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EAT 360HIGHWAY AND TRANSPORTATION

ENGINEERING

MATERIALS AND PAVEMENTS(Soil Engineering)

LECTURER : MR. ZUHAYR BIN MD. GHAZALY H/P : 014-7170838

TOPICS

Soil characteristics

Basic engineering properties of soils

Classification of soils for highway use

Soil surveys for highway construction

Soil compaction

California Bearing Ratio (CBR) Test

INTRODUCTION

Soil properties - importance when a highway is tocarry high traffic volumes with a large percentageof trucks.

Importance when high embankments - constructedand when the soil is to be strengthened and usedas intermediate support for the highway pavement.

Origin and formation of soils, soil identification, andsoil testing methods.

SOIL CHARACTERISTICS

Origin, formation, grain size, and shape.

Loose mass of mineral and organic materials thatcover the solid crust of granitic and basaltic rocks of

the earth.

Weathering and other geologic processes thatoccur on the surface of the solid rock at or near thesurface of the earth.

Physical and chemical actions, mainly due toatmospheric factors that change the structure andcomposition of the rocks.

SOIL CHARACTERISTICS (CONT.)

Physical weathering - the disintegration of the rocksinto smaller particle sizes by the action of forcesexerted on the rock.

Chemical weathering - result of oxidation,carbonation, and other chemical actions that

decompose the minerals of the rocks.

Residual soils - weathered in place and are locateddirectly above the original material from which they

were formed.

Transported soils - moved by water, wind, glaciers,and so forth, and are located away from theirparent materials.

SOIL CHARACTERISTICS (CONT.)

The texture of a soil - mainly on the shapes and sizesof the soil particles and their distribution in the soilmass.

The individual particles of fine-textured soils -invisible to the naked eye, whereas those of coarse-textured soils - visible to the naked eye.

The distribution of particle size in soils - sieve analysison a soil sample if the particles are sufficiently large.

For soils containing particle sizes smaller than thelower limit, the hydrometer analysis is used.

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BASIC ENGINEERING PROPERTIES OF SOILS

Influence their behaviour when subjected toexternal loads.

Three-phase systems that consist of air, water, andsolids.

BASIC ENGINEERING PROPERTIES OF SOILS (CONT.)

Porosity, n

Void Ratio, e

Moisture Content, w

Degree of Saturation, S

Density of Soil,

Specific Gravity of Soil Particles

BASIC ENGINEERING PROPERTIES OF SOILS (CONT.)

Atterberg limits - water content levels at which thesoil changes from one state to the other.

Shrinkage limit (SL), plastic limit (PL), and liquid limit(LL).

BASIC ENGINEERING PROPERTIES OF SOILS (CONT.)

Permeability - how water flows through the soil -coefficient of permeability (K).

Relationship between the flow velocity and thehydraulic gradient between two points in the soil.

Shear Strength - depends on the cohesion and theangle of internal friction - type of soil.

Triaxial test, the unconfined compression test, or thedirect shear test.

CLASSIFICATION OF SOILS FOR HIGHWAY USE

Systematically categorized according to theirprobable engineering characteristics.

Identifying suitable subbase materials andpredicting the probable behavior of a soil whenused as subgrade material.

Most commonly used classification system forhighway purposes; AASHTO.

CLASSIFICATION OF SOILS FOR HIGHWAY USE

AASHTO Soil Classification System

o based on the Public Roads Classification System.

o determining the relative quality of soils for use in

embankments, subgrades, subbases, and bases.

o seven groups, A-1 through A-7, with several subgroups, as

shown in Table 17.1.

o classification of a given soil is based on its particle size

distribution, LL, and PI.

o group index (GI) of the soils;

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CLASSIFICATION OF SOILS FOR HIGHWAY USE CLASSIFICATION OF SOILS FOR HIGHWAY USE

Unified Soil Classification System (USCS)

o developed during World War II for use in airfield

construction.

o modified several times to obtain the current version which

also can be applied to other types of construction such asdams and foundations.

o the system classifies coarse-grained soils - grain sizecharacteristics and fine-grained soils - plasticity

characteristics.

CLASSIFICATION OF SOILS FOR HIGHWAY USE

CLASSIFICATION OF SOILS FOR HIGHWAY USE SOIL SURVEY FOR HIGHWAY CONSTRUCTION

Investigation of the soil characteristics on thehighway route and the identification of suitable soilsfor use as subbase and fill materials.

First step - collection of existing information on thesoil characteristics of the area in which the highwayis to be located. (geological and agricultural soil

maps, existing aerial photographs)

Obtain and investigate enough soil samples alongthe highway route - identify the boundaries of thedifferent types of soils so that a soil profile can be

drawn. (Auger boring or from test pits for laboratorytesting)

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SOIL SURVEY FOR HIGHWAY CONSTRUCTION

(CONT.)

SOIL SURVEY FOR HIGHWAY CONSTRUCTION

(CONT.)

Geophysical Methods of Soil Exploration

o Resistivity and seismic methods.

o Resistivity method - the difference in electrical conductivity

or resistivity of different types of soils.

o An electrical field is produced in the ground by means of

two current electrodes and the potential drop between the

two intermediate or potential electrodes is then recorded.

o Data for the soil profile are obtained by moving the

electrode along the center line of the proposed highway.

SOIL SURVEY FOR HIGHWAY CONSTRUCTION

(CONT.)

SOIL SURVEY FOR HIGHWAY CONSTRUCTION

(CONT.)

o Seismic method - identify the location of rock profiles or

dense strata underlying softer materials.

o Inducing impact or shock waves into the soil. (either striking

a plate located on the surface with a hammer orexploding small charges in the soil)

o Listening devices known as geophones then pick up theshock waves.

o The time lapse of the wave traveling to the geophone -calculate the velocity of the wave in the surface soil.

o Some of the shock waves can be made to pass from thesurface stratum into underlying layers and then back into

the surface stratum by moving the shock point away from

the geophone.

SOIL SURVEY FOR HIGHWAY CONSTRUCTION

(CONT.)

SOIL SURVEY FOR HIGHWAY CONSTRUCTION

(CONT.)

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SOIL COMPACTION

Proper compaction of the soil will reducesubsequent settlement and volume change to aminimum - enhancing the strength of the

embankment or subbase.

Achieved in the field by using hand-operatedtampers, sheepsfoot rollers, rubber-tired rollers, or

other types of rollers.

Maximum dry density achieved throughcompaction.

At low moisture content, the soil particles are notlubricated - friction between adjacent particlesprevents the densification of the particles.

SOIL COMPACTION (CONT.)

SOIL COMPACTION (CONT.) SOIL COMPACTION (CONT.)

SOIL COMPACTION (CONT.)

Field Compaction Equipment

o two main categories ; spreading the material to the desired

layer or lift thickness - compact each layer of material.

o Spreading equipment - spreading of the material to the

required thickness is done by bulldozers and motor graders.(Figure 17.14)

o Compacting equipment - rollers are used for fieldcompaction and apply either a vibrating force or an

impact force on the soil. (Figure 17.15)

o The equipment used - depend on the size of the project.

SOIL COMPACTION (CONT.)

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SOIL COMPACTION (CONT.) California Bearing Ratio (CBR) Test

Special soil tests that are sometimes undertaken todetermine the strength or supporting value of agiven soil.

Determination of the load-deformation curve of thesoil - standard CBR testing equipment.

Samples of soil compacted to required standards -immersed in water for four days - samples areloaded with a surcharge that simulate the

estimated weight of pavement material the soil willsupport.

Determine the relative strength of a soil with respectto crushed rock.

California Bearing Ratio (CBR) Test (CONT.) California Bearing Ratio (CBR) Test (CONT.)

It does not correctly simulate the shearing forcesimposed on subbase and subgrade materials asthey support highway pavements.

EXAMPLE

The table shows results obtained from a standardAASHTO compaction test on six samples, 4 in.diameter, of a soil to be used as fill for a highway.

Calculate the maximum dry density and theoptimum moisture content of the soil.