the use of geosynthetics in road construction

5/25/2018 The Use of Geosynthetics in Road Construction

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USE OF GEOSYNTHETICS IN ROAD CONSTRUCTION

(CASE STUDYGEOTEXTILE)

BY

ALAO, OLUKAYODE OLAWALE

CVE/06/7929

A PROJECT SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE

AWARD OF BACHELOR OF ENGINEERING (B.ENG.)

DEGREE IN CIVIL ENGINEERING

TO

THE DEPARTMENT OF CIVIL ENGINEERING

SCHOOL OF ENGINEERING AND ENGINEERING TECHNOLOGY

FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE

ONDO STATE

AUGUST, 2011


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CHAPTER ONE

INTRODUCTION

1.0 PREAMBLE

Geosynthetics have been defined by the American Society for Testing and Materials

(ASTM) Committee D35 on geosynthetics as planar products manufactured from polymeric

materials used with soil, rock, earth, or other geotechnical engineering related material as an

integral part of a man-made project, structure or system. Geosynthetics is the term used to

describe a range of polymeric products used for Civil Engineering construction works. The term

is generally regarded to encompass eight main products categories. They include geotextiles,

geogrids, geonets, geomembrane, geosynthetic clay liners, geofoam, geocells and geocomposite.

The most popular geosynthetics used are the geotextiles and geomembrane.

The ASTM (1994) defines geotextiles as permeable textile materials used in contact with

soil, rock, earth or any other geotechnical related material as an integral part of civil engineering

project, structure, or system.

Geomembrane is an essentially impermeable membrane in the form of manufactured

sheet used widely as cut-offs and liners. They are often used to line landfills.

Geotextiles, as permeable textile materials are used in contact with soil, rock, earth or any

other geotechnical related material as an integral part of civil engineering project, structure, or

system.

A geogrid is a polymeric structure, unidirectional or bidirectional, in the form of

manufactured sheet, consisting of a regular network of integrally connected elements which may


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be linked by extrusion, bonding, and whose openings are larger than the constituents and are

used in geotechnical, environmental, hydraulic and transportation engineering applications.

A geonet is a polymeric structure in the form of manufactured sheet, consisting of a

regular network of integrally connected overlapping ribs, whose openings are usually larger than

its constituents.

A geocomposite is an assembled polymeric material in the form of manufactured sheet or

strips, consisting of at least, one geosynthetic among the components, used in geotechnical

environmental and transportational engineering applications.

A geomat is a polymeric structure in the form of manufactured sheet consisting of non-

regular networks of fibres, yarns, filament, tapes or other elements which may be thermally or

mechanically connected and whose openings are larger than its constituents.

A geocell is a polymeric cellular structure consisting of regular open networks of

connected strips linked by extrusion or adhesion or other methods

Geotextiles have proven to be among the most versatile and cost-effective ground

modification materials. Their use has expanded rapidly into nearly all areas of civil,

geotechnical, environmental, coastal, and hydraulic engineering.


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1.1 AIM AND OBJECTIVES

The aim of this research work is to assess the different types of geosynthetics available and to

evaluate the effectiveness of the geotextile in road construction and maintenance. To achieve this

aim, the following objectives have been identified:

(1)To classify the available geosynthetics in the country.(2)To determine the constituent material used in producing the geotextile, one of the

geosynthetic materials.

(3)To incorporate the geotextile in some collected soil materials and assess performance.(4)To analyse the results and make appropriate recommendations for optimal use.

1.2 HYPOTHESISH0: Geotextiles is not among the most versatile and cost-effective ground modification and soil

stabilizing materials in the construction industry.

H1: Geotextiles is among the most versatile and cost-effective ground modification and soil

stabilizing materials in the construction industry.

1.3 JUSTIFICATION OF THE STUDY

The high rate of erosion and poor drainage system in different parts of the country has led to

speedy road degradation and extra costs incurred on road rehabilitation; hence the use of

geosynthetics is aimed at controlling this phenomenon. The benefits of a geosynthetic material in

any application are defined by six discrete functions: separation, filtration, drainage,

reinforcement, sealing and protection.


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The geotextile acts as a filter through which water passes while it restricts fine-grained soil from

entering into coarse-grained soil (sand or gravel) and thus prevent their being washed away and

forestall failure of the road.

1.4 SCOPE OF THE STUDY

This work shall be limited to the use of geosynthetics as a soil stabilizer in road construction. It

would involve the collection of soil materials and determination of their geotechnical properties

both soaked and unsoaked after which the geotextile would be incorporated into the soil sample

and their geotechnical properties also determined in both the soaked and unsoaked conditions.

The result would be analysed and the effect of the geotextile on the tested soil sample would be

evaluated and the appropriate recommendations would be made for their best use.


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CHAPTER TWO

LITERATURE REVIEW

2.0 CONCEPT OF GEOSYNTHETICS

In times past, various types of materials have been added to soil in order to increase its

stability, for use as an engineering construction material. But these materials such as plant fibres,

wood shavings and cotton are bio-degradable and therefore have short service life. In only a few

decades, geosynthetics (geotextiles, geogrids, and geomembranes) have joined the list of

traditional civil engineering construction materials.

With the advent of polymers in the middle of the 20th Century, a much more stable group

of materials became available. These groups of polymer materials, called geosynthetics, have

been employed in civil engineering works due to their stability and durability. Geosynthetics

were first employed in the 1960s as filters in the United States and as reinforcement in Europe.

Geosynthetics have been formulated and are available in a wide range of forms to suit various

engineering applications. Often the use of a geosynthetic can significantly increase the safety

factor, improve performance, and reduce costs in comparison with conventional construction

alternatives. In the case of embankments on extremely soft foundations, geosynthetics can permit

construction to take place at sites where conventional construction alternatives would be either

impossible or prohibitively expensive. (Chen W.F and Liew J.Y, 2003) Geosynthetics are

particularly useful in road pavement construction and the earthworks associated with road

construction. Geosynthetics used for construction projects are manufactured from synthetic

polymers such as polypropylene, polyesters, polyethylene, polyamide (nylon), poly-vinyl

chlorides (PVC), and fibreglass. Polypropylene and polyester are the most used. Compared to


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natural fibres, the polymeric geosynthetics offer long-term durability in the presence of elements

commonly encountered in construction (e.g. moisture and other types of corrosive chemicals)

In developing countries, the use of geosynthetics is relatively new but gaining widespread

popularity in construction. Geosynthetics are becoming rapidly popular in construction because

of their ability to perform certain necessary functions while offering practical advantages such

as:

i. A wide availability of products from the market placeii. The relative ease of shipping and field handling (flexibility)iii.

Rapid installation techniques, i.e fast speed of construction, without the need for

heavy equipment such as earth-moving machines.

iv. Lightweight in comparison with other construction materials, therefore imposingless stress upon the foundation

v. Durability and long life when properly selectedvi. General environment safety, since they will not degrade. (However, there is

possibility of degradation if exposed to sunlight and certain highly corrosive

chemicals) (Okunade, 2010)


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2.1 TYPES OF GEOSYNTHETICS

Geosynthetics are usually produced either in sheets or in fabric filaments (fibres) with the

major variations in their composition, thickness and strength. These are then further worked

upon in the production process to produce the construction geosynthetics group. The different

types of this geosynthetics group products are geotextiles (geofabrics), geogrids, geonets,

geomembranes, geosynthetic clay liners (GCL), geopipes or geotubes, geocells, geofoams,

drainage/infiltration cells and geocomposites.

Below is the description of the above listed materials:

1. Geotextile or Geofabrics:Geotextiles form one of the two largest groups of geosynthetic

materials. They are indeed textiles in the traditional sense, but consist of synthetic fibres (all are

polymer-based) rather than natural ones such as cotton, wool, jute ` Thus, biodegradation and

subsequent short lifetime is not a problem. These synthetic fibres are made into flexible, porous

fabrics by standard weaving machinery or they are matted together in a random nonwoven

manner. Some are also knitted. The major point is that geotextiles are porous to liquid flow

across their manufactured plane and also within their thickness, but to widely varying degree.

There are at least 100 specific application areas for geotextiles that have been developed;

however, the fabric always performs at least one of four discrete functions: separation,

reinforcement, filtration and/or drainage. According to ASTM, a GEOTEXTILE is any

permeable textile material used with foundation soil, rock, earth, or any other geotechnical

engineering-related material, as an integral part of a man-made project, structure or system.

(Wikipedia, 2011)


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2. Geogrids: they are unitized woven yarns or bonded straps. Geogrids consist of heavy

strands of plastic materials arranged as longitudinal and transverse elements to outline a

uniformly distributed and relatively large and gridlike array of apertures in the resulting sheet.

These apertures allow direct contact between soil particles on either side of the sheet. (Bergado

and Abuel-Naga, 2005)

According to Wikipedia, Geogrids represent a rapidly growing segment within

geosynthetics. Rather than being a woven, nonwoven or knitted textile fabric, geogrids are

polymers formed into a very open, gridlike configuration, i.e., they have large apertures between

individual ribs in the machine and cross machine directions. Geogrids are (a) either stretched in

one or two directions for improved physical properties, (b) made on weaving or knitting

machinery by standard textile manufacturing methods, or (c) by bonding rods or straps together.

There are many specific application areas, however, they function almost exclusively as

reinforcement materials. Modern geogrids were invented by Dr. Brian Mercer (Blackburn, UK)

in the late 1970s. Dr. Mercer devised and patented the stretched sheet method of production

which results in a stiff polymer grid and avoids the bonding of separate elements required in a

woven or knitted grid. Subsequent development by Dr. Mercer led to the uniaxial (single

direction stretch) geogrid with rectangular apertures and the biaxial (two way stretch) geogrid

with virtually square apertures.

3. Geonets: A geosynthetic material consisting of parallel sets of intersecting ribs that form

a three-dimensional net-like material. They are used to improve drainage by creating a thin

plane for water to travel through. (Kercher, 2011)


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4. Geomembranes: A geosynthetic material that is virtually waterproof when used as a

fluid barrier. A common application of this is a landfill liner.

5. Geocomposite: A material made up of a combination of geosynthetic materials that is used to

improve performance by combining the benefits of two types of geosynthetics.

There are virtually hundreds of different types of geosynthetic products available on the market

today. Please remember that all geosynthetic materials work in some type of application, but no

geosynthetic works in all applications. Therefore, make sure that you have the right geosynthetic

product for the right job.

2.2 WHY USE GEOSYNTHETICS?

One common question asked is, Why do geosynthetics need to be used to improve the

performance of the existing soils? In many cases, the existing soil has many inherent flaws

including:

1. Non-Uniform Consistency

Soils are made up of different types of particles such as gravel, sands, silt, clay and possibly

organic materials. Many times, the consistency of the soil (types of particles) can vary

throughout the length of the project. This can have a significant effect on such factors as

drainage, settlement, frost heaves, etc., all of which can create problems.


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2. Unstable Soils

In areas where soils consist of clays, silts and organics, especially in areas that drain poorly, the

subgrade may be unstable. As a result, the unstable soil is not able to provide adequately support

for a road or embankment.

3. Moisture Problems

Depending upon the consistency of the soil, the presence of moisture can create such problems as

loss of strength, swelling/shrinking, and frost heave.

4. Tensile Strength

Most soils can resist forces that compress the material (to a certain level). However, soils cannot

resist forces that pull the soil apart (tensile force).In situations where the existing soils exhibit

one or more of the above-mentioned problems, traditional alternatives include: remove and

replace poor soils, soil stabilization, use of piles or cassions, and/or installation of complex

drainage systems. These solutions can be very costly and time consuming. Another potential

solution is to use geosynthetics. Unlike soils, geosynthetics are manufactured specifically to

provide consistent properties that can be designed by the manufacturer and specified by the

user. Other benefits include ease of construction, increased life of the structure and reduced

maintenance requirements.

In many cases, the use of geosynthetics will allow for the utilization of lower quality fill

materials, less fill material, or reduce the amount of necessary excavation. In these cases,

geosynthetics can reduce the overall cost of the project. However, not all applications of

geosynthetics produce direct cost savings by lowering the initial cost of the project. In some


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situations, the cost savings result from an expected reduction in future maintenance costs and/or

an increase in the life of the project (based on a life cycle cost analysis).

Since geosynthetics can increase the life of a road and reduce the long-term maintenance

requirements, local agencies should consider amending their design and/or construction

ordinances to require the use of geosynthetics in new road construction and rehabilitation

projects, when feasible. Although this requirement will slightly increase the cost of the project, it

should provide long-term cost savings to the agency when it has to maintain the facility(road,

bridgeabutment, embankment, etc.).

2.3 GENERAL USES OF GEOSYNTHETICS

Four of the most common general uses of geosynthetics for local agencies are:

1. SeparationOne of the most common uses of geosynthetics is to use a geotextile to provide separation of

two layers with different soil properties. Separation is the placement of a flexible

geosynthetic material, like a porous geotextile, between dissimilar materials so that the

integrity and functioning of both the materials can remain undisturbed or even

improved. Using a road as an example, the separator will prevent the aggregate base course

from sinking into weaker subgrade material (aggregate loss) and preventing fine material in

the subgrade from pumping up into the aggregate base course (pumping). If aggregate loss

or pumping occurs, the strength of the pavement can be drastically reduced as shown in Plate

1 below which shows the reduced effective thicknessof the aggregate base course.


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a) Aggregate Loss due to lack of separation b) Separator prevents Aggregate

Loss

Plate 1 - Geosynthetic Separator preventing Aggregate Loss (Kercher et.al)

2. Filtration

In this type of application, the geosynthetic acts as a filter by preventing material from washing

out while allowing the water to flow through. The most common uses of this application are:

geotextiles which wrap around an edge drain (see Plate2), geotextiles placed under erosion

control devices, and geotextiles used behind structures such as retaining walls.

Plate 2 - Edge Drain wrapped with Geotextile (Kercher, et. al)


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3. Drainage

Although filtering applications are commonly referred to as drainage applications, they are

different. Drainage applications refer to situations where the water flows within the plane of the

geosynthetic product (in-plane drainage). In filtration applications, the water flows across the

plane of the material.

Although certain types of geotextiles provide some in-plane drainage, most drainage situations

require a geo-composite drainage product such as prefabricated sheet drains that provide a much

greater drainage capacity.

4. Reinforcement

In this application, the structural stability of the soil is greatly improved by the tensile strength of

the geosynthetic material. This concept is similar to that of reinforcing concrete with

steel. Since concrete is weak in tension, reinforcing steel is used to strengthen it. Geosynthetic

materials function in a similar manner as the reinforcing steel by providing tensile strength that

helps to hold the soil in place. Reinforcement provided by geotextiles or geogrids allows

embankments and roads to be built over very weak soils and allows for steeper embankments to

be built.

Plate 3 Soil Reinforcement of an Embankment using a Geosynthetic (Kercher et.al)


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Plate 4Earth Reinforced Retaining Wall using a Geosynthetic (Kercher et.al)

5. Barrier (Containment or Sealing)The barrier or containment function involves the use of an impervious geosynthetic for situations

where structures require a water-proofing membrane, or to function as a no-leak ground lining

for liquid and solid waste disposal sites and the top capping seal. This function is best performed

by a geomembrane. A non-woven geotextile performs this function when impregnated with

asphalt or other polymeric mixes rendering it relatively impermeable to both cross-plane and in-

plane flow. The classic application of geotextile as a liquid barrier is paved road rehabilitation.

Here, the nonwoven geotextile is placed on the existing pavement surface following the

application of an asphalt tack cloth. The geotextile absorbs asphalt to become a waterproofing

membrane minimizing vertical flow of water into the pavement structures. Other appropriate

geosynthetics are geosynthetic clay liners and certain geocomposites.

6. Protection

The protection function relates to including a protective geosynthetic for strength or

resistance to surrounding conditions as part of a geocomposite in a situation where the material

used to provide a major function, for example, drainage, is vulnerable to conditions present in the


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surrounding environment. Some geosynthetic and natural barriers need to be protected against

drainage.

7. Erosion control

The erosion control function is concerned with the geosynthetics to hold surfaces in place and

prevent erosion. Some geosynthetics permit protective vegetation to grow through the fabric so

that a natural (rooted) resistance to erosion develops. The geosynthetic may be designed to

gradually decompose or degrade.

2.4 PRIMARY FUNCTIONS SUITED TO THE GEOSYNTHETIC SUBGROUPS

The primary functions performed by geosynthetics are separation, filtration, drainage,

reinforcement, provision of a fluid barrier, and environmental protection and erosion control, as

detailed above. Geosynthetics are available in a wide range of forms and materials, each to suit a

slightly different end use. The function in view for each end use will determine the appropriate

type of geosynthetic to be employed. The primary functions most suited to the various

geosynthetic subgroups are as follows:

i. Geotextiles: The geotextiles have found widespread use in diverse areas of application.Geotextiles can generally be used for any function, as long as the proper synthetic and

composition are selected. The fabric always performs at least one of the five discrete functions of

separation, reinforcement, filtration, drainage and erosion control.

In separation, they can be used at the boundary between different soil materials to maintain a

separation (hinder the penetration of fine particles into coarse grained soil under load) but still


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permits the movement and passage of water. Also, the use of thick non-woven geotextiles for

cushioning and protection of geomembranes is in this category.

Geotextiles can be used as reinforcement of embankments, slopes, retaining structures against

failure. Geotextiles with high planer permeability (ability to conduct flow within the thickness of

the fabric) can be used for the drainage function by collecting and transporting of water in the

plain of the drainage layer. They can be used in foundation drains and under-drains etc.

For filtration, geotextiles are used to allow the passage of water and protect the soil structure

subjected to hydrodynamic forces. Geotextiles can be used in the protection of surface against

erosion.

ii. Geogrids: The geogrids function almost exclusively as a reinforcement material.However, they can also be used in some special cases of separation.

iii. Geonets: The geonets are exclusively used for the drainage function and for erosioncontrol.

iv. Geomembranes: These find application primarily within the containment or barrierfunction and within the drainage function. Geomembranes are usually impermeable or with low

permeability. They are therefore used for containment or barrier function as protective liners and

covers. They may be used as buried or exposed linings to prevent seepage or infiltration into

reservoir and impounding areas. Movement of water through an earth dike can be prevented by

installing a geomembrane lining on the dikes upstream side. Seepage beneath a dam can be

reduced by placing an impervious geomembrane to act as an upstream blanket. Geomembranes

are also used to prevent groundwater contamination below solid waste landfills.


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Geomembranes with high planer permeability (ability to conduct flow within the thickness of the

fabric) can be used for the drainage function.

v. Geosynthetic Clay Liners (GCL): Being rolls of thinly layered bentonite claysandwiched between two geotextiles or bonded to a geomembrane, these products are used as a

composite component beneath a geomembrane or by themselves as primary or secondary liners

(to fulfil the containment or barrier function).

vi. Geopipes: This function is clearly drainage. Buried plastic pipes (geopipes) are beingused in all aspects of geotechnical, transportation and environmental engineering. They are all

the more important because of the critical nature of leachate collection pipes coupled with high

compressive loads.

vii. Geofoams: Geofoams are mainly used as lightweight fill on soft ground. It caneffectively relieve lateral pressure on walls. This application area can be classed under the

separation function.

viii. Geocells: Also known as cellular confinement systems, these find application in thereinforcement function. They are traditionally used in slope protection and earth retention

applications, while geocells made from advanced polymers are being increasingly adopted for

long-term load support.

ix. Drainage/Infiltration Cells: These find application also within the reinforcementfunction. Implementation and application can range from roof garden, hydrostatic pressure relief

for retaining walls, increased catchment area and efficiency for storm water harvesting, among

others.

x. Geocomposites: The geocomposites, being a combination form an exciting area whichbrings out the best creative efforts of the engineer. The application areas are numerous and


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growing steadily and they encompass the entire range of functions for geosynthetics: separation,

reinforcement, filtration, drainage and liquid barrier.

Summarizing all the above functionalities of the above explained subgroups of

geosynthetic materials in Table 1 we have:

Table 2.4Identification of the Usual Primary Function for Each Type of Geosynthetic

(Wikipedia, 2011)

Type of Geosynthetic (GS) Separation Reinforcement Filtration Drainage Containment

Geotextile (GT) X X X X

Geogrid (GG) X

Geonet (GN) X

Geomembrane (GM) X

Geosynthetic Clay Liner

(GCL)

X

Geopipe (GP) X

Geofoam (GF) X

Geocells (GL) X X

Drainage cell (DC) X X X

Geocomposite (GC) X X X X X


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2.5 APPLICATIONS OF THE GEOSYNTHETIC SUBGROUPS IN

INFRASTRUCTURE DEVELOPMENT

The functions of the geosynthetics subgroups, in conjunction with the advantages they offer,

have made them suitable for a wide range of applications and have caused them to be vastly used

in many, if not all, areas of infrastructure development. The products have been and are currently

being used in many civil, geotechnical, transportation, geoenvironmental, hydraulic and private

development applications including roads, airfields, railroads, embankments, retaining structures,

reservoirs, canals, dams, erosion control, sediment control, landfill liners, landfill covers, mining,

aquaculture and agriculture. (Wikipedia, 2011)

Within each of the areas mentioned above, geosynthetics have found multiple applications. For

example, geosynthetics have been and continue to be used in all facets of the transportation

industry, including roadways, airports, railroads and waterways. It is expected that in the near

future geosynthetics will be the first choice for all drainage, filtration, and separation designs

(except where soil mass is required to aid stability or to provide volume for other necessary

functions such as aerobic and anaerobic decompositions).

It will be almost impossible to mention all the areas of application of geosynthetics in

infrastructure development, since these are areas run into hundreds in number (Wikipedia 2011).

However, a few of these areas of application of geosynthetics in infrastructure development will

be mentioned here (Meccai and Hassan, 2004; Joint Departments of U.S Army and Airforce,

1995; Guyer, 2009; Geosynthetics Materials Association, 2010; Wikipedia, 2011).


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2.5.1 Geosynthetics in Transportation Engineering

Geofoam has found application in transportation as super lightweight fill, with its density of 24

to 48 kilograms per cubic meter (kg/m3), compared to densities of other lightweight materials

ranging from 800 to 1120 kg.m3. Geofoams lightweight makes it viable option for landslide

repair, and for embankments on soft, compressible deposits. Geofoam is also used for thermal

insulation of pavements and foundations. Geogrids have been used for soil reinforcements in

embankments and walls, subgrade stabilization, and embankment base reinforcement. Geogrids

are characterized by integrally connected elements with in-plane apertures (openings) uniformly

distributed between the elements. The apertures allow the soil to fill the space between the

elements, thereby increasing soil interaction with the geogrid and ensuring unrestricted vertical

drainage. All these applications are not only in highway, but also in railroad track construction

and rehabilitation.

2.5.2 Geosynthetics in Pavement Structures

Applications of geosynthetics within pavement structures have been primarily in the areas listed

below:

a) Pavement surface layer reinforcement (asphalt concrete overlays of existing asphaltconcrete and Portland cement concrete surfaces)

b)

Rehabilitation of pavement surfaces, reflective crack treatments, spot repairs, etc

c) Geotechnical reinforcement of unbound (flexible) bases, soft subgrade, embankmentson soft foundations etc.

d) Encapsulation and separation of materials


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e) Drainage applications, water control, granular drain performance (filters), pipingresistance, clogging prevention etc,

f) Moisture control.

2.5.3 Geosynthetics in Drains

Geomembranes (suitable for the barrier function) have been successfully used as the

waterproofing element in embankment dams (Cazzuffi, 1987), to rehabilitate old concrete and

masonry dams in order to reduce leakage phenomena that typically appear on these structures

after 30 to 40 years of operation, depending on the accuracy of construction and on conditions of

the damsite (Cazzuffi, 2000). Geosynthetics have also been used as chimney drains, filters

between fine-grained cores and shells of earthfill and rockfiil dams, as drains, as filters between

the foundation of the dam for stability, as protection for the upstream slope facings of the dams,

and as erosion control features on the downstream slope facings

2.5.4 Geosynthetics in Coastal defence installations

Geosynthetics have also found application in coastal defence installations. According to the

Industrial Fabrics Association (2009), geosynthetic technologies have emerged as a major tool in

the battle against shoreline erosion. The Geotube system involves filling a very large tubular

textile containers with local sand and sludge to hold unstable banks in place. Shoreline

stabilization frequently is accomplished with membranes covered by concrete or stone geotube

eliminate the need to transport those materials. In addition, over time the water will gradually

wash away the geotube contents, returning the shoreline to its original ecosystem. This has been

applied in Nigeria. In Nigeria, the Niger Rivers bank and delta are eroding, crumblinghouses


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and whole villages into the water. The Niger Delta Development Commission plans to install

scour aprons on the riverbed to prevent it being worn away, use geotubes to hold the aprons in

place.

2.5.5 Geosynthetics in Earth Retention and Slope Stability

Geosynthetics (geocells) have been employed to protect slopes against erosion, stabilize steep

slope surfaces, provide protective linings for channels, support heavy construction traffic on the

weak subgrade soils, and provide multi-layered earth-retaining structures. Geocells are typically

constructed of high-density polyethylene. The cells in the three-dimensional panels are opened

and filled with granular material, which adds weight to make the multi-layer system act as a

gravity retaining wall. Geogrids are also mainly used for reinforcement applications such as

reinforced vertical walls and steep slopes as well as reinforced foundations. Geotextiles can

improve soil strength at a lower cost than conventional soil nailing. In addition, geotextiles allow

planting on steep slopes, further securing the slope.

2.5.6 Geosynthetics in Landfills

Geomembranes serve as hydraulic barriers and have been used in conjunction with geonets in

landfill applications. They have also been used for containment of spills, leaking underground

storage tanks, or hazardous materials. Safe venting of toxic gases is also made possible through

geosynthetics (geonets) with in-plane porosity. Geopipes are used fordrainage of liquids or

gas(including leachate or gas collection in landfill applications). In some cases, the perforated

pipe is wrapped with a geotextile filter.


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2.5.7 Geosynthetics in Water and Liquid Containment Applications

Geomembranes, as well as geosynthetic clay liners (when hydrated), are relatively impermeable

and are used as liners for fluid or gas containment and as vapour barriers. They are used in the

area of potable wastewater treatment, golf and decorative ponds, aquaculture ponds, floating

covers, etc.

2.5.8 Geosynthetics in Drainage Systems

Geocomposites are designed to replace aggregate and or perforated pipe subsurface drainage

systems. A geocomposite consists of a deformed, perforated, or slotted plastic core and a

geotextile (filter) fabric wrap. Geocomposites include geonets, pavement edge drains (drain

mats), and sheet (wall) drains. Wick drains used to expedite drainage of deep, compressible soil

deposits, have also been included in the geocomposite category.

2.5.9 Geosynthetics in Erosion and Sediment Control

Geosynthetics (perforated geopipes) have been placed in drainage channels to collect storm

water, while geonets have been used to line these same channels to permit the growth of

vegetation through them whereby the erosion of the drainage channel is curtailed. Geosynthetics

have also been used for sediment control.


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2.6 EFFECTIVENESS IN REDUCING THE COST OF INFRASTRUCTURE

Geosynthetics can be a better and cost effective alternative to other materials in

infrastructure development but continue to be underutilized, perhaps due to ignorance of

unfamiliarity of civil engineering practitioners with them. The following points merely give

illustrations of how the usage of geosynthetics can contribute immensely to the reduction of

infrastructure if adequately utilized in the vast areas of application across the spectrum of

national development.

The use of geosynthetics permit the usage of local soil materials (though weak), ratherthan imported quarry product (which would be costlier), in the place of construction.

Their advantage of rapid installation techniques lead to reduced periods of constructionand therefore, reduced construction costs.

The light weight of geosynthetics, in comparison with other construction materials,makes them impose less stress upon the foundation, and therefore, less damage over time.

Their durability and long-life preclude shorter design life spans of projects and the needfor rehabilitation and major maintenance operations.

Geosynthetics are generally very cheap and more cost effective than other materials (forexample, when used to fulfil the reinforcement function).

Geosynthetics provide easy and cost effective way out of difficult situations being usablewhen other materials are unusable. For example, geogrids may be used as a substitute in

lieu of lime in sulphate laden soils where lime is detrimental or urban areas where lime

may not be tolerated or combinations of these and soft soils.


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Geotextiles extend the service life of roads. Increase their load carrying capacity, andreduce rutting (Meccai and Al-Hasan, 2004). These are achieved through the stabilization

and separation functions. When used in pavement applications, geosynthetics help to

restrain base material during compaction or loading; they also serve as a separation layer

to prevent excess migration and intermingling of pavement layers at interfaces. In

pavement overlays, geotextiles provide the added advantages of resisting moisture

intrusion into lower pavement layers, thereby maintaining high material strengths,

retarding reflective cracking in the overlay from existing layers of hot-mix asphalt

concrete or from cracks and joints in rigid pavement by acting as a stress absorbing

membrane interlayer, and increasing the structural stability by providing for more stable

subgrade moisture contents.

When used to fulfil the filtration process in roads, geotextiles have significant advantages(Meccai and Hasan, 2004). The removal of water is important to the success of many

civil engineering problems. In transportation applications, if the base course does not

drain rapidly enough, stress form the traffic loading is transferred to the subgrade with

little or no reduction, resulting in accelerated road failure. The removal of water must be

performed in a controlled fashion. Otherwise, severe erosion, piping, settlement of soils

may result in undermining adjacent structures. To accomplish this task, the drainage

system should fulfil two criteria: maintenance if the permeability (by providing relatively

unimpeded flow of water), and filtration of the base soil (by preventing the migration of

the soil fines into the drain). These criteria can be met by using several layers of specially

graded aggregates. This often proves to be an extremely expensive requirement to meet.

The same result can be achieved at a fraction of the cost by using selected geotextiles,


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which act as filters around the aggregate drainage system. The introduction of geotextile

lined drained systems has enhanced the technical properties and economic application of

blanket and trench drains under and adjacent to pavement structures. The excellent

filtration and separation characteristics associated with geotextiles permit the use of a

single layer of open graded aggregate base or trench aggregate enveloped in a geotextile.

Thus, when geosynthetics are used within pavement structures for drainage and moisture

control, they enhance the pavement structure and lengthen its performance by reducing

the influence moisture has on the pavement materials.

When used for soil walls, some advantages of geotextile-reinforced walls overconventional concrete walls are the following:

(a) They are economical.

(b) Construction usually is easy and rapid. It does not require skilled labour or

specialized equipment. Many of the components are prefabricated allowing

relatively quick construction.

(c) Regardless of the height or length of the wall, support of the structure is not

required during construction as for conventional retaining walls.

(d) They are relatively flexible and can tolerate large lateral deformations and

large differential vertical settlements. The flexibility of geotextile-reinforced walls

allows the use of a lower factor of safety for bearing capacity design than for

conventional more rigid structures (Joint Departments of the U.S Army and Air

Force, 1995).


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When geosynthetics are used to form embankments under roads, the near-vertical sideslopes obtained greatly reduce the width of the embankmentsbase, thereby reducing the

extent of the road right-of-way and the consequent land acquisition costs. Moreover,

erosion of the slope surfaces is prevented, resulting in more stable pavement structures

and less maintenance costs.


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CHAPTER THREE

RESEARCH METHODOLOGY

3.0 INTRODUCTION

The designed methodology is based on previous years of research and experience in geotextile

filtration design. The approach presents a logical progression through four steps.

Step 1: Defining the Application Filter Requirements

Step 2: Defining Boundary Conditions

Step 3: Determining the Soil Retention Requirements

Geotextile filters are used between the soil and drainage or armoring medium. Typical drainage

media include natural materials such as gravel and sand, as well as geosynthetic materials such

as geonets and cuspated drainage cores. Armoring material is often riprap or concrete blocks.

Often, an armoring system includes a sand bedding layer beneath the surface armor. The

armoring system can be considered to act as a drain for water seeping from the protected slope.

3.1 SAMPLE COLLECTION

The materials that were used for this investigation are clayey, organic and lateritic soils. For the

laboratory tests, three soil samples were collected. Organic soil and clayey soil were gotten from

Apatapiti layout, Akure and Laterite gotten from Akure-Lagos Expressway opposite FUTA

North Gate. The materials were gotten in polythene to prevent loss of moisture to the

atmosphere. Analysis was carried out in order to ascertain the physical and engineering

properties of the samples.


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3.2 LABORATORY TEST

Tests implemented or performed on natural clayey, organic and lateritic soils collected for this

project include particle size distribution, grain size analysis, moisture content, Atterberg limits

and California Bearing ratio tests (CBR) in order to assess their geotechnical properties

3.2.1 Soil Particle-Size Distribution

The natural soil samples were crushed respectively and 500grams of each sample was measured.

The sieves were arranged in decreasing order of hole size and the soil samples retained on each

sieve was weighed to determine the individual weight.

Thereafter, the soil was placed in an array of sieves in the manual shaker and shaken for

15minutes. The sieves were then weighed independently along with the soil retained. The

percentage retained in each sieve was determined after which the distribution curves were

plotted.

The particle-size distribution of the soil to be protected should be determined using test method

ASTM D 422. The grain size distribution curve is used to determine parameters necessary for the

selection of numerical retention criteria.

3.2.2 Soil Atterberg LimitsThe test was carried out on natural soil samples in order to classify into standard groups and

these limits include: liquid, plastic and shrinkage limits. Some useful information obtained from

knowledge of these limits are:

1. It enables to identify and classify the soil.


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2. Shear strength of soil can be inferred from these properties.3. Results of the liquid limit can be useful in assessment of the settlement of soil.For fine-grained soils, the plasticity index (PI) should be determined using the Atterberg

Limits test procedure BS 1377-2.

(i) Liquid limitThe liquid limit of a soil is defined as the moisture content of which the soil passes from

plastic to liquid state as determined in accordance with the standard procedure, BS 1371,

London, 1961.

This procedure consists of a portion of air-dried soil, which was pulverized in order to make

it pass through sieve 425um. 250grams of the soil passing was mixed with water to form a

thick, homogenous paste. The paste was placed in a casagrande cup and levelled parallel to

the base of the cup. The paste was divided into two halves using the grooving tool and blows

were given to the paste till it closed in. small samples of the paste were collected into

containers and oven-dried for 24hrs. Other pastes were collected by varying the moisture

content of the paste for the three samples.

The relationship between moisture content and the number of blows were plotted and the best

straight line between these points was drawn. The moisture content corresponding to

25blows on the graph was taken as the liquid limit.


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(ii) Plastic limitThe plastic limit of a soil is defined as the moisture content at which the soil becomes too dry

to be in the plastic condition or the minimum water content at which a soil can be rolled into

threads of 3mm diameter between the palm of the hand. The soil thread at plastic limit

crumbles under the rolling action. At this stage, moisture was added again and the average

value of the moisture content was taken as the plastic limit of the soil.

The numerical value between the liquid and the plastic limits of the soil is known as the

plasticity index. This is a measure of how much water a soil can absorb before dissolving

into a solution. The higher the value, the more plastic and weak the material is. Plastic soil

containing clay has PI of 10 to 50 or more.

(iii) Shrinkage limitShrinkage due to drying is significant in clays, but less in silt and sands. These tests enable

the shrinkage limit of clay to be determined i.e the moisture content below which clay ceases

to shrink. They also quantify the amount of shrinkage likely to be experienced by soils in

terms of the shrinkage ratio, volumetric shrinkage and linear shrinkage.

3.2.3 Specific gravity

Natural soils for the three samples were collected and oven-dried and the natural moisture was

determined. Three specific gravity bottles were weighed empty and the bottles were filled with

water and reweighed. 50grams of the soil samples to be used were also weighed and poured


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inside the bottles. Distilled water was poured inside the three specimens. The particles inside the

water was stirred and left to settle for about 15minutes to get rid of the air bubbles. On settling,

more water was added to the brim of the bottle and it was covered with the lid. The outer part of

the bottles were dried and weighed. The sample was reweighed after 24hours and the values of

their respective specific gravities were determined.

3.2.4 Proctor compaction test

In the standard proctor test, 3000g of the sample was oven-dried. Proctor mould was set and

clamped. The soil was poured in a tray and 8% of water was added to it. It was properly mixed

with the hand and placed in the mould in three layers with 25 blows given to each layer with a

2.5kg rammer. The extension collar of the mould was removed and the excess specimen in the

mould was levelled with the edge of the mould and the specimen was weighed.

The specimen was removed from the mould and part of it was removed from the top and bottom

with the spatula and the moisture content was determined. 10%, 12%, 14% of water was

subsequently added to the sample and equally compacted and weighed. The amount of water

added increased arithmetically till there was a reduction in the weight of the mould and the

sample.

3.2.5 Determination of the Maximum Allowable Geotextile Opening SizeThe last step in determining soil retention requirements is evaluating the maximum allowable

opening size (O95) of the geotextile which will provide adequate soil retention. The O95 is also

known as the geotextiles Apparent OpeningSize (AOS) and is determined from test procedure

ASTM D 4751. AOS can often be obtained from manufacturers literature.


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3.2.6 Determination of the Moisture Content of the SoilTest procedure used was BS 812-109 1990 Part 109: Methods for determination of moisture

content. About 15g of the in-situ soil was placed in a can and weighed. It was then placed in an

oven to remove the moisture. The cans were re-weighed after 24hours and the moisture content

was determined.

3.2.7 California Bearing Ratio (CBR)Test procedure was according to BS 1377-4: Soils for civil engineering purposes: Part 4:

Compaction related tests. Includes:- the California bearing ratio, and the various methods of

determining the dry density, moisture content relationship of soil. 3kg of oven-dried sample was

thoroughly mixed with an appropriate amount of water and placed in a mould. The extension

collar and base plate was fixed. The soil in the mould was compacted in 3 equal layers, each

layer compacted with 25blows of the 2.5kg rammer. The collar was removed and the soil was

trimmed off. The base plate and displacer disc was removed and the mould was weighed with the

compacted soil.

The penetration piston was placed at the centre of the specimen with the smallest possible load

so that full contact between the piston and the sample was established. The strain and stress dial

gauge was set to zero and load was applied on the piston and records were taken after every

30secs. The maximum load corresponding to the penetration was determined when there was no

increase in the value of the dial reading. The mould was detached and about 15g was taken from

the top to determine the moisture content.


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3.3 PAVEMENT MODELING

In modeling for the pavement, four (4) wooden moulds were constructed, three to contain

the different soil layers and the geosynthetic material and the last one without geotextile. The

mould had dimensions length = 40cm, breadth = 20cm and height = 50cm to accommodate for

the height of the three sections of the pavement which are the base-course, sub-base and sub-

grade all 150mm in height with a camber of 4 percent for drainage.

In compaction of the sub-grades, the moulds were marked with the respective dimensions

and consideration was given to the camber and with the aid of a rammer, it was compacted with

several blows. The compacted soils were left to consolidate for a week and then the geotextile

was laid on the surface on the sub-grade.

The sandcrete which is the sub-base had a mix ratio of 3:1. 3 head-pans of stone dust to 1 head-

pan of cement was thoroughly mixed without the presence of water and placed in the mould and

compacted then sprinkled with water for 7 days to cure and to attain maximum strength.

Finally, the granite chippings used for the base course was placed and compacted also with the

ramming rod with the camber still maintained.

The side of the mould with the lower slope was removed. The moisture content of the sub-grade

was determined to check the effectiveness of the geotextile placed between the soil layers.


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40CM

20CM

50CM

15CM

SUB-BASE

15CM

SUBGRADE

15CM

BASE COURS

GEOTEXTILE

Plate 5Mould showing dimensions of the various cross sections


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CHAPTER FOUR

RESULTS AND DISCUSSION

For the purpose of identification, classification and determination of engineering characteristics

of the materials used, the laboratory tests were performed on the three samples collected. After

which the samples were used as test sub-grades in the pavement model.

4.0 PARTICLE-SIZE DISTRIBUTION

This test was performed on the natural soils and the results are shown in the appendix. They

were used for the classification of the samples.

Figure 1: Particle size distribution graph for Sample A


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Figure 2: Particle Size distribution graph for Sample B

Figure 3: Particle Size distribution for Sample C

According to the AASHTO classification, Sample A as shown above ranges between fine sand

and fine gravel, it is therefore an A-2-7 soil (Silty or clayey gravel sand), while Sample B ranges


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between the sand and gravel sizes. The material is gravelly sand with 1.84% clay fractions, it is

classified as A-2-4. Sample C which ranges from clay to fine sands is A-6 soil (Clayey soil)

4.1 ATTERBERG LIMIT TEST

The Atterberg Limit test was performed on the soil samples. The result for each soil samples are

shown in appendix II. The results show that Sample A has a liquid limit 35.5%, plastic limit

17.9% and plasticity index 17.6%, Sample B has a liquid limit of 38.7%, and plastic limit of

23.4% with plasticity index 15.3% and Sample C has a liquid limit 60.22%, plastic limit 25.9%

and plasticity index 34.32%. The graphs of the liquid limit for the respective soil samples are

plotted in appendix II.

When liquid limit falls between this category below:

L.L < 35 = (L) Low Plasticity

L.L = (35-40) = (I) Intermediate Plasticity

L.L = (50-70) = (H) High Plasticity

This implies that Sample A has intermediate plasticity, Sample B has low plasticity and Sample

C has high plasticity.

4.2 SPECIFIC GRAVITY TEST

The specific gravity of a soil is the ratio of a certain volume of the material the weight of an

equal volume of water. This is not suitable for soil containing more than 10% stones retained in

the 37.5mm BS test sieve and such should be broken down to less than this size.


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The result of the specific gravity test performed on the three samples A, B and C were found to

be 2.82, 1.79 and 2.56 respectively.

Table 4.2: Showing SG values of the soil samples

Soil Samples Sample A Sample B Sample C

Weight of empty glass + Lid W1 (g) 267.1 267.1 267.1

Weight of empty glass + Lid+ water

(g)W4

591.8 591.8 591.8

Weight of empty glass + Lid+ 50g

Soil sample (g) W2

317.1 317.1 317.1

Weight of empty glass + Lid+ water

+ 50g Soil sample (after 24hrs) (g)

W3

624.06 613.9 622.27

Specific Gravity

(W2-W1)

(W2-W1) - (W3-W4)

2.82 1.79 2.56

4.3 MOISTURE CONTENT

Table 4.3: Showing natural moisture content of soil samples

Samples Sample ASample B Sample C

M1= mass of empty clean

can (g)29.7

30 29.3

M2= mass of can and moist

soil (g)95.1

94.3 90.1


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M3= mass of can and dry soil

(g)74.3

82.7 75.02

W = moisture content 0.280.22 0.201

W0= aggregate moisture

content (%) 28 22 20.1

4.4 COMPACTION TEST

This test was performed on the natural soil samples to specify suitable moisture content for field

compaction. The laboratory results are shown in appendix III with the graphs showing the

relationship between dry density and moisture content for the soil samples. Sample A has a

maximum dry density (MDD) of 1680mg/m3and optimum moisture content (OMC) of 23%,

Sample B has MDD of 1525 mg/m3and OMC of 32.7% and Sample C has MDD 1452 mg/m

3

and OMC of 31.3%.

4.5 CALIFORNIA BEARING RATIO

This test was performed on the samples to readily know the true behaviour of the soil and the soil

resistance to shear. The results are shown in appendix III with graphs showing the relationship

between the dry densities and moisture content.

SAMPLES

2.5 mm CBR Penetration Values 5.0 mm CBR Penetration Values

TOP BOTTOM TOP BOTTOM

SAMPLE A 7.6% 4.2% 8.5% 4.6%

SAMPLE B 6.04% 4.5% 6% 5.26%

SAMPLE C 13.62% 15.095% 15.12% 16.29%


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The low CBR values exhibited by the samples A & B indicates that the sub-grade had a weak

bearing strength and is susceptible to erosion on exposure to precipitation or surface runoff,

thereby encouraging and exacerbating rutting and deformation of pavement.

4.6 PAVEMENT MODEL TEST

After allowing the model to properly compact, each model was tested by leaving them in the

open and letting normal weather conditions such as sunshine and rainfall act on them and then

the moisture content of the sub-grade were taken. Below are the average moisture content for

samples.

4.6.1 DRAINAGE TEST: this test was performed by taking the moisture content of the

varying sample sub-grades. It was observed that the soil without the geotextile had the higher

moisture content after exposure to natural weather conditions

Plate 6Side view of the pavement models, the 1st on the left without geotextile and the rest with

geotextile incorporated


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Table 4.6: Showing the moisture content of the soil sample used as sub-grades with and

without geotextile.

4.6.2 SEPARATION TEST: this test to shows that the geotextile material ensures proper

separation of layers in the road section as shown in the plates below.

Plate 7Proper Separation of sub-grade from the sub-base

SamplesWeight

of can

Weight of can +

wet sample(g)

Weight of can+ dry

sample(g)

Weightof wet

sample(g)

Weight of

dry soil(g)

Wt of

moisture(g)

Moiscont

%Sample A +

Geotextile layer29.3 56.2 50.7 24.9 21.4 3.5 25

Sample B +

Geotextile29.7 68.7 62.1 39 32.4 6.6 20

Sample C +

Geotextile29.4 46.7 44 17.3 14.6 2.7 18

Sample A without

Geotextile30 47.5 43.4 17.5 13.4 4.1 30


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Plate 7 shows a proper separation between the subgrade and the sub-base. This helps to prevent

the poor subgrade from pumping up into the aggregate base course and it also prevents the

aggregate base course from sinking into or mixing with the weaker subgrade material. Plate 8 on

the other hand shows an improper separation between the subgrade and the sub-base. From the

plate, it is evident that the sub-base has sunk into the subgrade.

Plate 8Merging - Improper Separation of sub-grade from the sub-base


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CHAPTER FIVE

CONCLUSION AND RECOMMENDATION

5.0 CONCLUSION

From the above analysis taken on both soil sample and material it is of economic benefit to

introduce the use of geotextiles in road construction as it reduces the act of borrowing to fill

when the in-situ soil can easily be enhanced by use of geosynthetics.

Geotextiles are effective tools in the hands of the civil engineer that have proved to solve a

myriad of geotechnical problems. With the availability of variety of products with differing

characteristics, the design engineer needs to be aware of not only the application possibilities but

also more specifically the reason why he is using the geotextile and the governing geotextile

functional properties to satisfy these functions. Design and selection of geotextiles based on

sound engineering principles will serve the long-term interest of both the user and the industry.

5.2RECOMMENDATIONSThis project has been able to show the beneficial functions of geotextiles in road construction as

sampled on the various soil types. From results gotten it is quite economical to introduce the use

of geosynthetics as a whole into the Engineering industry. The material should be used also in

effective separation of subgrade and sub-base courses in road construction and other engineering

constructions.


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Methods on the Quality Assurance of Landfill Liner

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ASTMD5101-90, Standard test method for measuring the soil-textile system

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for Testing and Materials, Philadelphia, PA, USA.

Bergado, D.T., & Abuel-Naga, H.M (2005), Tsunami devastations and reconstruction with

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