic. This material also can absorb vibrations and has

property f self-healing of cracks without bleeding. It is a suitable surfacing materials for

bridge deck slabs.

Construction Procedure for Bituminous Macadam

The Bituminous Macadam (BM) bitumen bound macadam is a premix laid

immediately after mixing and then compacted. It is an open graded construction suitable

only as a base or binder course. When this layer is exposed as a surface course, at least a

seal coat is necessary.

Specifications of Materials:

The grades of bitumen used are 30/40, 60/70 and 80/100 penetration. Road tar RT-

4, cutback and emulsion can also be used in cold mix construction technique. The binder

content used varies from 3.0 to 4.5 percent by weight of the mix). Aggregates used are of

low porosity fulfilling the following requirements for the base Course.

Los Angle abrasion value 50 percent max.

Aggregate impact value 35 percent max.

Flakiness index 15 percent max.

Stripping at 40°C after 24 hours immersion (CRRI test) 25 percent max.

Loss with sodium sulphate, 5 cycles 12 percent max.

For binder course the specified maximum abrasion and impact values are 40 and

30 percent respectively.

The grading of the aggregates for 75 mm and 50 mm thickness for base and binder

course instruction as specified by Indian Roads Congress are given in Table 8.4 (a) &

respectively. The quantity of aggregates required for 10 m2 of bitumen bound macadam

are 0.60 to 0.75 m3 and 0.90 to 1.0 m3 respectively, for 50 and 75 mm compacted

thickness. The bitumen quantity would be determined based on the grading adopted as

specified above.

Smartworld.asia 110


Constructions Steps

Preparation of existing layer: The existing layer is prepared to a proper profile. Pot

holes are patched and irregularities are made even. The surface is properly cleaned.

Tack coat or prime coat application: A track coat is applied of thin layer of bitumen

binder on the existing layer either using the sprayer or a pouring can. the quantity of

application is 40 to 7.5 kg per 10 m2 for black top layer and 7.5 to 10kg per 10 m2 for

untreated WBM layer.

Premix preparation: The bitumen binder and aggregates as per recommended

gradingsare separately heated to the specified temperatures and are then placed in the

mixer

chosen for the job. The mixing temperature for each grading and the bitumen binder is

also specified based on. the laboratory results. A tolerance of ± 10°C is allowed. The

mixing is done till a homogeneous mixture is obtained. The mixture is then carried to

the site for its placement through a transporter or a wheel barrow.

Placement. The bituminous paving mixture is then immediately placed on the

desiredlocation and is spread with rakes to a pre-determined thickness. The camber

profile is checked with a template. It may be stated here that a compacting

temperature also influences the strength characteristic of the resulting pavement

structure. It is therefore required that the minimum time is spent between the

placement of the mix and the rolling operations.

Rolling and finishing The paving mix. The rolling is done with 8 to 10 tones

tandemroller. The rolling is commenced from the edges of the pavement construction

towards the centre, and uniform overlapping is provided. The finished surface should

not show separate lines of markings due to defective or improper rolling. The roller

wheels are kept damp, otherwise the paving mix may partly stick to the wheels and the

finishing may not be good. A variation of 6 mm over 3 m length is allowed in the

cross profile. The number of undulations exceeding 10 nun should be less than 30 in

300 m length of pavement.

Construction Procedure for Bituminous Concrete

The bituminous concrete is the highest quality of construction in the group of

black top surface. Being of high cost specifications, the bituminous mixes are properly

designed to satisfy the design requirements of the stability and durabi1ity. The mixture

contains dense grading of coarse aggregate, fine aggregate and mineral filler coated with

Smartworld.asia 111


bitumen binder. The mix is prepared in a hot-mix plant. The thickness of the bituminous

concrete layer depends upon the traffic and quality of base course.

The specifications of materials and the construction steps for bituminous concrete or

asphaltic concrete (AC) surface course are given below:

Specification of Materials:

a) Binder: Bitumen of grade 3 0/40,60/70 or 80/100 may be chosen depending Upon

tic

b) Aggregates and Filler: The coarse aggregates should fulfill the following

requirements

Aggregate impact value, maximum percent : 30

or Loss Angeles abrasion value, max percent : 40

Flakiness index, max percent : 25

Stripping at 40°C after 24 hours, max percent : 25

Soundness:

Loss with sodium sulphate in 5 cycles, max. percent : 12

Loss with magnesium sulphate in 5 cycles, max. percent : 18

The gradation of aggregates and filler should conform to those given in Table 8.5.

Smartworld.asia 112


Table 8.5 Gradation of Aggregates for Bituminous Concrete

Sieve Size, mm Percent passing by

weight

Grading 1 Grading 2

20.00 - 100

12.50 100 80-100

10.00 80-100 70-90

4.75 55-75 50-70

2.36 35-50 35-50

0.60 18-29 18-29

0.30 13-23 13-23

0.15 8-16 8-16

0.75 4-10 4-10

CONSTRUCTION OF CEMENT CONCRETE PAVEMENTS

Introduction

The Cement concrete pavement maintains a very high recognition among the

engineer and the road users alike. Due to the excellent riding surface and pleasing

appearance, the cement concrete roads are very much preferred.

Specifications of material for cement concrete pavement slabs.

The materials required for plain concrete slabs are cement coarse aggregates, fine

aggregates and water. In case reinforcement is provided, steel wire fabric or bar mats may

Smartworld.asia 113


be used of the required size and spacing. Other materials are for the construction of joints,

such as load transfer devices, joints filler and sealer.

Cement:

Ordinary portland cement is generally used. In case of urgency rapid hardening

cement may also be used to reduce curing time.

Coarse aggregates:

The maximum size of coarse aggregates should not exceed one fourth the slab

thickness. The gradation of coarse aggregate may range from 50 to 4.75 mm or 40 to 4.75

mm, the aggregate is collected in two size ranges, one below and the other above 20mm

size. When the grading is from 20 to 50 mm, the materials are collected in two groups,

below and above 25 mm size.:

Fine aggregate.

Natural sands should be preferred as fine aggregate though crushed Stones may

also be used.

Proportioning of concrete.

The concrete may be proportioned so as to obtain a minimum modulus of rupture

of 40 kg/cm2 on field specimens after 28 days curing or to develop a minimum

compressive strength of 280 kg/cm2 at 28 days, or higher value as desired in the design.

Plants and Equipment

The equipment necessary for the construction of cement concrete slabs are for

batching, placing, finishing and carrying the concrete pavement. Equipment commonly

used are given below.

Concrete Mixer:

If batching by volume is required then the separate measuring boxes are provided

for the different aggregates. Each box is provided with a straight edge for striking off

excess material after filling.

Batching Device

Smartworld.asia 114


Concrete mixer of adequate capacity of the batch type is provided. It has a rated

capacity of not less than 0.2 m3 of mixed concrete. The mixture is equipped with a water

measuring device capable of accurate measurement of water required per batch. Some

mixtures are also equipped with timing devices which automatically lock the discharge

lever during the full time of mixing and releases it at the end of mixing period.

Wheel Borrow

Wheel borrows with two wheels are used to transport concrete for short distances

from the mixer.

Vibrating Screed

Vibrating screed comprises of a wooden or mild steel screed with suitable handles

driven by vibrating units mounted thereon, propelled either electrically or by compressed

air or by a petrol engine, and travelling on side forms.

Internal Vibrators

It comprises of vibrating head with suitable motive power either of compressed air,

electricity or of a petrol driven engine right enough to ensure proper control and

manipulation in the mass of concrete. It is used to ensure compaction of the cement

concretealong with the forms and also to avoid any tendency of honey-combing at the

edges of the slab.

Tools and appliances for surface, finishing operations in common use are float,

straight edge, belt and fiber brush.

Float

The longitudinal float is of 75 cm length and 7.5 cm width and is made of hard

wood and is fixed with handle. (See Fig. 8.15). This is used for smoothing the concrete.

Straight Edge:

It is used to check the finished pavement surface in longitudinal direction. It is

made of hard wood with M.S. plate at bottom, 3 meter in length, 10 cm in width with two

handles as shown in Fig. 8.16.

Smartworld.asia 115


Belt:

Canvas belts are used for finishing the pavements surface before the concrete

hardens. The canvas is of 25 cm width and atleast 75 cm longer than the width of

pavement slab. It has two wooden handles at the end. See Fig. 8.17.

Fibre Brush:

Fibre brush broom is used to make broom marks across the pavement surface and

to make it skid resistance. Hard fibres are used projecting out of the wooden bursh of

length 45cm and width 7.5 cm, with a handle about 2 meter long.

Edging Tool

The edging tool is used for rounding the transverse edges at expansion joints and

the longitudinal edges. The vertical limb of this tool extends to the required depth. The

rounded edge of the M.S. plate has radius f 6 mm.

Other Small Tools

Other small tools d equipment such as spades, shovels and pans water pots etc.

necessary for the work are also provided.

Construction steps for cement concrete pavement slab

(i) Preparation of Subgrade and Sub-base

The subgrade or sub-base for laying of the concrete slabs should comply with the

wing requirement; that no soft spots are present in the subgrade or sub-base; that the

uniformly compacted subgrade or sub-base extends atleast 30 cm on either side of the

width to be concreted; that the subgrade is properly drained; that the minimum modulus

subgrade reaction obtained with a plate bearing test is 5.54 kg/cm2.

over the soil subgrade. In such a case, the moistening of the subgrade prior to

placing of the concrete is not required.

(iii) Batching of Material and Mixing

After determining the proportion of ingredients for the field mix, the fine

aggregates and coarse aggregates are proportioned by weight in a weight-batching plant

and placed into the hopper along with the necessary quantity of cement. Cement is

Smartworld.asia 116


measured by the bag. All batching of material is done on the basis of one or more whole

bags of cement.

(iv) Transporting and Placing of Concrete

The cement concrete is mixed in quantities required for immediate use and is

deposited on the soil subgrade or sub-base to the required depth and width of the

pavement section within the form work in continuous operation.

(v) Compaction and Finishing

The surface of pavement is compacted either by means of a power-driven finishing

machine or by a vibrating hand screed. For areas where the width of the slab is

very small as at the corner of road junctions, etc., hand consolidation and finishing

may be adopted:

(a) Concrete as soon as placed, is struck off uniformly and screeded to the

crown and cross-section of the pavement to conform the grade.

(b) The tamper is placed on the side forms and is drawn ahead in combination

with a series of lifts and drops to compact the concrete.

Floating and Straight Edging

The concrete is further compacted by means of the longitudinal float. The

longitudinal float is held in a position parallel to carriageway centre line and passed

gradually from one side of the pavement to the other. After the longitudinal floating is

done and the excess water gets disappeared, the slab surface is tested for its grade and

level with the straight edge.

Smartworld.asia 117


HIGHWAY DRAINAGE

INTRODUCTION

Highway drainage is the process of removing and controlling excess surface and

sub-soil water within the right of way this includes interception and diversion of water

from the road surface and subgrade. The installation of suitable surface and sub-surface

drainage system is an essential part of highway design and construction.

IMPORTANCE OF HIGHWAY DRAINAGE

Significance of Drainage

An increase in moisture content causes decrease in strength or stability of a soil

mass the variation in soil strength with moisture content also depends on the soil type and

the mode of stress application. Highway drainage is important because of the following

reasons:-

Excess moisture in soil subgrade causes considerable lowering of its stability the

pavement is likely to fail due to subgrade failure as discussed in Article 10.1.

Increase in moisture cause reduction in strength of many pavement materials like

stabilized soil and water bound macadam.

In some clayey soils variation in moisture content causes considerable variation in

flume of subgrade. This sometimes contributes to pavement failure.

One of the most important causes of pavement failure by the formation of waves and

corrugations in flexible pavements is due to poor drainage.

Sustained contact of water with bituminous pavements causes failures due to stripping

of bitumen from aggregates like loosening or detachment of some of the bituminous

pavement layers and formation of pot holes.

In places where freezing temperatures are prevalent in winter, the presence of water in

the subgrade and a continuous supply of water from the ground water can cause

considerable damage to the pavement due in frost action.

Smartworld.asia 118


Requirements of Highway Drainage System

The surface water from the carriageway and shoulder should effectively be drained off

without allowing it to percolate to subgrade.

The surface water from the adjoining land should be prevented from entering the

roadway. The side drain should have sufficient capacity and longitudinal slope to carry

away all the

surface water collected.

Flow of surface water across the road and shoulders and along slopes should not cause

formation of cress ruts or erosion.

SURFACE DRAINAGE

The surface water is to be collected and then disposed off. The water is first

collected in longitudinal drains, generally in side drains and then the water is disposed off

at the nearest stream, valley or water course. Cross drainage structures like culverts and

small bridges may be necessary for the disposal of surface water from the road side

drains.

Collection of Surface Water

The water from the pavement surface is removed by providing the camber or cross

slope to the pavement. The rate of this cross slope is decided based on type of pavement

surface and amount rainfall.

where there is restriction of space, Construction of deep open drains may be undesirable.

This is particularly true when the road formation is in cutting. In such cases covered

drains or drainage trenches properly filled with layers of coarse sand and gravel may be

used. In urban roads because of the limitation of land width and also due to the presence

of foot path, dividing islands and other road facilities, it is necessary to provide

underground longitudinal

drains. Water drained from the pavement surface can be carried forward in the longitudinal

direction between the kerb and the pavement for short distances (See Fig. 4.9). This water

may be collected in catch pits at suitable intervals and lead through underground drainage

pipes. Section of a typical catch pit with grating to prevent the entry of rubbish into the

Smartworld.asia 119


drainage system.

Drainage of surface water is all the more important in hill roads. Apart from the

drainage of water from the road formation, the efficient diversion and disposal of water

flowing down the hill slope across the road and that from numerous cross streams is an

important part of hill road construction. If the drainage system in hill road is not adequate

and efficient, it will result in complex maintenance problems.

Design of Surface Drainage System

The design of surface drainage system may be divided into two phases:

(i) Hydrologic analysis

(ii) Hydraulic analysis

Once the design runoff Q is determined, the next step is the hydraulic design

of drains. The side drains and partially filled culverts are designed based on the

principles of flow through open channels.

Data for Drainage Design

The following data are to be collected for the design of road side drain:

Total road length and width of land from where water is expected to flow on the stretch

of the side drain.

Run-off coefficients of different types of surfaces in the drainage area and their respective

areas (such as paved area, road shoulder area, turf surface, etc.)

Designed Steps

Simplified steps for the design of longitudinal drains of a road to drain off the

surface water given below:

The frequency of return period such as 10 years, 25 years etc. is decided based on

finances available and desired margin of safety, for the design of the drainage system.

The values of coefficients of run-off C1, C2, C3 etc. from drainage areas A1, A2, A3

Smartworld.asia 120


etc. are found and the weighted value of C is computed.

Inlet time for the flow of storm water from the farthest point in the drainage area

to the drain inlet along the steepest path of flow is estimated from the distance, slope of

the ground and type of the cover. Figure 11.3 may be used for this purpose.

Time of flow along the longitudinal drain T2 is. determined for the estimated length of

longitudinal drain L upto the nearest cross drainage or a water course and for the

allowable velocity of flow V in the drain i.e., T2 = L.

The total time T for inlet flow and flow along the drain is taken as the time of

concentration or the design value of rain fall duration, T = T1 + T2.

The required depth of flow in the drain is calculated for a convenient bottom width

and side slop of the drain. The actual depth of the open channel drain may be increased

slightly to give a free board. The hydraulic mean radius of flow R is determined.

The required longitudinal slope S of the drain is calculated using Manning‟s formula adopting suitable value of roughness coefficient n.

drain in a sandy clay soil from the inlet point to the cross drainage is 540m. The velocity

of flow in the side drain may be assumed as 0.6 rn/sec so that silting and erosion are

prevented. Estimate the design quantity of flow on the side drain for a ten-years period

of frequency of occurrence of the storm.

Cross Drainage

Whenever streams have to cross the roadway, facility for cross drainage is to be

provided. Also often the water from the side drain is taken across by these cross drain in

order to divert the water away from the road, to a water course or valley. The cross

drainage structures commonly in use are culveris and small bridges. When a small stream

crosses a road with a linear waterway less than about six meter, the cross drainage

structure provided is called culvert; for higher values of linear waterway, the structure is

called a bridge.

SURFACE DRAINAGE

Change in moisture content of subgrade are caused by fluctuations in ground water

table seepage flow, percolation of rain water and movement of capillary water and even

water vapour. In sub-surface drainage of highways, it is attempted to keep the variation of

moisture in subgrade soil to a minimum. However only the gravitational water is drained

by the usual drainage systems.

Smartworld.asia 121


Lowering of Water Table

The Highest level of water table should be fairly below the level of subgrade, in

order that the subgrade and pavement layers are not subjected to excessive moisture.

From practical considerations it is suggested that the water table should be kept atleast 1.0

to 1.2 m the subgrade. In places where water table is high (almost at ground level at

times) the best remedy is to take the road formation on embankment of height not less

than 1.0 to 1.2 meter. When the formation is to be at or below the general ground level, it

would be necessary to lower the water table.

Smartworld.asia 122


UNIT 8 HIGHWAY ECONOMICS & FINANCE

INTRODUCTION

Better highway system provides varied benefits to the society. Improvements in

highway results in several benefits to the road users such as :Reduction in vehicle

operational cost per unit length of road. saving travel time and resultant benefits in terms

of time cost of vehicles and the passengers Reduction in accident rates. Improved level of

service and ease of driving. Increased comfort to passengers. Therefore he level of service

of a road system may be assessed from the benefits to the users The improvement in road

net work also benefits the land owner by providing better access and consequently

enhancing the land value. The cost of improvements in the highway of land, materials,

construction work and for the other facilities should be worked out. From the point of view

of economic justification for the improvements, the cost reductions to the highway users

and other beneficiaries of the improvements during the estimated period should be higher

than the investments made for the improvement. In the planning and design of highways

there is increasing need for analysis to indicate justification of the expenditure required and

the comparative worth of proposed improvements, particularly when various alternatives

are being compared.

The government or any other agency finances highway developments. The funds for these

are generally recovered 1ins the road users in the form of direct and indirect taxations.

HIGHWAY USER BENEFITS

General Benefits

Several benefits are brought to highway users and others due to the construction of

a new highway or by improving a highway. Road user benefits are the advantages,

privileges or savings that accrue to drivers or owners through the use of one highway

facility as compared with the use of another. The various benefits due to highway

Smartworld.asia 123


improvement may be classified into two categories: (i) quantifiable or tangible benefits in

terms of market values and (ii) non quantifiable or intangible benefits.

Quantifilab1e Benefits

Various benefits which can be quantified include benefits to road user such as

reduction in vehicle operation cost, time cost and accident cost. The other benefits

include enhancement in land value. These are briefly explained below:

Saving in vehicle operation cost is due to reduction in fuel and oil consumption and

reduction in wear and tear of tyres and other maintenance costs. A road with sharp

curves and steep grades require frequent speed changes; presence of intersections

require stopping idling and accelerating; vehicle operation on road stretches with high

traffic volume or congestion necessitates speed changes and stopping and increased

travel time.

Non-quantable Benefits

The non-quantifiable benefits due to improvements in highway facilities include

reduction in fatigue and discomfort during travel, increase in comfort and conveniences

and improvement in general amenities, social and educational aspects, development of

recreational and medical services, improved mobility of essential services and defence

forces, aesthetic values, etc..

Motor Vehicle Operation Cost

The factors to be considered for evaluating motor vehicle operation cost would

differ depending on the purpose of the analysis. The vehicle may be classified in

different groups such as passenger cars, buses, light commercial vehicles, single unit

trucks combination vehicles etc., for the purpose of cost analysis. The motor vehicle

operation costs depend on several factors which may be grouped .as given below:

Cost dependent on time expressed as cost per year such as interest on capita

Smartworld.asia 124


depreciation cost, registration fee, insurance charges, garage rent, driver‟s license salaries etc. as applicable.

Cost depending on distance driven expressed as cost per vehicle-kilometer. The items

which may be included here are fuel, oil, tyres, maintenance and repairs etc.

Cost dependent on speed include cost of fuel, oil and tyre per vehicle-km-time-cost of

vehicles, travel time value of passengers, etc.

Cost dependent on type of vehicle and its condition. Operation costs of larger vehicles

are comparatively higher. The operation cost of old vehicles maintained in poor

condition is also higher.

Accident costs.

The costs of vehicle operation and time for unit distance may be taken as:

T = a+ (b+c) (14.1)

Speed

Where

a = running cost per unit distance, independent of journey time

b = a fixed hourly cost, dependent on speeds

c = the portion of the running cost which is dependent on speed

pavement surface and its condition, grades, curves and traffic volumes. Also the time

costs and accident costs are taken into consideration.

Example 14.1

Calculate the operating cost of a passenger car for 100 km length of a rural

highway with no sharp curves for most economical speed of vehicles operation using

the following

Smartworld.asia 125


HIGHWAY COSTS

General

The total Highway Cost for road user benefit analysis is the sum of the capital

costs expressed on an annual basis and the annual cost of maintenance. The total cost for

highway improvement is obtained from the estimate prepared from the preliminary plans.

The total cost of each highway engineering improvement proposal is calculated from the

following five components

(i) Right of way

(ii) Grading drainage, minor structures

(iii) Major structures like bridges

(iv) Pavement and appurtenances

(v) Annual cost of maintenance and operation

Computation of total annual highway cost based on summation of the annual cost of

individual items of improvements and their average useful lives is considered to be a

proper and accurate approach.It is difficult to estimate the service lives of highway

elements as there are several variables such as soil, climate topography and traffic. Road

life studies enable estimation of lives of pavements, bridges and other roadway facilities.

(i) Administration (a portion) Personal service, building, equipment operation,

office, insurance etc.

(ii) Highway operation Equipment. building vehicle operation including capital

costs of vehicle.

(iii) Highway maintenance

(iv) Highway capital cost : Cost of highway components such as right of way,

damage, earthwork, drainage system. pavement bridges and traffic services

depreciation cost and interest on investment.

(v) Probable life and salvage value at the end of this period.

The average annual highway cost for a road system may be summed up by

Smartworld.asia 126


the formula.

Ca – H + T + M + Cr

where

Ca = average annual cost of ownership and operation

H = average cost for administration and management at head quarters

T = average annual highway operation cost.

M = average annual highway maintenance cost.

Cr = average annual capital cost of depreciation of investment

capital or the capital recovery with return on capital

The annual cost is considered in the economic assessment of highway projects. Instead of

considering the overall cost of a project the annual repayment of a capital loan plus the

interest over a specified period of time of the annual capital cost is considered in the

analysis.

economical proposal among various alternatives, in the analysis for economic

justification of the proposed improvement, it is required to use judgment such as

quantitative selection of the factors in which annual highway cost depends and the

estimation of AADT of each class of vehicle considering the normal increase in traffic

and the generated traffic.

Methods of Analysis

The procedure for the economic evaluation of highway projects consists of

qualification for cost component and the benefits arising out of the project and to

evaluate by one of the methods of analysis.

There are several methods of economic analysis. Some of the common methods

are. Annual-cost Method, Rate-of-Return Method and Benefit-Cost Method.

Annual-Cost Method

The annual cost of each element of capital improvement is found by multiplying

Smartworld.asia 127


by the appropriate CRF value calculated for the assume life span. The annual cost Cr

may be found using the relation (Eq. 14.3).

C1 = P. i(1+i)n = P(CRF)

(1+i)n-1

Rate-of-Return Method

There are number of variations for the determination of raw of return of a

highway improvement. In the rate of return method, die interest rate at which two

alternative solutions have equal annual cost is found, If the rate of return of all proposed

projects are known, the priority for the improvement could be established.

Benefit Cost ratio Method

Principle of this method is to assess the merit of a particular scheme by comparing

the annual benefits with the increase in annual cost

Benefit cost ration = Annual benefits from improvement

Annual cost of the improvement

= R–R1

H1-H

Where R = total annual road user cost for axisting highway

R1 = total annual road user cost for proposed highway

improvement

H = total annual cost of existing road

H1 = total annual cost of proposed highway improvement

The benefit-cost ratios are determined between alternate proposals and those

plans dub are not attractive are discarded. Then the benefit cost ratios for various

increments of added investment are computed to arrive at the best proposal. hi order to

justify the proposed improvement, the ratio should be greater than 1.0. However, the

Smartworld.asia 128


choice of interest rate would affect the results of the benefit-cost solutions.

Total annual road user cost for proposal B = RB = Rs. 2491,125

Total annual highway cost of proposal C = HC = Rs.3,75,100

Total annual highway cost of proposal C= HC = Rs.2377,245

Benefit – cost ratio,

C = RA-RB = 3081,330 - 2377.245 = 704,085 = 3.546

A HC-HA 375,100 - 176,527 198, 573

Therefore, alternative C is the best one with higher benefit-cost ratio.

HIGHWAY FINANCE

Basic principle in highway financing is that the funds spent on highways

are recovered from the road users. The recovery may be both direct and indirect.

Two general methods of highway financing are:

Pay-as-you-go method

Credit financing method

In pay-as-you-go method, the payment for highway improvements, maintenance

and

operation is made from the central revenue. In credit financing method, the payment

for highway improvement is made from borrowed money and this amount and the

interests are

re-paid from the future income.

129

Transportation Engineering 1

Distribution of highway cost

The question of distributing highway cost among the Government, road-user and

other has been a disputed task in several countries. Many economists are of the view that

the financial responsibility for roads should be assigned only among the beneficiaries on

the basis of the benefit each one receives.

There are several theories suggesting the method of distribution of highway taxes

between passenger cars and other commercial vehicles like the trucks. However in India

the annual revenue from transport has been much higher than the expenditure on road

development and maintenance. Therefore there is no problem of distributing the highway

cost among other agencies. Also the taxation on vehicles is being considered separately

by the states and there seems to be no theory followed for the distribution of taxes

between various classes of vehicles.

Sources of Revenue

The various sources from which funds necessary for highway development

and maintenance may be made available, are listed below:

Taxes on motor fuel and lubricants.

Duties and taxes on new vehicles and spare part including tyres

Vehicles registration tax.

Special taxes on commercial vehicles

Other road user taxes

Property taxes

Toll taxes

Other funds set apart for highways

Highway financing in India

The responsibility of financing different roads lies with the Central Government,

State Governments and local bodies including Corporations, Municipalities, District

Boards and Panchayats.

130

Transportation Engineering 1

Taxes levied by Central Government for highway financing are:

Duties arid taxes on motor fuel

.Excise duty on vehicles and spare parts, tyre etc.

Excise duty on oils, grease, etc

Taxes levied by the State Governments include:

Registration fees for vehicles and road tax

Permits for transport vehicles

Passenger tax on buses

Sales tax on vehicle parts tyre etc.

Fees on driving licenses

Taxes levied by local bodies are mainly the toll tax.

Ever since the introduction of Central Road Fund (CRF) in the year 1929 by taxing motor

fuel, this has been the main source of finance for the State Government to meet the road

development needs, without having to go through the time consuming process of special

sanctions each time. However of late the CRF is also being merged with the general

revenue, in March 1976 the Lok Sabha has passed the resolution Of the Ministry of

Transport ensuring

department of civil enginnering

Documents