CONSTRUCTION

METHODS &

TECHNOLOGY

CIVL462CIVL462

Lecture No: 2

� Earthmoving is the process of moving soilor rock from one location to another andprocessing it so that it meets constructionrequirements of location, elevation,density, moisture content, and so on.

The Earthmoving Process

� Activities involved in this process includeexcavating, loading, hauling, placing(dumping and spreading) compacting,grading, and finishing.

The choice of equipment to be used on a constructionproject has a major influence on the efficiency andprofitability of the construction operation.Although there are a number of factors that should beconsideredin selectingequipmentfor a project,(1) the

Equipment Selection

consideredin selectingequipmentfor a project,(1) themost important criterion is the ability of theequipment to perform the required work. Amongthose items of equipment capable of performing thejob, the principal criterion for selection should bemaximizing the profit or return on the investmentproduced by the equipment

Other factors that should be considered when selectingequipment for a project include (2)possible future useof the equipment, (3) its availability, (4)the availabilityof parts and service, and (5) the effect of equipmentdowntime on other construction equipment and

Equipment Selection

downtime on other construction equipment andoperations

Excavator

Bulldozer

Scraper

Roller

Dump truck

Soil ConditionsThere are three principal conditions or states in which earthmovingmaterial may exist:bank, loose, and compacted. The meanings ofthese terms are as follows:

• Bank: Material in its natural state before disturbance. Oftenreferredto as“in -place” or “in situ.” A unit volume is identified as

SOIL VOLUME-CHANGE CHARACTERISTICS

referredto as“in -place” or “in situ.” A unit volume is identified asa bank cubic yard (BCY) or a bank cubic meter (BCM).

• Loose: Material that has been excavated or loaded. A unit volumeis identified as a loose cubic yard (LCY) or loose cubic meter(LCM).

• Compacted: Material after compaction. A unit volume is identifiedas a compacted cubic yard (CCY) or compacted cubic meter (CCM

A soil increases in volume when it is excavatedbecause the soil grains are loosened during excavationand air fills the void spaces created. As a result, a unitvolume of soil in the bank condition will occupy morethan one unit volume after excavation.Thisphenomenonis calledswell.

Swell

phenomenonis calledswell.

Swell may be calculated as follows:

EXAMPLE

Find the swell of a soil that weighs (1661 kg/m3) in its natural state and (1186 kg/m3) after excavation.

Swell

SOLUTION

That is, 1 bank cubic (meter) of material willexpand to 1.4 loose cubic (meters) after excavation.

Swell

When a soil is compacted, some of the air is forced outof the soil’s void spaces. As a result, the soil willoccupy less volume than it did under either the bank orloose conditions.

Shrinkage

This phenomenon, which is the reverse of the swellphenomenon, is calledshrinkage.The value of shrinkage may be determined as follows:

EXAMPLE

Find the shrinkage of a soil that weighs (1661 kg/m3) in its natural state and (2077 kg/m3) after compaction.

Shrinkage

SOLUTION

Hence 1 bank cubic (meter) of material will shrinkto 0.8 compacted cubic (meter) as a result ofcompaction.

�In performing earthmoving calculations, it is importantto convert all material volumes to a common unit ofmeasure. Although the bank cubic (meter) is mostcommonly used for this purpose, any of the three volumeunits may be used.�A pay (meter)is the volume unit specifiedas the basis

Load and Shrinkage Factors

�A pay (meter)is the volume unit specifiedas the basisfor payment in an earthmoving contract. It may be any ofthe three volume units.�Because spoil bank volume are commonly expressed inloose measure, it is convenient to have a conversion factorto simplify the conversion of loose volume to bankvolume.

Load and Shrinkage Factors

• The factor used for this purpose is called aload factor. A soil’s load factor may becalculated by using the following equation:

• Loose volume is multiplied by the load factorto obtain bank volume.

Load and Shrinkage Factors

• A factor used for the conversion of bankvolume to compacted volume is sometimesreferred to as ashrinkage factor.

Load and Shrinkage FactorsEXAMPLE

A soil weighs (1163 kg/LCM), (1661 kg/BCM), and(2077 kg/CCM).(a) Find theloadfactorandshrinkagefactorfor thesoil.(a) Find theloadfactorandshrinkagefactorfor thesoil.(b) How many bank cubic meters (BCM) andcompacted cubic meters (CCM) are contained in 593300 loose cubic meters (LCM) of this soil?

Load and Shrinkage Factors

SOLUTION

ESTIMATING EARTHWORK VOLUME

When planning or estimating an earthmoving project it isoften necessary to estimate the volume of material to beexcavated or placed as fill. The procedures to befollowed can be divided into three principal categories:(1) pit excavations(small, relatively deepexcavations(1) pit excavations(small, relatively deepexcavationssuch as those required for basements andfoundations), (2) trench excavation for utility lines,and (3) excavating or grading relatively large areas.

Procedures suggested for each of these three cases aredescribed in the following sections

ESTIMATING EARTHWORK VOLUME

Pit ExcavationsFor these cases simply multiply the horizontal

area of excavation by the average depth ofexcavationexcavation

Volume = Horizontal area × Average depth

ESTIMATING EARTHWORK VOLUME

EXAMPLEEstimate the volume of excavation required (bankmeasure) for the basement shown in Figure. Valuesshown at each corner are depths of excavation. Allvaluesarein (m). 9.15 mvaluesarein (m).

1.8 m 2.5 m

1.8 m 2.3 m

9.15 m

7.63 m

ESTIMATING EARTHWORK VOLUME

Trench ExcavationsThe volume of excavation required for a trench

can be calculated as the product of the trenchcross-sectional area and the linear distancecross-sectional area and the linear distancealong the trench line

Volume = Cross-sectional area × Length

ESTIMATING EARTHWORK VOLUME

EXAMPLEFind the volume (bank measure) of excavation requiredfor a trench (0.92 m) wide, (1.83 m) deep, and (152 m)long. Assume that the trench sides will beapproximatelyvertical.approximatelyvertical.

ESTIMATING EARTHWORK VOLUME

Large AreasTo estimate the earthwork volume involved in large or

complex areas, one method is to divide the area into a gridindicating the depth of excavation or fill at each gridintersection.intersection.

Assign the depth at each corner or segment intersection aweight according to its location (number of segment linesintersecting at the point). Thus, interior points(intersection of four segments) are assigned a weight offour, exterior points at the intersection of two segments areassigned a weight of two, and corner points are assigned aweight of one.

Average depth is then computed using equation and multiplied by thehorizontal area to obtain the volume of excavation. Note, however,that this calculation yields the net volume of excavation for the area.

ESTIMATING EARTHWORK VOLUME

ESTIMATING EARTHWORK VOLUME

Example:

Find the volumeof excavationrequiredfor the areaFind the volumeof excavationrequiredfor the areashown in Figure. The figure at each grid intersectionrepresents the depth of cut at that location. Depths inparentheses represent meters.

Example: Large Areas

1.31 1.31

Volume = 11142 × 1.31 = 14596.02 BCM

Solve this Example

A mass diagramis a continuous curve representing the accumulatedvolume of earthworkplotted againstthe linear profile of a roadwayor

ESTIMATING EARTHWORK VOLUME

Construction Use of the Mass Diagram

volume of earthworkplotted againstthe linear profile of a roadwayorairfield.

Mass diagrams are prepared by highway and airfield designers to assistin selecting an alignment which minimizes the earth work required toconstruct the facility while meeting established limits of roadway gradeand curvature.

Fig: Mass Diagram

ESTIMATING EARTHWORK VOLUME

Some of the information which a mass diagram can provide a construction manager includes

Construction Use of the Mass Diagram

construction manager includesthe following.• The length and direction of haul within a balanced section.• The average length of haul for a balanced section.• The location and amount of borrow (material hauled in from a borrow pit) and waste (material hauled away to a waste area) for the project..

Keys to Successful Earthwork Operations

1. Control surface and subsurface water

2. maintain optimum moisture range by drying, mixing , or wetting

ESTIMATING EARTHWORK VOLUME

3. identify and monitor cut & fill quantities

4. good layout (horizontal & vertical control

5. optimize haul lengths

6. minimize cycle time

7. proper selection and sizing of excavators and haul units

8. experienced personnel in the field

Equipment Functions

• Excavating • Ripping

ESTIMATING EARTHWORK VOLUME

• Excavating

• Loading

• Hauling

• Placing (dumping & spreading)

• Drying

• Ripping

• Boring or tunneling

• Compacting

• Grading

• Finishing