1Introduction

Bujang B.K. HuatUniversiti Putra Malaysia, Serdang, Malaysia

David G. TollUniversity of Durham, Durham, United Kingdom

1.1 Aim and scope 31.2 Soils 31.3 Residual soils 41.4 Geographical occurrence of residual soils 41.5 Climate, classification systems and regions 6

Global climate classification systems 6Köppen climate classification system 6Morphoclimatic zones 10

1.6 Distribution of tropical residual soils 121.7 Engineering peculiarities of tropical residual soils 12

Natural slopes subjected to environmental changes 15Stability of vertical or near-vertical excavations 16Lateral earth pressures 17Foundations 18

References 20

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University of Durham, Durham, United KingdomCopyrighted

University of Durham, Durham, United KingdomCopyrighted 1.1 Aim and scope

Copyrighted 1.1 Aim and scope

1.4 Geographical occurrence of residual soils

Copyrighted 1.4 Geographical occurrence of residual soils1.5 Climate, classification systems and regions

Copyrighted 1.5 Climate, classification systems and regionsMaterial

1.4 Geographical occurrence of residual soilsMaterial

1.4 Geographical occurrence of residual soils1.5 Climate, classification systems and regionsMaterial

1.5 Climate, classification systems and regionsGlobal climate classification systems

Material

Global climate classification systemsKöppen climate classification system

Material Köppen climate classification system

1.6 Distribution of tropical residual soils

Material 1.6 Distribution of tropical residual soils

Material 1.7 Engineering peculiarities of tropical residual soils

Material 1.7 Engineering peculiarities of tropical residual soilsNatural slopes subjected to environmental changes

Material Natural slopes subjected to environmental changes- Natural slopes subjected to environmental changes- Natural slopes subjected to environmental changesStability of vertical or near-vertical excavations

- Stability of vertical or near-vertical excavationsTaylor

Natural slopes subjected to environmental changesTaylor

Natural slopes subjected to environmental changesTaylor

Stability of vertical or near-vertical excavationsTaylor

Stability of vertical or near-vertical excavations

& Francis

Introduction 3

1.1 AIM AND SCOPE

Residual soils are found in many parts of the world and are extensively used in the con-struction of foundations and as a construction material. In tropical areas, residual soillayers are often extensive and may measure a few hundred meters until unweatheredrock is reached. As the major soil and foundation engineering conditions are deter-mined by this type of soil, evidently all aspects should be known before the engineeringwork is started.

The Handbook of Tropical Residual Soil Engineering is intended as a completereference source and manual for every engineer working on or interested in soil andfoundation engineering in tropical areas. Almost every aspect of tropical residual soilsis treated, including major applications, and a dedicated part is focused on region- andcountry-specific sections, including typical characteristics and soil conditions. Sometables and charts with typical data are included. This book includes among others thefollowing topics: the genesis and classification of residual soils, the role of climate insoil formation (in particular tropical residual soil and why residual soils are different),the sampling and testing of tropical residual soils, the behaviour of weakly bondedand unsaturated soils, and the volume change and shear strength of tropical residualsoils. There is a section on engineering applications of tropical residual soils such asin slopes and foundations. The book also features regional/country case studies wherethese soils are found, such as Hong Kong, India and Southeast Asia.

This unique handbook will constitute an invaluable reference and should be astandard work in the library of any engineer involved in geological, foundation andconstruction engineering work in tropical residual soil.

1.2 SOILS

Soils constitute the multi-phased interface stratum formed by the interaction of thelithosphere with the atmosphere, hydrosphere and biosphere. This dynamism may beexpressed through the metaphor of the Earth as an engine where the atmosphere is theworking fluid of the Earth’s heat engine (Ingersoll, 1983). This drives the dynamicson the terrestrial surface as expressed through the operation of physical and chemicalprocesses at the Earth’s surface resulting in the formation of soils.

Soils form a mantle of unconsolidated superficial cover that is variable in thickness.This is due to the fact that the depths to which the terrestrial materials, namely rocks,have been altered to form soils vary as a function of factors such as climate, topographyand the nature of the subsurface. It is also due to the varying thickness of transportedmaterials that come to form the unconsolidated superficial cover.

Soils may, therefore, be grouped into two broad categories: residual and trans-ported soils. Residual soils form or accumulate and remain at the place where they areformed. Transported soils are formed from materials originating elsewhere that havemoved to the present site, where they constitute the unconsolidated superficial layer.

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rock is reached. As the major soil and foundation engineering conditions are deter-Copyrighted

rock is reached. As the major soil and foundation engineering conditions are deter-mined by this type of soil, evidently all aspects should be known before the engineeringCopyrighted

mined by this type of soil, evidently all aspects should be known before the engineeringwork is started.

Copyrighted

work is started.The Handbook of Tropical Residual Soil Engineering is intended as a complete

Copyrighted

The Handbook of Tropical Residual Soil Engineering is intended as a completereference source and manual for every engineer working on or interested in soil and

Copyrighted

reference source and manual for every engineer working on or interested in soil andfoundation engineering in tropical areas. Almost every aspect of tropical residual soils

Copyrighted

foundation engineering in tropical areas. Almost every aspect of tropical residual soilsis treated, including major applications, and a dedicated part is focused on region- and

Copyrighted is treated, including major applications, and a dedicated part is focused on region- andcountry-specific sections, including typical characteristics and soil conditions. Some

Copyrighted country-specific sections, including typical characteristics and soil conditions. Sometables and charts with typical data are included. This book includes among others the

Copyrighted tables and charts with typical data are included. This book includes among others thefollowing topics: the genesis and classification of residual soils, the role of climate in

Copyrighted following topics: the genesis and classification of residual soils, the role of climate insoil formation (in particular tropical residual soil and why residual soils are different),

Copyrighted soil formation (in particular tropical residual soil and why residual soils are different),Material

following topics: the genesis and classification of residual soils, the role of climate inMaterial

following topics: the genesis and classification of residual soils, the role of climate insoil formation (in particular tropical residual soil and why residual soils are different),Material

soil formation (in particular tropical residual soil and why residual soils are different),the sampling and testing of tropical residual soils, the behaviour of weakly bonded

Material

the sampling and testing of tropical residual soils, the behaviour of weakly bondedand unsaturated soils, and the volume change and shear strength of tropical residual

Material and unsaturated soils, and the volume change and shear strength of tropical residualsoils. There is a section on engineering applications of tropical residual soils such as

Material soils. There is a section on engineering applications of tropical residual soils such asin slopes and foundations. The book also features regional/country case studies where

Material in slopes and foundations. The book also features regional/country case studies wherethese soils are found, such as Hong Kong, India and Southeast Asia.

Material these soils are found, such as Hong Kong, India and Southeast Asia.- This unique handbook will constitute an invaluable reference and should be a- This unique handbook will constitute an invaluable reference and should be aTaylor

This unique handbook will constitute an invaluable reference and should be aTaylor

This unique handbook will constitute an invaluable reference and should be astandard work in the library of any engineer involved in geological, foundation andTaylor

standard work in the library of any engineer involved in geological, foundation andconstruction engineering work in tropical residual soil.

Taylor construction engineering work in tropical residual soil.

Taylor & & Soils constitute the multi-phased interface stratum formed by the interaction of the& Soils constitute the multi-phased interface stratum formed by the interaction of theFrancis

Soils constitute the multi-phased interface stratum formed by the interaction of theFrancis

Soils constitute the multi-phased interface stratum formed by the interaction of thelithosphere with the atmosphere, hydrosphere and biosphere. This dynamism may be

Francislithosphere with the atmosphere, hydrosphere and biosphere. This dynamism may beexpressed through the metaphor of the Earth as an engine where the atmosphere is the

Francisexpressed through the metaphor of the Earth as an engine where the atmosphere is theworking fluid of the Earth’s heat engine (Ingersoll, 1983). This drives the dynamics

Francisworking fluid of the Earth’s heat engine (Ingersoll, 1983). This drives the dynamics

Francison the terrestrial surface as expressed through the operation of physical and chemical

Francison the terrestrial surface as expressed through the operation of physical and chemical

4 Handbook of tropical residual soils engineering

The physical processes involved in the operation of their agents of transportation,i.e. gravity, wind, water etc., have dislodged, eroded and transported soil particles totheir present location.

1.3 RESIDUAL SOILS

According to McCarthy (1993), residual soils are those that form from rock or accu-mulation of organic material and remain at the place where they were formed. Thisentire unconsolidated superficial cover is referred to as soil (Press and Siever, 1994).However, according to Bland and Rolls (1998) this mantle is also termed the regolith,which is separated into an upper part, referred to as soil, and the portion below it andabove the bedrock, called the saprolite. The regolith is chemically altered, especiallyin humid tropical regions. There are, however, a variety of definitions of residual soils,indicating a diversity of understanding of what are perceived as residual soils.

Brand and Philipson (1985) define residual soil as ‘a soil formed by weathering inplace, but with the original rock texture completely destroyed’. This term is commonlyused in a wider sense to include highly or completely decomposed rock, which is anengineering material and behaves like a soil in places such as Hong Kong. Blight(1985) gave the definition of residual soil in South Africa as all material of a soil-like consistency that is located below the local ancient erosion surface, i.e. below thepebble marker. The exceptions are the extensive deposits of ancient windblown desertsands with some cohesion. Materials of this type are also considered to be residualsoils. Soil reworked in-situ by termites is also strictly residual and not transportedmaterial. Sowers (1985) defined residual soil as the product of rock weathering thatremains in place above the yet-to-be-weathered parent rock. The boundary betweenrock and soil is arbitrary and often misleading. There is a graduation of propertiesand no sharp boundaries within the weathering profile. The Public Works Institute ofMalaysia (1996) defines residual soil as ‘a soil which has been formed in-situ by thedecomposition of parent material and which has not been transported any significantdistance’ and defines tropical residual soil as ‘a soil formed in-situ under tropicalweathering conditions’. Other workers echo the above definitions as soil formed in-situby the weathering of rocks whereby the original rock texture is completely destroyed,or soil formed by weathering in places where the original rock is completely destroyednearer the surface. The rocks have totally disintegrated and the mass behaves like a soil.

Compositionally, the solid phase is constituted not only from the residue of unal-tered terrestrial material but also from the products of the interaction of terrestrialmaterial with the agents of surface processes. In addition, there are aqueous (water)and gaseous phases. That portion, normally the upper regolith that supports plant life,also includes organic matter (both living and dead).

1.4 GEOGRAPHICAL OCCURRENCE OF RESIDUAL SOILS

Residual soils occur in all parts of the world on various types of rocks as shown inFigure 1.1(a)–(d). Conditions conducive to the formation of chemically weatheredresidual soils are not present in temperate zones but extensive remnant deposits ofsuch soils are found from periods when hot, humid conditions existed (Brand andPhilipson, 1985).

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which is separated into an upper part, referred to asCopyrighted

which is separated into an upper part, referred to asabove the bedrock, called theCopyrighted

above the bedrock, called thein humid tropical regions. There are, however, a variety of definitions of residual soils,

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in humid tropical regions. There are, however, a variety of definitions of residual soils,indicating a diversity of understanding of what are perceived as residual soils.

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indicating a diversity of understanding of what are perceived as residual soils.Brand and Philipson (1985) define residual soil as ‘a soil formed by weathering in

Copyrighted

Brand and Philipson (1985) define residual soil as ‘a soil formed by weathering inplace, but with the original rock texture completely destroyed’. This term is commonly

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place, but with the original rock texture completely destroyed’. This term is commonlyused in a wider sense to include highly or completely decomposed rock, which is an

Copyrighted used in a wider sense to include highly or completely decomposed rock, which is anengineering material and behaves like a soil in places such as Hong Kong. Blight

Copyrighted engineering material and behaves like a soil in places such as Hong Kong. Blight(1985) gave the definition of residual soil in South Africa as all material of a soil-

Copyrighted (1985) gave the definition of residual soil in South Africa as all material of a soil-like consistency that is located below the local ancient erosion surface, i.e. below the

Copyrighted like consistency that is located below the local ancient erosion surface, i.e. below theMaterial

like consistency that is located below the local ancient erosion surface, i.e. below theMaterial

like consistency that is located below the local ancient erosion surface, i.e. below thepebble marker. The exceptions are the extensive deposits of ancient windblown desert

Material

pebble marker. The exceptions are the extensive deposits of ancient windblown desertsands with some cohesion. Materials of this type are also considered to be residual

Material

sands with some cohesion. Materials of this type are also considered to be residualsoils. Soil reworked in-situ by termites is also strictly residual and not transported

Material soils. Soil reworked in-situ by termites is also strictly residual and not transportedmaterial. Sowers (1985) defined residual soil as the product of rock weathering that

Material material. Sowers (1985) defined residual soil as the product of rock weathering thatremains in place above the yet-to-be-weathered parent rock. The boundary between

Material remains in place above the yet-to-be-weathered parent rock. The boundary betweenrock and soil is arbitrary and often misleading. There is a graduation of properties

Material rock and soil is arbitrary and often misleading. There is a graduation of properties- rock and soil is arbitrary and often misleading. There is a graduation of properties- rock and soil is arbitrary and often misleading. There is a graduation of propertiesand no sharp boundaries within the weathering profile. The Public Works Institute of

- and no sharp boundaries within the weathering profile. The Public Works Institute ofTaylor

rock and soil is arbitrary and often misleading. There is a graduation of propertiesTaylor

rock and soil is arbitrary and often misleading. There is a graduation of propertiesTaylor

and no sharp boundaries within the weathering profile. The Public Works Institute ofTaylor

and no sharp boundaries within the weathering profile. The Public Works Institute ofMalaysia (1996) defines residual soil as ‘a soil which has been formed in-situ by the

Taylor Malaysia (1996) defines residual soil as ‘a soil which has been formed in-situ by thedecomposition of parent material and which has not been transported any significant

Taylor decomposition of parent material and which has not been transported any significantdistance’ and defines tropical residual soil as ‘a soil formed in-situ under tropical

Taylor distance’ and defines tropical residual soil as ‘a soil formed in-situ under tropicalweathering conditions’. Other workers echo the above definitions as soil formed in-situ

Taylor weathering conditions’. Other workers echo the above definitions as soil formed in-situby the weathering of rocks whereby the original rock texture is completely destroyed,

Taylor by the weathering of rocks whereby the original rock texture is completely destroyed,& weathering conditions’. Other workers echo the above definitions as soil formed in-situ& weathering conditions’. Other workers echo the above definitions as soil formed in-situby the weathering of rocks whereby the original rock texture is completely destroyed,& by the weathering of rocks whereby the original rock texture is completely destroyed,or soil formed by weathering in places where the original rock is completely destroyed

& or soil formed by weathering in places where the original rock is completely destroyedFrancis

or soil formed by weathering in places where the original rock is completely destroyedFrancis

or soil formed by weathering in places where the original rock is completely destroyednearer the surface. The rocks have totally disintegrated and the mass behaves like a soil.

Francisnearer the surface. The rocks have totally disintegrated and the mass behaves like a soil.

FrancisCompositionally, the solid phase is constituted not only from the residue of unal-

FrancisCompositionally, the solid phase is constituted not only from the residue of unal-

tered terrestrial material but also from the products of the interaction of terrestrial

Francistered terrestrial material but also from the products of the interaction of terrestrialmaterial with the agents of surface processes. In addition, there are aqueous (water)

Francismaterial with the agents of surface processes. In addition, there are aqueous (water)and gaseous phases. That portion, normally the upper regolith that supports plant life,

Francisand gaseous phases. That portion, normally the upper regolith that supports plant life,

Figure 1.1a Residual soils developed from sedimentary rocks (After Rollings and Rollings, 1996)

Figure 1.1b Residual soils developed from intrusive igneous rocks, primary granitic shields andmountains (After Rollings and Rollings, 1996)

Figure 1.1c Residual soils developed from extrusive igneous rocks, primary basaltic plateaus andmountains (After Rollings and Rollings, 1996)

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Figure 1.1a

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Figure 1.1a Residual soils developed from sedimentary rocks (

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Residual soils developed from sedimentary rocks (

Copyrighted Material - Taylor

Taylor Residual soils developed from intrusive igneous rocks, primary granitic shields and

Taylor Residual soils developed from intrusive igneous rocks, primary granitic shields and& Residual soils developed from intrusive igneous rocks, primary granitic shields and& Residual soils developed from intrusive igneous rocks, primary granitic shields and& Francis

Francis

6 Handbook of tropical residual soils engineering

Figure 1.1d Residual soils developed from metamorphic rocks (After Rollings and Rollings, 1996)

1.5 CLIMATE, CLASSIFICATION SYSTEMS AND REGIONS

Global climate classif ication systems

The different climates of the world, referred to as climatic types, enable a global climateclassification based on identical characteristics, and areas experiencing similar climatesare grouped as climatic regions. There is no single universal climate classificationsystem. The climate classifications devised are either genetic classifications based uponmechanisms such as net radiation, thermal regimes or air-mass dominance over aregion, or empirical classifications based on recorded data such as temperature andprecipitation. The Köppen climate classification system, an empirical classificationsystem, is the most widely used system for classifying the world’s climates.

Köppen climate classif ication system

This system is based on the mean annual and monthly averages of temperature andprecipitation, combined and compared in a variety of ways. It defines five climaticregions based on thermal criteria (temperature) and only one based on moisture aslisted in Table 1.1.

The Köppen system uses the capital letters A, B, C, D, E and H to designate theseclimatic categories, with additional letters to further signify specific temperature andmoisture conditions as illustrated in Table 1.2. The global distribution of the systemis shown in Figure 1.2.

Areas with tropical climates (the A category climate in the Köppen classificationsystem) are extensive, occurring in almost all continents between latitudes 20◦N to20◦S of the equator as illustrated in Figure 1.3. The key criterion for an A category

Copyrighted

Copyrighted Residual soils developed from metamorphic rocks (

Copyrighted Residual soils developed from metamorphic rocks (Material

Residual soils developed from metamorphic rocks (Material

Residual soils developed from metamorphic rocks (

1.5 CLIMATE, CLASSIFICATION SYSTEMS AND REGIONS

Material 1.5 CLIMATE, CLASSIFICATION SYSTEMS AND REGIONS

Material - The different climates of the world, referred to as climatic types, enable a global climate- The different climates of the world, referred to as climatic types, enable a global climateTaylor

The different climates of the world, referred to as climatic types, enable a global climateTaylor

The different climates of the world, referred to as climatic types, enable a global climateclassification based on identical characteristics, and areas experiencing similar climatesTaylor

classification based on identical characteristics, and areas experiencing similar climatesare grouped as climatic regions. There is no single universal climate classification

Taylor are grouped as climatic regions. There is no single universal climate classificationsystem. The climate classifications devised are either genetic classifications based upon

Taylor system. The climate classifications devised are either genetic classifications based upon

Taylor mechanisms such as net radiation, thermal regimes or air-mass dominance over a

Taylor mechanisms such as net radiation, thermal regimes or air-mass dominance over aregion, or empirical classifications based on recorded data such as temperature and

Taylor region, or empirical classifications based on recorded data such as temperature and& region, or empirical classifications based on recorded data such as temperature and& region, or empirical classifications based on recorded data such as temperature andprecipitation. The Köppen climate classification system, an empirical classification

& precipitation. The Köppen climate classification system, an empirical classificationsystem, is the most widely used system for classifying the world’s climates.

& system, is the most widely used system for classifying the world’s climates.Francis

precipitation. The Köppen climate classification system, an empirical classificationFrancis

precipitation. The Köppen climate classification system, an empirical classificationsystem, is the most widely used system for classifying the world’s climates.Francis

system, is the most widely used system for classifying the world’s climates.FrancisThis system is based on the mean annual and monthly averages of temperature and

FrancisThis system is based on the mean annual and monthly averages of temperature andprecipitation, combined and compared in a variety of ways. It defines five climatic

Francisprecipitation, combined and compared in a variety of ways. It defines five climatic

Introduction 7

Table 1.1 The Köppen climatic regions

Category Climate region

Based on temperatureA Tropical moist (equatorial regions)C Moist mid-latitude with mild winters (Mediterranean, humid subtropical)D Moist mid-latitude with cold winters (humid continental, subarctic)E Polar with extremely cold winters and summers (polar regions)H Highland (cool to cold, found in mountains and high plateaus)Based on moistureB Dry with deficient precipitation through most of the year (deserts and steppes)

Table 1.2 Modified Köppen climatic classification (After Bergman and McKnight, 1993)

Letters

1st 2nd 3rd Description Definition Types

A Low-latitude humidclimates

Average temperature ofeach month above 18◦C

Tropical wet (Af )Tropical monsoonal (Am)

f No dry season Average rainfall of eachmonth at least 6 cm

Tropical savanna (Aw)

m Monsoonal; short dryseason compensatedby heavy rains inother months

1 to 3 months withaverage rainfallless than 6 cm

w Dry season in ‘winter’(low sun season)

3 to 6 months with averagerainfall less than 6 cm

B Dry climates;evaporation exceedsprecipitation

Subtropical desert (Bwh)Subtropical steppe (Bsh)

w Arid climates;‘truedeserts’

Average annualprecipitation less thanabout 38 cm in lowlatitudes; 25 cm inmid-latitudes

Mid-latitude desert (Bwk)Mid-latitude steppe (Bsk)

s Semiarid climates;steppe

Average annualprecipitation betweenabout 38 cm and 76 cmin low latitudes; betweenabout 25 cm and 64 cmin mid-latitudes;without pronouncedseasonal concentration

h Low-latitude dryclimate

Average annualtemperature morethan 18◦C

k Mid-latitude dryclimate

Average annualtemperature lessthan 18◦C

(Continued)

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B Dry with deficient precipitation through most of the year (deserts and steppes)Copyrighted

B Dry with deficient precipitation through most of the year (deserts and steppes)Copyrighted

Modified Köppen climatic classification (

Copyrighted

Modified Köppen climatic classification (

Copyrighted 1st 2nd 3rd Description

Copyrighted 1st 2nd 3rd Description

Copyrighted Low-latitude humid

Copyrighted Low-latitude humidMaterial

Material

Low-latitude humidMaterial

Low-latitude humid

f No dry season Average rainfall of each

Material

f No dry season Average rainfall of eachmonth at least 6 cm

Material month at least 6 cm1 to 3 months with

Material 1 to 3 months withaverage rainfall

Material average rainfallless than 6 cm

Material less than 6 cm- 3 to 6 months with average- 3 to 6 months with averageTaylor

3 to 6 months with averageTaylor

3 to 6 months with averagerainfall less than 6 cm

Taylor rainfall less than 6 cm

& Mid-latitude desert (Bwk)& Mid-latitude desert (Bwk)Mid-latitude steppe (Bsk)

& Mid-latitude steppe (Bsk)Francis

Mid-latitude steppe (Bsk)Francis

Mid-latitude steppe (Bsk)

Table 1.2 Continued

Letters

1st 2nd 3rd Description Definition Types

C Mild mid-latitudedry climates

Average temperature ofcoldest month between18◦C and −3◦C; averagetemperature of warmestmonth above 10◦C

Mediterranean(Csa, Csb)Humid subtropical(Cfa, Cwa)

s Dry summer Driest summer monthhas less than 1/3 theaverage precipitation ofwettest winter month

Marine west coast(Cfb,Cfc)

w Dry winter Driest winter monthhas less than 1/10 theaverage precipitation ofwettest summer month

f No dry season Does not fit either s orw above

a Hot summers Average temperature ofwarmest month morethan 22◦C

b Warm summers Average temperature ofwarmest month below22◦C; at least 4 monthswith averagetemperature above 10◦C

c Cool summers Average temperature ofwarmest month below22◦C; less than 4 monthswith averagetemperature above 10◦C

D Humid mid-latitudeclimates with severewinters

4 to 8 months withaverage temperaturemore than 10◦C

2nd and 3rd letters same as in C climatesd Very cold winters Average temperature of

coldest month less than−38◦C

E Polar climates; notrue summer

No month with averagetemperature more than10◦C

Humid continental(Dfa, Dfb, Dwa, Dwb)Subarctic (Dfc, Dfd,Dwc, Dwd)

T Tundra climates At least one month withaverage temperaturemore than 0◦C but lessthan 10◦C

Tundra (ET)

F Ice cap climates No month with averagetemperature more than0◦C

Ice cap (EF)

H Highland climates Significant climaticchanges within shorthorizontal distances dueto altitudinal variations

Highland (H)

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w Dry winter Driest winter month

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w Dry winter Driest winter month

f No dry season Does not fit either s or

Copyrighted

f No dry season Does not fit either s or

a Hot summers Average temperature of

Copyrighted a Hot summers Average temperature of

b Warm summers Average temperature of

Copyrighted b Warm summers Average temperature ofMaterial

b Warm summers Average temperature ofMaterial

b Warm summers Average temperature of

temperature above 10

Material temperature above 10

c Cool summers Average temperature of

Material c Cool summers Average temperature of

warmest month below

Material warmest month below22

Material 22- C; less than 4 months- C; less than 4 monthswith average- with averageTaylor

with averageTaylor

with averagetemperature above 10Taylor

temperature above 10

4 to 8 months with

Taylor 4 to 8 months withaverage temperature

Taylor average temperaturemore than 10

Taylor more than 10◦

Taylor ◦C

Taylor C

d Very cold winters Average temperature of

Taylor d Very cold winters Average temperature of& d Very cold winters Average temperature of& d Very cold winters Average temperature of

coldest month less than& coldest month less than Francis

Humid continental

FrancisHumid continental(Dfa, Dfb, Dwa, Dwb)

Francis(Dfa, Dfb, Dwa, Dwb)

FrancisSubarctic (Dfc, Dfd,

FrancisSubarctic (Dfc, Dfd,Dwc, Dwd)

FrancisDwc, Dwd)Tundra (ET)

FrancisTundra (ET)

MoisttropicalclimatesDryclimates

Moistclimateswith mildwinters

MoistclimateswithseverewintersPolarclimates

Highlandclimates

A Af Tropical rain forestTropical monsoonTropical wet-and-dry

Arid desert

Semi-arid or steppe

Humid subtropical

Highland

MarineMediterranean(dry summer)Dry winter

Polar ice cap

Polar tundra

Subpolar

Humid continental

Dry winter

AmAw

BW

BS

Cfa

CfbCfcCs

CwDfaDfbDfcDfdDw

ET

EF

H

B

C

D

E

H

Figure 1.2 Global distribution of the Köppen classification system(Source: http://calspace.ucsd.edu/virtualmuseum/climatechange1/07_1.shtml)

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DryCopyrighted

DryclimatesCopyrighted

climates

Moist

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Moistclimates

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climateswith mild

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with mildwinters

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winters

Polar ice cap

Copyrighted Polar ice cap

Polar tundra

Copyrighted Polar tundra

Subpolar

Copyrighted Subpolar

Humid continental

Copyrighted Humid continental

Dry winter

Copyrighted Dry winter

Cw

Copyrighted

CwDfa

Copyrighted

DfaDfb

Copyrighted DfbDfc

Copyrighted DfcDfd

Copyrighted DfdDw

Copyrighted Dw

BCopyrighted

B

C

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C

Copyrighted Material

Material

Material

Polar ice capMaterial

Polar ice cap

- Taylor & Francis

10 Handbook of tropical residual soils engineering

Tropic of Cancer

Tropic of Capricorn

Equator

Figure 1.3 Areas with a tropical climate(Source: World Wide Web)

climate is for the coolest month to have a temperature of more than 18◦C, makingit the only truly winterless climate category in the world. The consistent day lengthand near-perpendicular angle of the sun throughout the year generates temperaturesabove 18◦C. Another characteristic is the prevalence of moisture. As warm, moistand unstable air masses dominate the oceans at these latitudes, this climate zone hasabundant sources of moisture, giving rise to high humidity. The tropical climate isfurther classified into three types on the basis of the quantity and regime of annualrainfall:

a) Tropical wet type (Af) – experiences relatively abundant rainfall in every monthof the year.

b) Tropical monsoonal type (Am) – has a short dry season but a very rainy wetseason.

c) Tropical savanna type (Aw) – is characterised by a longer dry season and aprominent but not extraordinary wet season.

Morphoclimatic zones

The climatic system fuels the Earth’s exogenic processes and creates the landscape.The different climates dictating the respective geomorphic processes that operate in theregions have led geomorphologists to suggest that these different climates are associatedwith characteristic landform assemblages. These landforms are termed as belongingto morphoclimatic zones. The climatic elements and the relative importance of geo-morphologic processes for the various delineated morphological zones are describedin Table 1.3. Figure 1.4 shows the geographical distribution of these zones.

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Copyrighted

Copyrighted Figure 1.3

Copyrighted Figure 1.3

Material

climate is for the coolest month to have a temperature of more than 18

Material

climate is for the coolest month to have a temperature of more than 18it the only truly winterless climate category in the world. The consistent day length

Material it the only truly winterless climate category in the world. The consistent day lengthand near-perpendicular angle of the sun throughout the year generates temperatures

Material and near-perpendicular angle of the sun throughout the year generates temperatures

C. Another characteristic is the prevalence of moisture. As warm, moist

Material C. Another characteristic is the prevalence of moisture. As warm, moistand unstable air masses dominate the oceans at these latitudes, this climate zone has

Material and unstable air masses dominate the oceans at these latitudes, this climate zone has- and unstable air masses dominate the oceans at these latitudes, this climate zone has- and unstable air masses dominate the oceans at these latitudes, this climate zone hasabundant sources of moisture, giving rise to high humidity. The tropical climate is

- abundant sources of moisture, giving rise to high humidity. The tropical climate isTaylor

abundant sources of moisture, giving rise to high humidity. The tropical climate isTaylor

abundant sources of moisture, giving rise to high humidity. The tropical climate isfurther classified into three types on the basis of the quantity and regime of annual

Taylor further classified into three types on the basis of the quantity and regime of annual

Taylor a) Tropical wet type (Af) – experiences relatively abundant rainfall in every month

Taylor a) Tropical wet type (Af) – experiences relatively abundant rainfall in every month& a) Tropical wet type (Af) – experiences relatively abundant rainfall in every month& a) Tropical wet type (Af) – experiences relatively abundant rainfall in every month

b) Tropical monsoonal type (Am) – has a short dry season but a very rainy wet

& b) Tropical monsoonal type (Am) – has a short dry season but a very rainy wetFrancis

b) Tropical monsoonal type (Am) – has a short dry season but a very rainy wetFrancis

b) Tropical monsoonal type (Am) – has a short dry season but a very rainy wetFrancisc) Tropical savanna type (Aw) – is characterised by a longer dry season and a

Francisc) Tropical savanna type (Aw) – is characterised by a longer dry season and a

Introduction 11

Table 1.3 The Earth’s major morphoclimatic zones (After Summerfield, 1996)

Mean annual Mean annualMorphoclimatic temperature precipitationzone (◦C) (mm) Relative importance of geomorphic processes

Tropicalhumid

20–30 >1500 High potential rates of chemical weathering;mechanical weathering limited; active, highlyepisodic mass movement; moderate tolow rates of stream corrosion but locallyhigh rates of dissolved and suspendedload transport

Tropicalwet-dry

20–30 600–1500 Chemical weathering active during wet season;rates of mechanical weathering low to moderate;mass movement fairly active; fluvial action highduring wet season with overland and channel flow;wind action generally minimal but locally moderatein dry season

Tropicalsemi-arid

10–30 300–600 Chemical weathering rates moderate to low;mechanical weathering locally active, especially ondrier and cooler margins; mass movement locallyactive but sporadic; fluvial action rates high butepisodic; wind action moderate to high

Tropicalarid

10–30 0–300 Mechanical weathering rates high (especiallysalt weathering); chemical weathering minimal;mass movement minimal; rates of fluvial activitygenerally very low but sporadically high;wind action at a maximum

Humidmid-latitude

0–20 400–1800 Chemical weathering rates moderate, increasingto high at lower latitudes; mechanical weatheringactivity moderate with frost action important inhigher fluvial processes; wind action confined tocoasts

Drycontinental

0–10 100–400 Chemical weathering rates low to moderate;mechanical weathering, especially frost action,seasonally active; mass movement moderate andepisodic; fluvial processes active in wet season;wind action locally moderate

Periglacial <0 100–1000 Mechanical weathering very active with frostaction at a maximum; chemical weathering rateslow to moderate; mass movement very active;fluvial processes seasonally active; wind actionrates locally high

Glacial <0 0–1000 Mechanical weathering rates (especially frostaction) high; chemical weathering rates low; massmovement rates low except locally; fluvial actionconfined to seasonal melt; glacial action at amaximum; wind action significant

Azonalmountainzone

Highly variable Highly variable Rates of all processes vary significantly withaltitude; mechanical and glacial action significantat high elevations

Copyrighted

TropicalCopyrighted

Tropicalwet-dry

Copyrighted

wet-dry

10–30 300–600 Chemical weathering rates moderate to low;

Copyrighted 10–30 300–600 Chemical weathering rates moderate to low;

Material

10–30 0–300 Mechanical weathering rates high (especially

Material

10–30 0–300 Mechanical weathering rates high (especially

mass movement minimal; rates of fluvial activity

Material mass movement minimal; rates of fluvial activitygenerally very low but sporadically high;

Material generally very low but sporadically high;wind action at a maximum

Material wind action at a maximum

0–20 400–1800 Chemical weathering rates moderate, increasing

Material 0–20 400–1800 Chemical weathering rates moderate, increasing- 0–20 400–1800 Chemical weathering rates moderate, increasing- 0–20 400–1800 Chemical weathering rates moderate, increasingto high at lower latitudes; mechanical weathering

- to high at lower latitudes; mechanical weatheringTaylor

0–20 400–1800 Chemical weathering rates moderate, increasingTaylor

0–20 400–1800 Chemical weathering rates moderate, increasingto high at lower latitudes; mechanical weatheringTaylor

to high at lower latitudes; mechanical weatheringactivity moderate with frost action important in

Taylor

activity moderate with frost action important inhigher fluvial processes; wind action confined to

Taylor higher fluvial processes; wind action confined to

0–10 100–400 Chemical weathering rates low to moderate;

Taylor 0–10 100–400 Chemical weathering rates low to moderate;mechanical weathering, especially frost action,

Taylor mechanical weathering, especially frost action,seasonally active; mass movement moderate and

Taylor seasonally active; mass movement moderate and& mechanical weathering, especially frost action,& mechanical weathering, especially frost action,seasonally active; mass movement moderate and& seasonally active; mass movement moderate andepisodic; fluvial processes active in wet season;

& episodic; fluvial processes active in wet season;Francis

seasonally active; mass movement moderate andFrancis

seasonally active; mass movement moderate andepisodic; fluvial processes active in wet season;Francis

episodic; fluvial processes active in wet season;wind action locally moderate

Francis

wind action locally moderateFrancis

0 100–1000 Mechanical weathering very active with frost

Francis0 100–1000 Mechanical weathering very active with frost

action at a maximum; chemical weathering rates

Francisaction at a maximum; chemical weathering rateslow to moderate; mass movement very active;

Francislow to moderate; mass movement very active;fluvial processes seasonally active; wind action

Francisfluvial processes seasonally active; wind action

12 Handbook of tropical residual soils engineering

Humid tropical

Tropical wet-dry

Humid mid-latitude

Dry continental

Tropical semi-arid

Tropical arid

Periglacial

1000 10000km

105 km2106 km2

Glacial

Mountains (altitudinal zonation important)

Figure 1.4 Global distribution of morphoclimatic zones (After Summerfield, 1996)

1.6 DISTRIBUTION OF TROPICAL RESIDUAL SOILS

The distribution of tropical residual soils is shown in Figure 1.5. Large expanses ofresidual soils to great depths are normally found in the tropical humid regions, e.g.Northern Brazil, Ghana, Malaysia, Nigeria, Southern India, Sri Lanka, Singapore andthe Philippines, due to active weathering leading to residual soil formation.

1.7 ENGINEERING PECULIARITIES OF TROPICAL RESIDUAL SOILS

The term ‘soil’ in engineering is commonly used to refer to any kind of loose, uncon-solidated natural material enveloping the surface that is relatively easy to separate byeven gentle means (Terzaghi and Peck, 1967). According to Johnson and De Graff(1988), any mineral that lacks high strength is considered a soil. As a consequence,both the above two types of unconsolidated superficial cover are referred to as soil.The residual soils found in the tropics form the main subject matter of this book.

Copyrighted

Copyrighted

Copyrighted Material Humid mid-latitude

Material Humid mid-latitude

Dry continental

Material Dry continental

- - Taylor

Taylor Global distribution of morphoclimatic zones (

Taylor Global distribution of morphoclimatic zones (

& 1.6 DISTRIBUTION OF TROPICAL RESIDUAL SOILS& 1.6 DISTRIBUTION OF TROPICAL RESIDUAL SOILSFrancis

FrancisThe distribution of tropical residual soils is shown in Figure 1.5. Large expanses of

FrancisThe distribution of tropical residual soils is shown in Figure 1.5. Large expanses of

Francisresidual soils to great depths are normally found in the tropical humid regions, e.g.

Francisresidual soils to great depths are normally found in the tropical humid regions, e.g.Northern Brazil, Ghana, Malaysia, Nigeria, Southern India, Sri Lanka, Singapore and

FrancisNorthern Brazil, Ghana, Malaysia, Nigeria, Southern India, Sri Lanka, Singapore andthe Philippines, due to active weathering leading to residual soil formation.

Francisthe Philippines, due to active weathering leading to residual soil formation.

Introduction 13

1.

2.

3.4.

Ferrallitic soils

Cancer

Equator

Capricorn

Fersiallitic soils

AndosolsVertisols

Figure 1.5 Distribution of tropical residual soils (After Bell, 2000)

Residual soils are generally located above the groundwater table. The soils aretherefore generally unsaturated and possess negative pore water pressures. Climaticchanges (i.e. evaporation and infiltration) and transpiration influence the water contentand the negative pore-water pressure of the unsaturated soils, especially those locatedclose to the ground surface. As a result, the hydraulic properties, shear strength andvolume of the soil vary in response to the climatic changes. The traditional practicesof soil mechanics have undergone significant changes during the past few decades.Some of these changes are related to increased attention being given to the unsaturatedsoil zone above the groundwater table. The computational capability available to thegeotechnical engineer has strongly influenced the engineer’s ability to address thesecomplex problems. The unsaturated soil zone is subjected to a flux-type boundarycondition for many of the problems faced by geotechnical engineers. Unsaturated soilmechanics has become a necessary tool for analyzing the behaviour of soils in thiszone.

The behaviour of numerous materials encountered in engineering practice is notconsistent with the principles and concepts of classical, saturated soil mechanics.Commonly, it is the presence of more than two phases that results in a material that isdifficult to deal with in engineering practice. Soils that are unsaturated form the largestcategory of materials which do not adhere to the behaviour of classical, saturated soilmechanics. An unsaturated soil has more than two phases, and the pore-water pressureis negative relative to the pore-air pressure. Any soil present near the ground surfacein a relatively dry environment will be subjected to negative pore-water pressures andpossible desaturation. The process of excavating, remolding and recompacting a soilalso results in unsaturated material. The resulting materials form a large category of

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Copyrighted 4.

Copyrighted 4.

Distribution of tropical residual soils (

Copyrighted Distribution of tropical residual soils (Material

Distribution of tropical residual soils (Material

Distribution of tropical residual soils (

Residual soils are generally located above the groundwater table. The soils are

Material Residual soils are generally located above the groundwater table. The soils are

therefore generally unsaturated and possess negative pore water pressures. Climatic

Material therefore generally unsaturated and possess negative pore water pressures. Climaticchanges (i.e. evaporation and infiltration) and transpiration influence the water content

Material changes (i.e. evaporation and infiltration) and transpiration influence the water content- changes (i.e. evaporation and infiltration) and transpiration influence the water content- changes (i.e. evaporation and infiltration) and transpiration influence the water contentand the negative pore-water pressure of the unsaturated soils, especially those located

- and the negative pore-water pressure of the unsaturated soils, especially those locatedTaylor

changes (i.e. evaporation and infiltration) and transpiration influence the water contentTaylor

changes (i.e. evaporation and infiltration) and transpiration influence the water contentand the negative pore-water pressure of the unsaturated soils, especially those locatedTaylor

and the negative pore-water pressure of the unsaturated soils, especially those locatedclose to the ground surface. As a result, the hydraulic properties, shear strength and

Taylor close to the ground surface. As a result, the hydraulic properties, shear strength andvolume of the soil vary in response to the climatic changes. The traditional practices

Taylor volume of the soil vary in response to the climatic changes. The traditional practicesof soil mechanics have undergone significant changes during the past few decades.

Taylor of soil mechanics have undergone significant changes during the past few decades.Some of these changes are related to increased attention being given to the unsaturated

Taylor Some of these changes are related to increased attention being given to the unsaturatedsoil zone above the groundwater table. The computational capability available to the

Taylor soil zone above the groundwater table. The computational capability available to the& Some of these changes are related to increased attention being given to the unsaturated& Some of these changes are related to increased attention being given to the unsaturatedsoil zone above the groundwater table. The computational capability available to the& soil zone above the groundwater table. The computational capability available to thegeotechnical engineer has strongly influenced the engineer’s ability to address these

& geotechnical engineer has strongly influenced the engineer’s ability to address theseFrancis

geotechnical engineer has strongly influenced the engineer’s ability to address theseFrancis

geotechnical engineer has strongly influenced the engineer’s ability to address thesecomplex problems. The unsaturated soil zone is subjected to a flux-type boundary

Franciscomplex problems. The unsaturated soil zone is subjected to a flux-type boundarycondition for many of the problems faced by geotechnical engineers. Unsaturated soil

Franciscondition for many of the problems faced by geotechnical engineers. Unsaturated soilmechanics has become a necessary tool for analyzing the behaviour of soils in this

Francismechanics has become a necessary tool for analyzing the behaviour of soils in this

FrancisThe behaviour of numerous materials encountered in engineering practice is not

FrancisThe behaviour of numerous materials encountered in engineering practice is not

14 Handbook of tropical residual soils engineering

Evaporation

Fissuresdesaturation

Saturation

Excessiveevaporation

Equilibrium withwater table

At time ofdepositionFolding of

desiccatedsoil

Totalstress

(σ)

Pore-airpressure(ua)

Pore-waterpressure(uw)

Atm

osph

eric

Evapotranspiration

Figure 1.6 Stress distribution during the desiccation of a soil (After Fredlund and Rahardjo, 1993)

soils that have been difficult to consider within the framework of classical soil mechan-ics. Natural surficial deposits of soil have relatively low water content over a large areaof the Earth. Residual soils have been of particular concern in recent years. Once again,the primary factor contributing to their unusual behaviour is their negative pore-waterpressure. Attempts have been made to use design procedures on these soils based onsaturated soil mechanics, with limited success.

Climate plays an important role in whether a soil is saturated or unsaturated.Water is removed from the soil either by evaporation from the ground surface or byevapotranspiration from a vegetative cover (Figure 1.6). These processes produce anupward flux of water out of the soil. On the other hand, rainfall and other formsof precipitation provide a downward flux into the soil. The difference between thesetwo flux conditions on a local scale largely dictates the pore-water pressure conditionsin the soil. A net upward flux produces a gradual drying, cracking and desiccationof the soil mass, whereas a net downward flux eventually saturates a soil mass. Thedepth of the water table is influenced, amongst other things, by the net surface flux.Grasses, trees and other plants growing on the ground surface dry the soil by applyinga tension to the pore-water through evapotranspiration. Most plants are capable ofapplying 1–2 MPa of tension to the pore-water prior to reaching their wilting point.Evapotranspiration also results in the consolidation and desaturation of the soil mass.

Year after year, the deposit is subjected to varying and changing environmentalconditions. These produce changes in pore-water pressure distribution, which in turn

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Saturation

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Saturation

Total

Copyrighted TotalMaterial

stressMaterial

stress(

Material

(σMaterial

σ)Material

)

Stress distribution during the desiccation of a soil (

Material Stress distribution during the desiccation of a soil (

- soils that have been difficult to consider within the framework of classical soil mechan-- soils that have been difficult to consider within the framework of classical soil mechan-Taylor

soils that have been difficult to consider within the framework of classical soil mechan-Taylor

soils that have been difficult to consider within the framework of classical soil mechan-ics. Natural surficial deposits of soil have relatively low water content over a large area

Taylor ics. Natural surficial deposits of soil have relatively low water content over a large areaof the Earth. Residual soils have been of particular concern in recent years. Once again,

Taylor of the Earth. Residual soils have been of particular concern in recent years. Once again,the primary factor contributing to their unusual behaviour is their negative pore-water

Taylor the primary factor contributing to their unusual behaviour is their negative pore-waterpressure. Attempts have been made to use design procedures on these soils based on

Taylor pressure. Attempts have been made to use design procedures on these soils based on& pressure. Attempts have been made to use design procedures on these soils based on& pressure. Attempts have been made to use design procedures on these soils based on

Climate plays an important role in whether a soil is saturated or unsaturated.& Climate plays an important role in whether a soil is saturated or unsaturated.Francis

Climate plays an important role in whether a soil is saturated or unsaturated.Francis

Climate plays an important role in whether a soil is saturated or unsaturated.Water is removed from the soil either by evaporation from the ground surface or by

FrancisWater is removed from the soil either by evaporation from the ground surface or byevapotranspiration from a vegetative cover (Figure 1.6). These processes produce an

Francisevapotranspiration from a vegetative cover (Figure 1.6). These processes produce anupward flux of water out of the soil. On the other hand, rainfall and other forms

Francisupward flux of water out of the soil. On the other hand, rainfall and other forms

Francisof precipitation provide a downward flux into the soil. The difference between these

Francisof precipitation provide a downward flux into the soil. The difference between thesetwo flux conditions on a local scale largely dictates the pore-water pressure conditions

Francistwo flux conditions on a local scale largely dictates the pore-water pressure conditions

Introduction 15

results in shrinkage and swelling of the soil deposit. The pore-water pressure distri-bution with depth can take on a wide variety of shapes as a result of environmentalchanges (Figure 1.6).

Arid and semi-arid areas usually have a deep groundwater table. Soils locatedabove the water table have negative pore-water pressures. The soils are desaturateddue to the excessive evaporation and evapotranspiration. Climatic changes greatlyinfluence the water content of the soil close to the ground surface. Upon wetting, thepore-water pressure increases, tending toward positive values. As a result, changesoccur in the volume and shear strength of the soil, with many soils exhibiting extremeswelling or expansion when wetted. Other soils are known for their significant lossof shear strength upon wetting. Changes in the negative pore-water pressures asso-ciated with heavy rainfall are the cause of numerous slope failures. Reductions inthe bearing capacity and resilient modulus of soils are also associated with increasesin pore-water pressures. These phenomena indicate the important role that negativepore-water pressure plays in controlling the mechanical behaviour of unsaturated soils.

The types of problems of interest in unsaturated soil mechanics are similar to thoseof interest in saturated soil mechanics. Common to all unsaturated soil situations arethe negative pressures in the pore-water. Some of these problems are given below.

Natural slopes subjected to environmental changes

Natural slopes are subjected to a continuously changing environment (Figure 1.7).An engineer may be asked to investigate the present stability of a slope, and predictwhat would happen if the geometry of the slope were changed or if the environmentalconditions should happen to change. Most or all of the potential slip surfaces maylie above the groundwater table. In other words, the potential slip surface may passthrough unsaturated soils with negative pore-water pressures. Typical questions thatmight need to be addressed are (Fredlund and Rahardjo, 1993):

• What effect could changes in the geometry have on the pore pressure conditions?• What changes in pore pressures would result from a prolonged period of

precipitation?• How could reasonable pore pressures be predicted?• Could the location of a potential slip surface change as a result of precipitation?• How significantly would slope stability analysis be affected if negative pore-water

pressures were ignored?• What would be the limit equilibrium factor of safety of the slope as a function of

time?• What lateral deformations might be anticipated as a result of changes in pore

pressures?

Similar questions might be of concern with respect to relatively flat slopes. Surfacesloughing commonly occurs on slopes following prolonged periods of precipitation.These failures have received little attention from an analytical standpoint. One of themain difficulties appears to have been associated with the assessment of pore-waterpressures in the zone above the groundwater table. The slow, gradual, downslope creepof soil is another aspect which has not received much attention in the literature. It hasbeen observed, however, that the movements occur in response to seasonal environment

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of shear strength upon wetting. Changes in the negative pore-water pressures asso-Copyrighted

of shear strength upon wetting. Changes in the negative pore-water pressures asso-ciated with heavy rainfall are the cause of numerous slope failures. Reductions in

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ciated with heavy rainfall are the cause of numerous slope failures. Reductions inthe bearing capacity and resilient modulus of soils are also associated with increases

Copyrighted

the bearing capacity and resilient modulus of soils are also associated with increasesin pore-water pressures. These phenomena indicate the important role that negative

Copyrighted

in pore-water pressures. These phenomena indicate the important role that negativepore-water pressure plays in controlling the mechanical behaviour of unsaturated soils.

Copyrighted

pore-water pressure plays in controlling the mechanical behaviour of unsaturated soils.The types of problems of interest in unsaturated soil mechanics are similar to those

Copyrighted

The types of problems of interest in unsaturated soil mechanics are similar to thoseof interest in saturated soil mechanics. Common to all unsaturated soil situations are

Copyrighted of interest in saturated soil mechanics. Common to all unsaturated soil situations arethe negative pressures in the pore-water. Some of these problems are given below.

Copyrighted the negative pressures in the pore-water. Some of these problems are given below.

Natural slopes subjected to environmental changes

Copyrighted Natural slopes subjected to environmental changesMaterial

Natural slopes subjected to environmental changesMaterial

Natural slopes subjected to environmental changes

Natural slopes are subjected to a continuously changing environment (Figure 1.7).Material

Natural slopes are subjected to a continuously changing environment (Figure 1.7).An engineer may be asked to investigate the present stability of a slope, and predict

Material An engineer may be asked to investigate the present stability of a slope, and predictwhat would happen if the geometry of the slope were changed or if the environmental

Material what would happen if the geometry of the slope were changed or if the environmentalconditions should happen to change. Most or all of the potential slip surfaces may

Material conditions should happen to change. Most or all of the potential slip surfaces maylie above the groundwater table. In other words, the potential slip surface may pass

Material lie above the groundwater table. In other words, the potential slip surface may pass- through unsaturated soils with negative pore-water pressures. Typical questions that- through unsaturated soils with negative pore-water pressures. Typical questions thatTaylor

through unsaturated soils with negative pore-water pressures. Typical questions thatTaylor

through unsaturated soils with negative pore-water pressures. Typical questions thatmight need to be addressed are (Fredlund and Rahardjo, 1993):Taylor

might need to be addressed are (Fredlund and Rahardjo, 1993):Taylor What effect could changes in the geometry have on the pore pressure conditions?

Taylor What effect could changes in the geometry have on the pore pressure conditions?What changes in pore pressures would result from a prolonged period of

Taylor What changes in pore pressures would result from a prolonged period of

& Could the location of a potential slip surface change as a result of precipitation?

& Could the location of a potential slip surface change as a result of precipitation?Francis

Could the location of a potential slip surface change as a result of precipitation?Francis

Could the location of a potential slip surface change as a result of precipitation?How significantly would slope stability analysis be affected if negative pore-water

FrancisHow significantly would slope stability analysis be affected if negative pore-water

FrancisWhat would be the limit equilibrium factor of safety of the slope as a function of

FrancisWhat would be the limit equilibrium factor of safety of the slope as a function of

What lateral deformations might be anticipated as a result of changes in pore

FrancisWhat lateral deformations might be anticipated as a result of changes in pore

16 Handbook of tropical residual soils engineering

Soilstratum 1

Rainfall

Phreatic surface

Soilstratum 2

SlipsurfaceSoil

stratum 3

Figure 1.7 An example of the effect of excavations on a natural slope subjected to environmentalchange (After Fredlund and Rahardjo, 1993)

changes. Wetting and drying are known to be important factors. It would appearthat an understanding of unsaturated soil behaviour is imperative in formulating ananalytical solution to these problems.

Stability of vertical or near-vertical excavations

Vertical or near-vertical excavations are often used for the installation of a founda-tion or a pipeline (Figure 1.8). It is well known that the backslope in a moist siltyor clayey soil will remain as a near-vertical slope for some time before failing. Fail-ure of the backslope is a function of the soil type, the depth of the excavation, thedepth of tension cracks and the amount of precipitation, as well other factors. In theevent that the contractor should leave the excavation open longer than planned, orshould a high precipitation period be encountered, the backslope may fail, causingdamage and possible loss of life. The excavations being referred to are in soils abovethe groundwater table where the pore-water pressures are negative. The excavationof soil also produces a further decrease in the pore-water pressures. This results in anincrease in the shear strength of the soil. With time, there will generally be a grad-ual increase in the pore-water pressures in the backslope, and a corresponding loss instrength. The increase in the pore-water pressure is the primary factor contributing tothe instability of the excavation. Engineers often place responsibility on the contractorfor ensuring backslope stability. Predictions associated with this problem require an

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stratum 2Copyrighted

stratum 2

stratum 3

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stratum 3

Material An example of the effect of excavations on a natural slope subjected to environmental

Material An example of the effect of excavations on a natural slope subjected to environmentalFredlund and Rahardjo, 1993)

Material Fredlund and Rahardjo, 1993)- Taylor

changes. Wetting and drying are known to be important factors. It would appearTaylor

changes. Wetting and drying are known to be important factors. It would appearthat an understanding of unsaturated soil behaviour is imperative in formulating an

Taylor that an understanding of unsaturated soil behaviour is imperative in formulating an

& Vertical or near-vertical excavations are often used for the installation of a founda-& Vertical or near-vertical excavations are often used for the installation of a founda-Francis

Vertical or near-vertical excavations are often used for the installation of a founda-Francis

Vertical or near-vertical excavations are often used for the installation of a founda-tion or a pipeline (Figure 1.8). It is well known that the backslope in a moist silty

Francistion or a pipeline (Figure 1.8). It is well known that the backslope in a moist silty

Francisor clayey soil will remain as a near-vertical slope for some time before failing. Fail-

Francisor clayey soil will remain as a near-vertical slope for some time before failing. Fail-ure of the backslope is a function of the soil type, the depth of the excavation, the

Francisure of the backslope is a function of the soil type, the depth of the excavation, thedepth of tension cracks and the amount of precipitation, as well other factors. In the

Francisdepth of tension cracks and the amount of precipitation, as well other factors. In theevent that the contractor should leave the excavation open longer than planned, or

Francisevent that the contractor should leave the excavation open longer than planned, or

Introduction 17

Tensioncracks

Siltyclay

Negativepore-water pressures

Water table

Potentialslip surface

Figure 1.8 An example of potential instability in a near-vertical excavation during the construction ofa foundation (After Fredlund and Rahardjo, 1993)

understanding of unsaturated soil behaviour. Some relevant questions that might beasked are (Fredlund and Rahardjo, 1993):

• How long will the excavation backslope stand prior to failing?• How could the excavation backslope be modeled analytically, and what would be

the boundary conditions?• What soil parameters are required for the above modeling?• What in-situ measurements could be taken to indicate incipient instability?• Also, could soil suction measurements be of value?• What effect would a ground surface covering (e.g. plastic sheeting) have on the

stability of the backslope?• What would be the effect of temporary bracing, and how much bracing would be

required to ensure stability?

Lateral earth pressures

Figure 1.9 shows two situations where an understanding of lateral earth pressures isnecessary. Some situations might involve lateral pressure against a grade beam placedon piles. Let us assume that in each situation a relatively dry clayey soil has been placedthere and compacted. With time, water may seep into the soil, causing it to expand bothvertically and horizontally. Although these situations may illustrate the developmentof high lateral earth pressures, they are not necessarily good design procedures. Somequestions that might be asked are (Fredlund and Rahardjo, 1993):

• How high might the lateral pressures be against a vertical wall with wetting of thebackfill?

• What are the magnitudes of the active and passive earth pressures for anunsaturated soil?

• Are the lateral pressures related to the ‘swelling pressure’ of the soil?

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Copyrighted

An example of potential instability in a near-vertical excavation during the construction of

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An example of potential instability in a near-vertical excavation during the construction ofa foundation (

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a foundation (After

Copyrighted

Aftera foundation (Aftera foundation (

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a foundation (Aftera foundation (

understanding of unsaturated soil behaviour. Some relevant questions that might be

Copyrighted understanding of unsaturated soil behaviour. Some relevant questions that might beasked are (Fredlund and Rahardjo, 1993):

Copyrighted asked are (Fredlund and Rahardjo, 1993):Material

understanding of unsaturated soil behaviour. Some relevant questions that might beMaterial

understanding of unsaturated soil behaviour. Some relevant questions that might beasked are (Fredlund and Rahardjo, 1993):Material

asked are (Fredlund and Rahardjo, 1993):

How long will the excavation backslope stand prior to failing?

Material How long will the excavation backslope stand prior to failing?How could the excavation backslope be modeled analytically, and what would be

Material How could the excavation backslope be modeled analytically, and what would be

What soil parameters are required for the above modeling?

Material What soil parameters are required for the above modeling?What in-situ measurements could be taken to indicate incipient instability?

Material What in-situ measurements could be taken to indicate incipient instability?- What in-situ measurements could be taken to indicate incipient instability?- What in-situ measurements could be taken to indicate incipient instability?Also, could soil suction measurements be of value?

- Also, could soil suction measurements be of value?Taylor

What in-situ measurements could be taken to indicate incipient instability?Taylor

What in-situ measurements could be taken to indicate incipient instability?Also, could soil suction measurements be of value?Taylor

Also, could soil suction measurements be of value?What effect would a ground surface covering (e.g. plastic sheeting) have on the

Taylor What effect would a ground surface covering (e.g. plastic sheeting) have on the

What would be the effect of temporary bracing, and how much bracing would be

Taylor What would be the effect of temporary bracing, and how much bracing would be

& FrancisFigure 1.9 shows two situations where an understanding of lateral earth pressures is

FrancisFigure 1.9 shows two situations where an understanding of lateral earth pressures isnecessary. Some situations might involve lateral pressure against a grade beam placed

Francisnecessary. Some situations might involve lateral pressure against a grade beam placedon piles. Let us assume that in each situation a relatively dry clayey soil has been placed

Francison piles. Let us assume that in each situation a relatively dry clayey soil has been placedthere and compacted. With time, water may seep into the soil, causing it to expand both

Francisthere and compacted. With time, water may seep into the soil, causing it to expand both

18 Handbook of tropical residual soils engineering

Naturalsilty clay

Natural clay

Drain with sand backfill

Compactedclaybackfill

Housebasementwall

Precipitation and lawn watering

Compactedsiltyclay

Precipitation

(a)

(b)

Figure 1.9 Examples of lateral earth pressures generated subsequent to backfilling with dry soils:(a) lateral earth pressures against a retaining wall as water infiltrates the compacted backfill;(b) lateral earth pressure against a house basement wall (After Fredlund and Rahardjo, 1993)

• Is there a relationship between the ‘swelling pressure’ of a soil and the passiveearth pressure?

• How much lateral movement might be anticipated as a result of the backfillbecoming saturated?

Foundations

The foundations for light structures are generally shallow spread footings (Figure 1.10).The bearing capacity of the underlying (clayey) soils is computed on the basis of theunconfined compressive strength of the soil. Shallow footings can easily be constructedwhen the water table is below the elevation of the footings. In most cases, the watertable is at a considerable depth, and the soil below the footing has a negative pore-water pressure. Undisturbed samples, held intact by negative pore-water pressures,are routinely tested in the laboratory. The assumption is that the pore-water pressureconditions in the field will remain relatively constant with time, and therefore theunconfined compressive strength will also remain essentially unchanged. Based on thisassumption, and on a relatively high design factor of safety, the bearing capacity ofthe soil is computed.

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(a)Copyrighted

(a)Copyrighted

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Copyrighted Natural clay

Copyrighted Natural clay

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Material Drain with sand backfill

Examples of lateral earth pressures generated subsequent to backfilling with dry soils:

Material Examples of lateral earth pressures generated subsequent to backfilling with dry soils:- Examples of lateral earth pressures generated subsequent to backfilling with dry soils:- Examples of lateral earth pressures generated subsequent to backfilling with dry soils:(a) lateral earth pressures against a retaining wall as water infiltrates the compacted backfill;

- (a) lateral earth pressures against a retaining wall as water infiltrates the compacted backfill;Taylor

Examples of lateral earth pressures generated subsequent to backfilling with dry soils:Taylor

Examples of lateral earth pressures generated subsequent to backfilling with dry soils:(a) lateral earth pressures against a retaining wall as water infiltrates the compacted backfill;Taylor

(a) lateral earth pressures against a retaining wall as water infiltrates the compacted backfill;(b) lateral earth pressure against a house basement wall (

Taylor

(b) lateral earth pressure against a house basement wall (

Is there a relationship between the ‘swelling pressure’ of a soil and the passive

Taylor Is there a relationship between the ‘swelling pressure’ of a soil and the passive

How much lateral movement might be anticipated as a result of the backfill

Taylor How much lateral movement might be anticipated as a result of the backfill& How much lateral movement might be anticipated as a result of the backfill& How much lateral movement might be anticipated as a result of the backfillFrancisThe foundations for light structures are generally shallow spread footings (Figure 1.10).

FrancisThe foundations for light structures are generally shallow spread footings (Figure 1.10).The bearing capacity of the underlying (clayey) soils is computed on the basis of the

FrancisThe bearing capacity of the underlying (clayey) soils is computed on the basis of the

Introduction 19

Spread footing

Unsaturatedsilty clay well abovethe groundwater table

Figure 1.10 Illustration of bearing capacity conditions for a light structure placed on soils with negativepore-water pressure (After Fredlund and Rahardjo, 1993)

The above design procedure has involved soils with negative pore-water pressures.It appears that the engineer has been almost oblivious to problems related to the long-term retention of negative pore-water pressure when dealing with bearing capacityproblems. Almost the opposite attitude has been taken towards negative pore-waterpressures when dealing with slope stability problems. That is, the attitude of the engi-neer has generally been that negative pore-water pressures cannot be relied upon tocontribute to the shear strength of the soil on a long-term basis when dealing withslope stability problems. These two, seemingly opposite, attitudes or perceptions giverise to the question, ‘How constant are the negative pore-water pressures with respectto time?’ Other questions related to the design of shallow footings that might be askedare (Fredlund and Rahardjo, 1993):

• What changes in pore-water pressures might occur as a result of sampling soilsfrom above the water table?

• What effect does the in-situ negative pore-water pressure and a reduced degree ofsaturation have on the measured, unconfined compressive strength?

• How should the laboratory results be interpreted?• Would confined compression tests more accurately simulate the strength of an

unsaturated soil for bearing capacity design?• How much loss in strength could occur as a result of watering the lawn surrounding

the building?

The above examples show that there are many practical situations involving unsat-urated soils that require an understanding of the seepage, volume change and shearstrength characteristics. In fact, there is often an interaction between, and a simul-taneous interest in, all three aspects of unsaturated soil mechanics. Typically, a fluxboundary condition produces an unsteady-state saturated/unsaturated flow situation

Copyrighted Illustration of bearing capacity conditions for a light structure placed on soils with negative

Copyrighted Illustration of bearing capacity conditions for a light structure placed on soils with negativepore-water pressure (

Copyrighted pore-water pressure (

Material

The above design procedure has involved soils with negative pore-water pressures.Material

The above design procedure has involved soils with negative pore-water pressures.It appears that the engineer has been almost oblivious to problems related to the long-

Material

It appears that the engineer has been almost oblivious to problems related to the long-term retention of negative pore-water pressure when dealing with bearing capacity

Material term retention of negative pore-water pressure when dealing with bearing capacityproblems. Almost the opposite attitude has been taken towards negative pore-water

Material problems. Almost the opposite attitude has been taken towards negative pore-waterpressures when dealing with slope stability problems. That is, the attitude of the engi-

Material pressures when dealing with slope stability problems. That is, the attitude of the engi-neer has generally been that negative pore-water pressures cannot be relied upon to

Material neer has generally been that negative pore-water pressures cannot be relied upon to- neer has generally been that negative pore-water pressures cannot be relied upon to- neer has generally been that negative pore-water pressures cannot be relied upon tocontribute to the shear strength of the soil on a long-term basis when dealing with

- contribute to the shear strength of the soil on a long-term basis when dealing withTaylor

neer has generally been that negative pore-water pressures cannot be relied upon toTaylor

neer has generally been that negative pore-water pressures cannot be relied upon tocontribute to the shear strength of the soil on a long-term basis when dealing withTaylor

contribute to the shear strength of the soil on a long-term basis when dealing withslope stability problems. These two, seemingly opposite, attitudes or perceptions give

Taylor slope stability problems. These two, seemingly opposite, attitudes or perceptions giverise to the question, ‘How constant are the negative pore-water pressures with respect

Taylor rise to the question, ‘How constant are the negative pore-water pressures with respectto time?’ Other questions related to the design of shallow footings that might be asked

Taylor to time?’ Other questions related to the design of shallow footings that might be asked

& What changes in pore-water pressures might occur as a result of sampling soils& What changes in pore-water pressures might occur as a result of sampling soilsFrancis

What changes in pore-water pressures might occur as a result of sampling soilsFrancis

What changes in pore-water pressures might occur as a result of sampling soils

What effect does the in-situ negative pore-water pressure and a reduced degree of

FrancisWhat effect does the in-situ negative pore-water pressure and a reduced degree ofsaturation have on the measured, unconfined compressive strength?

Francissaturation have on the measured, unconfined compressive strength?

FrancisWould confined compression tests more accurately simulate the strength of an

FrancisWould confined compression tests more accurately simulate the strength of an

20 Handbook of tropical residual soils engineering

which results in a volume change and a change in the shear strength of the soil. Thechange in shear strength is generally translated into a change in the factor of safety.There may also be an interest in quantifying the change of other volume-mass soilproperties (i.e. water content and degree of saturation).

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Bell, F.G. (2000). Engineering Properties of Soils and Rocks. 4th edn, Oxford: Blackwell Science.Bergman, E.F. and McKnight, T.L. (1993). Introduction to Geography. Englewood Cliffs,

New Jersey: Prentice Hall.Bland, W. and Rolls, D. (1998). Weathering. London: Arnold.Blight, G.E. (1985). Residual soils in South Africa, in Brand and Philipson (ed.) Sampling and

Testing of Residual Soils: Technical Committee on Sampling and Testing of Residual soils.International Society for Soil Mechanics and Foundation Engineering, 159–168.

Brand, E.W. and Philipson, H.B. (1985). Review of international practice for the samplingand testing of residual soils, in Brand, E.W. and Philipson, H.B. (eds) Sampling and Testingof Residual soils: A Review of International Practices. Technical Committee on Samplingand Testing of Residual Soils, International Society for Soil Mechanics and FoundationEngineering, 7–22.

Fredlund, D.G. and Rahardjo, H. (1993). Soil Mechanics for Unsaturated Soils. New York:John Wiley & Sons.

Ingersoll, A.P. (1983). The atmosphere. Scientific American, Sept., 114–130.Johnson, R.B. and De Graff, J.V. (1988). Principles of Engineering Geology. New York:

John Wiley.McCarthy, D.F. (1993). Essentials of Soil Mechanics: Basic Geotechnics. Englewood Cliffs,

New Jersey: Regents/Prentice Hall.Press, F. and Siever, R. (1994). Understanding Earth. New York: W. H. Freeman.Public Works Institute Malaysia (IKRAM) (1996). Geoguides 1–5, Tropical weathered in-situ

materials.Rollings, M.P. and Rollings, R.S. (1996). Geotechnical Materials in Construction. McGraw-Hill.Sowers, G.F. (1985). Residual soils in the United States, in Brand and Philipson (eds) Sampling

and Testing of Residual Soils: A Review of International Practices. International Society forSoil Mechanics and Foundation Engineering.

Summerfield, M.A. (1996). Global Geomorphology: An Introduction to the Study of Land-forms. Singapore: Longman.

Terzaghi, K. and Peck, R.B. (1967). Soil Mechanics in Engineering Practice. New York: JohnWiley.

Copyrighted

New Jersey: Prentice Hall.Copyrighted

New Jersey: Prentice Hall.Bland, W. and Rolls, D. (1998).Copyrighted

Bland, W. and Rolls, D. (1998).Blight, G.E. (1985). Residual soils in South Africa, in Brand and Philipson (ed.)

Copyrighted

Blight, G.E. (1985). Residual soils in South Africa, in Brand and Philipson (ed.)Testing of Residual Soils: Technical Committee on Sampling and Testing of Residual soils

Copyrighted

Testing of Residual Soils: Technical Committee on Sampling and Testing of Residual soilsInternational Society for Soil Mechanics and Foundation Engineering, 159–168.

Copyrighted

International Society for Soil Mechanics and Foundation Engineering, 159–168.Brand, E.W. and Philipson, H.B. (1985). Review of international practice for the sampling

Copyrighted

Brand, E.W. and Philipson, H.B. (1985). Review of international practice for the samplingand testing of residual soils, in Brand, E.W. and Philipson, H.B. (eds)

Copyrighted and testing of residual soils, in Brand, E.W. and Philipson, H.B. (eds)of Residual soils: A Review of International Practices

Copyrighted of Residual soils: A Review of International Practicesand Testing of Residual Soils, International Society for Soil Mechanics and Foundation

Copyrighted and Testing of Residual Soils, International Society for Soil Mechanics and Foundation

Fredlund, D.G. and Rahardjo, H. (1993).

Copyrighted Fredlund, D.G. and Rahardjo, H. (1993).Material

Fredlund, D.G. and Rahardjo, H. (1993).Material

Fredlund, D.G. and Rahardjo, H. (1993).

Ingersoll, A.P. (1983). The atmosphere.

Material

Ingersoll, A.P. (1983). The atmosphere. Scientific American

Material

Scientific AmericanJohnson, R.B. and De Graff, J.V. (1988).

Material Johnson, R.B. and De Graff, J.V. (1988). Principles of Engineering Geology

Material Principles of Engineering Geology

Essentials of Soil Mechanics: Basic Geotechnics.

Material Essentials of Soil Mechanics: Basic Geotechnics.

- Understanding Earth- Understanding EarthTaylor

. New York: W. H. Freeman.Taylor

. New York: W. H. Freeman.GeoguidesTaylor

Geoguides

Geotechnical Materials in Construction

Taylor Geotechnical Materials in Construction

Sowers, G.F. (1985). Residual soils in the United States, in Brand and Philipson (eds)

Taylor Sowers, G.F. (1985). Residual soils in the United States, in Brand and Philipson (eds)and Testing of Residual Soils: A Review of International Practices

Taylor and Testing of Residual Soils: A Review of International Practices& . International Society for& . International Society for

Global Geomorphology: An Introduction to the Study of Land-& Global Geomorphology: An Introduction to the Study of Land-Francis

Global Geomorphology: An Introduction to the Study of Land-Francis

Global Geomorphology: An Introduction to the Study of Land-

Soil Mechanics in Engineering Practice

FrancisSoil Mechanics in Engineering Practice. New York: John

Francis. New York: John