Chapter 2

LITERATURE REVIEW

2.1. INTRODUCTION

Consolidation is one of the different processes to which the soil in the

field is subjected. It is a time dependent volume change process that takes place

during the transference of the external superimposed loads to the soil solids as an

effective stress, with the expulsion of pore water fi-om the soil voids. Lack of

understanding of the mechanisms controlling the consolidation of soils has led to

many settlement failures of structures- both uniform and differential settlement,

founded on compressible soil strata. Consolidation behaviour of soils depends

upon initial state of the soils subjected to external forces. The soil mass

undergoing consolidation in the field may be of very soft; consistency with high

initial water content or may be in a loosely packed state or may be in a

compacted state. Majority of constructional activities such as construction of

embankments, dams, pavements and the like take place on a compacted soil

mass. This suggests the importance of the knowledge of consolidation behaviour

of compacted soils.

This chapter intends to review the state of the art pertaining to the

compaction characteristics of fine-grained soils and the consolidation & the

permeability characteristics of compacted swelling & non-swelling soils. The

scope of the present experimental work arrived at as a consequence of this

detailed literature review will also be stated clearly.

2.2. COMPACTION BEHAVIOUR

For a majority of the activities adopted in the field to achieve soil

compaction, the major input is the results of laboratory compaction tests-standard

or modified Proctor compaction tests. The process of compaction, particularly of

fine-grained soils, seems to be a complex one as the soil may be composed of

both active and relatively inactive clay minerals and of non-clay minerals as well.

The results of compaction tests are normally expressed in the form of dry

density v/s water content relationship (Fig. 2.1). The two important compaction

characteristics are optimum moisture content (CMC) and maximum dry density

(pdmax). The important factors which affect these characteristics are the

compactive effort and the type of soil. For a given soil, higher the compactive

effort, higher will be the value of pdmax and lower will be the value of OMC

(Fig. 2.1).

Fig 2.2 shows the effect of soil type on the compaction characteristics.

Well graded soils will have higher pdmax and lower OMC compared with poorly

graded soils. Coarse-grained soils will have higher Pdmax and lower OMC

compared with fine-grained soils.

C| and Co: Compactive Efforts

Co > C, \ .

a •T3

/ - - ^ ^ ^ - ^ ^ ^ ^ ^ Z A V line

Q / ^ ^ ^ \ \

Ci

Water Content

Fig. 2.1: Relationship between dry density and water content

a u

Q

1. Well graded sand

graded sand

ZAV line

Water Content

Fig. 2.2: Effect of soil type on the compaction characteristics

Many theories exist in the geotechnical engineering literature to explain

the compaction process such as lubrication theory (Proctor, 1933), viscous water

theory (Hogentogler, 1936), Capillary theory (Hilf, 1956), physico-chemical

theory (Lambe, 1960), effective stress theory (Olson, 1963), cluster

characteristics theory (Barden and Sides, 1970; Srinivas murthy et al, 1985) and

soil aggregate theory (Hodek and Lovell, 1979).

Hilf (1986) opined that these theories must be considered tentative as they

were based almost entirely on the state of knowledge at the time of their

proposition. No single theory can satisfactorily explain the compaction process,

which is quite complex involving capillary pressure, pore air pressure, pore water

pressure, osmotic pressure, histeresis, permeability, soil surface characteristics,

concept of effective stress, shear strength and compressibility. The problem

becomes much more complicated by the fact that the fine-grained soils are

composed of different clay minerals in different proportions, whose response to

external input may be quite different from one another.

Even though, many researchers have worked on the compaction of fine­

grained soils, no specific work has been reported on the compaction

characteristics of swelling & non-swelling soils and on their controlling

mechanisms.

2.3. CONSOLIDATION CHARACTERISTICS

2.3.1 General

Preconsolidation stress, compression index, and coefficient of

consolidation are the important consolidation characteristics of fine-grained soils.

Preconsolidation stress is of significance while dealing with over consolidated

soils, as over consolidated and normally consolidated soils exhibit widely varying

compressibility behaviour. Compression index is a parameter which helps in the

settlement calculations while coefficient of consolidation is an usefiil parameter

in analysing the time-rate of consolidation behaviour of fine-grained soils.

2.3.2 Preconsolidation stress

Preconsolidation stress (ap') is one of the consolidation characteristics of

over consolidated soils. It is the maximum consolidation stress to which the soil

mass is subjected in the past, and it represents the stress-history of the soil. The

over consolidation of soil mass can be attributed to many causes such as

erosion/removal of previously existed overburden, desiccation of soil mass,

change in the structure due to aging, changes in the chemical environment of the

soil deposit and the changes in the pore water pressure. Several methods have

been documented in the geotechnical engineering literature for the evaluation of

preconsolidation stress of over consolidated soils. A brief description of each of

these methods is given in the following sections.

2.3.2.1 Casagrande method

Casagrande (1936) suggested a simple graphical construction to

determine preconsolidation stress from the laboratory e-log a' plot (Fig. 2.3). The

procedure is as follows.

Effective Consolidation Stress (a')

Fig. 2.3: Casagrande method of determining preconsolidation stress illustrated (schematic)

e-log a' curve is plotted.

By visual observation, point A is established on the curve at which the

curve has a minimum radius of curvature.

A horizontal line AB is drawn at A.

A tangent AC to the curve is drawn at A.

A line AD is drawn, which is a bisector of the angle BAC.

• The straight hne portion GH of the e-log a' curve is projected back to

intersect the line AD at a point F. The abscissa of point F is the

preconsoUdation stress a p'.

The Casagrande method has been commonly observed to give low values,

and it cannot be applied with confidence when e-log a'curve has a large, gently

curved initial region (Bowles, 1997). Clementino(2005) showed that Casagrande

method is scale dependent also.

2.3.2.2 Burmister Method

The method proposed by Burmister (1942, 1951) to determine the

preconsoUdation stress is as follows (Fig. 2.4).

Pi

'o >

Effective Consolidation Stress (o')

Fig 2.4: Burmister method of determining preconsolidation stress - illustrated (schematic)

Start plotting e-log a' curve simultaneously with the loading.

As soon as the straight line portion of the curve is approached, unload the soil

sample, and reload it once again.

Obtain a characteristic triangle (shown shaded in Fig. 2.4) formed by the

rebound and reloading curves.

• Shift this triangle up on to the first loading curve. Determine its position

between the first loading curve and the straight line portion of e-log a' curve

by trial, giving more weightage to the vertical leg than to the horizontal leg.

• Note down the effective consohdation stress corresponding to the position of

the vertical leg as the preconsoUdation stress, a p'.

Burmister method is a trial and error process, and it has to be carried out

along with the loading process simultaneously.

2.3.2.3 Schmertmann method

Schmertamann (1955) proposed a method of determining

preconsoUdation stress, which also involved a trial and error process (Fig. 2.5).

The procedure is as follows.

eo

'o >

a 2 o 3

•a Pi o

I 'o

>

Op' (assumed)

|).42 eo

J I I I I I I I I I I I I

V

Effective Consolidation Stress (o^^

Fig. 2.5: Schmertmann method of determining preconsolidation stress illustrated (schematic)

Start plotting e-log a' curve simultaneously with the loading.

9

• As soon as the straight line portion of the curve is approached, unload the soil

sample, and reload it once again.

• From the point (eo,ao'), draw a line parallel to the mean slope of the

unloading-reloading curves.

• Select a trial point on this line [i.e. cr p' (assumed as shown in Fig. 2.5)].

• From this point, a line is drawn to intersect the laboratory e-log & curve at

0.42 eo. • Sketch the trial virgin curve (shown dotted in Fig. 2.5).

• Plot the void ratio reduction (Ae) between the trial virgin curve and the

laboratory curve against log a'.

• Repeat the above procedure for different trial values of a p.

• Record the trial value of o p', which gives the most symmetrical variation of

Ae with log a' as the required preconsolidation stress, a p.

In addition to being a trial and error process, Schemertmann method is also a time

consuming and laborious method.

2.3.2.4 Janbu method Janbu (1969) proposed a method for determining the preconsolidation

stress based on constrained modulus (M) v/s. a' plot, where constrained modulus

is the reciprocal of coefficient of volume compressibility( i.e., M = 1/ mv).

According to him, the consolidation stress at which there is a marked drop in the

constrained modulus or the stress beyond which the constrained modulus levels

out represents the required preconsolidation stress (Fig. 2.6).

700f

1

O

a T3 U C •s c o

LEGEND: TEST NO. 2 TEST NO. 12

Ap»(X>NST-

TESTS BY ENGES6AAR tl»S8)

10 '20 30 40 50. 60 70 80 Consolidation stress (p'), t/m^

Fig. 2.6: Janbu method of determining preconsolidation stress - illustrated (Janbu, 1969)

10

2.3.2.5 Pacheco Silva's method

This method is based on empirical constructions done on e-log o' plot

(Clementino, 2005). The method involves the following steps (Fig. 2.7).

eo

'5 >

Effective Consolidation Stress (o')

Fig. 2.7: Pacheo Silva's method of determining preconsolidation stress - illustrated (schematic)

• Plot e-log a' curve.

• Draw a horizontal line AB through the initial void ratio (eo) of the specimen.

• Extend back the straight line portion of the virgin compression curve CD to

intersect the line AB at E.

• Drop a vertical line EF jfrom E to intersect the e-log & curve at F.

• From F, draw a horizontal line FG to intersect the extension of the line DC

atG.

• Record the consolidation stress corresponding to point G as the

preconsoUdation stress, a p'.

The advantage claimed by this method is that the method doesn't give

scope for any personal judgment.

11

2.3.2.6 The method of work

The traditional Casagrande method and Janbu method for determining the

preconsoUdation stress cannot be used satisfactorily for more rounded e-log c'

curves. For such cases, Becker et al (1987) proposed a new method known as

method of work. If Awoed is the incremental work done in a consolidation

experiment, it is determined from eq. 2.1.

AWoed= { CTi+r + Cfi'} {Si+i - Si} (2.1)

where C{+i8c ai' are the effective consolidation stresses at the end of (i+1)' & i

loading increments respectively, and Si+i & Si are the corresponding natural

strains (Fig. 2.8).

o

O

>

1

160

140

120

100

T

a LOADING

4 r <> UNLOADING

• RELOADING POSTYIELO LINE

PflEYIELD LINE

200 400 -̂ 600 800

Vertical effective stress (a'), kPa

1000 1^00

Fig. 2.8: The method of work - illustrated (Becker et al, 1987)

12

• Plot the cumulative work done (SAWoed) v/s a' curve, the value of a'

being the value of effective consolidation stress at the end of relevant

stress increment (CTi+i')(Fig. 2.8).

• The curve can be approximated into two linear relationships. Identify

them and draw them.

• Record the value of a' corresponding to the point of intersection of these

two straight lines as the preconsolidation stress, a p'.

This method involves too much of computation and hence, requires the

help of a computer program. In addition, Li (1989) illustrated that this method

was largely influenced by the scale effect.

2.3.2.7 The log-log method

Jose et al (1989) proposed the log-log method for the determination of

preconsohdation stress, which involved the use of logio e v/s logio a' plot.

Sridharan et al (1991) improved this method by suggesting the use of logio (1+e)

v/s logio a' plot. The method is as follows (Fig. 2.9).

+

Effective Consolidation Stress (o')

Fig. 2.9: The log-log method - illustrated (schematic)

13

•

• Plot logio (1+e) v/s logio a' curve.

• Identify two straight line portions on the curve- one in the pre-yield

region and other in the post-yield region, and draw them.

• Record the consolidation stress corresponding to the point of intersection

of these lines as the preconsolidation stress, ap'.

Sridharan et al (1991) verified this method experimentally with the soils

of known preconsolidation stresses and found that the agreement between the

predicted & the actual values of CT p' to be excellent.

2.3.2.8 The void Index method

Burland (1990) proposed a method, known as the void index method, to

assess the preconsolidation stress for soils for which a p' is not well defined in the

conventional e-log a' plot. This method is as follows.

Determine cioo and Cc from the laboratory tests, where cioo is the void

ratio at a-100 kPa and Cc is the compression index corresponding to

virgin portion of the curve. However, for soils which plot above the A-

line of the plasticity chart, Burland suggested that eioo and Cc could be

estimated from the following empirical correlations.

eioo=0.109+0.679eL-0.089 eL̂ +0.016 CL̂ (2.2)

Cc= 0.256 CL-0.04 (2.3)

where BL is the void ratio at the liquid limit water content of the soil.

Determine the value of void Index (Iv) from the following equation.

Iv = (e-eioo)/Cc (2.4)

Plot Iv v/s logio CT' curve (Fig. 2.10).

Record the consolidation stress corresponding to the break in the bilinear

curve as the preconsolidation stress, Gp.

•

14

X

'o >

•a '» '<''

10 J t I I I. I,IL. -i i I I I, I I I

10̂ , , . „ . , 10̂ Vertical effective stress (o'), kPa

J > I t 11 It 10*

Fig. 2.10: The void index method - illustrated (Burland, 1990)

2.3.2.9 Jacobsen 's Method

Jabcobsen (1992), based on his evaluation of the stress-strain curves from

oedometer tests on Danish over consolidated clays combined with the concepts of

Terzaghi and Casagrande, proposed an estimation of the preconsolidation stress

from eq. 2.5.

cjp' = 2 .5ak ' (2.5)

where Ok is the consolidation stress corresponding to the point of maximum

curvature on the e-log a' curve defined by Casagrande (1936). This method

appears to be very simple. However, the value of CTp' depends upon the

identification of the point of maximum curvature on the e-log a' curve, which

involves personal judgment. In addition, the validity of Jacobsen's method has

not been checked for soils other than Danish clays.

15

2.3.2.10 n - logio o" method

Allam and Robinson (1997) proposed the use of n v/s logio cf'

plot, where n is the porosity of the soil sample corresponding to a', to determine

the value of preconsolidation stress, instead of conventional e-logio cf' plot

(Fig. 2.11). The procedure is as follows.

• Plot n-log 10 cy' curve.

• Identify two linear regions on the curve- one in the initial stretch and

other in the later stretch, and draw them.

• Record the value of consolidation stress corresponding to the point of

intersection of these two straight lines as preconsolidation stress , a^.

o 2 o

Vertical effective stress (a')

Fig. 2.11: n-logio o' method - illustrated (schematic)

Allam and Robinson (1997) validated their method with experiments on

soils of known stress-history and found that the results obtained were in

agreement with those determined by Casagrande method. This method is very

similar to the log-log method by Sridharan et al (1991). However, it is to be

noted that n-logio a' method requires additional calculations to obtain the values

of porosities at different consolidation stresses. 16

Apart from these methods, the literature also documents the bilogarithmic

approach by Onitsuka et al (1995). They suggested the use of logn (1+e) v/s logio

a' plot instead of conventional e-log a' plot. It is to be noted here that this method

is nothing but the log-log method proposed by Sridharan et al {\99\) with the

only difference that the logarithm to base 10 is replaced by natural logarithm.

The review of literature on procedures of determining the

preconsolidation stress indicates that different methods discussed have their own

merits and limitations. It has also been noted that no work has been reported by

the researchers on the preconsolidation stress of compacted soils.

2.3.3 Co-efficient of consolidation

2.3.3.1. General

The coefficient of consolidation (Cy) is an important consolidation

characteristic of a soil required during the time rate of consolidation analysis.

Many theories of consolidation have been developed in the past to model the

complex process of consolidation, such as Terzaghi's one dimensional

consolidation theory (1925), Biot's theory of three dimensional consolidation

(1941), large strain consoUdation theory (Mikasa, 1963; Gibson et al, 1967;

Monte and Krizek, 1976) and the like. However, when the strains resulting from

consolidation process are very small, then Terzaghi's one dimensional

consolidation theory itself can be used for the time rate of consolidation analysis.

Quite a good number of methods are available for the determination of Cy

from the laboratory one dimensional consolidation test data. Most of these

methods are based on Terzaghi's one dimensional consolidation theory. In all

these methods, some characteristic features of the theoretical U-T relationship are

identified on the experimental 5-t relationship, which in turn can be used to locate

some salient points on the experimental curve.

Following is the list of different methods of determining Cv from the

laboratory one dimensional consolidation test data.

• Logarithm of time fitting method (Cassagrande and Fadam, 1940)

• Square root of time fitting method (Taylor, 1942)

• Successive approximation method (Naylor and Doran, 1948)

• Steepest slope method (Su, 1958)

17

Scott's method (Scott, 1961)

Numerical method (Madhav, 1964)

Inflection Point Method (Cour, 1971)

Best fit method (Rao, 1975)

Method by Sivaram and Swamee (1977)

Velocity method (Parkin, 1978,1981)

Observational procedure (Asoaka, 1978)

Method by Magnan and Deroy [as referred by Parkin and Lun (1984)].

Rectangular hyperbola method (Sridharan and Sreepada Rao, 1981;

Sridharan and Prakash, 1985; Sridharan e? a/, 1987)

Log (6/t) v/s log t method (Pandian et al, 1992)

5 v/s t/6 method (Sridharan and Prakash, 1993)

Improved velocity method (Pandian et al, 1994)

Logio (H^/t) v/s U method (Sridharan et al, 1995)

Two point method (Prasad and Rao, 1995)

Early stage of log t plot method (Robinson and AUam, 1996)

Improved Vt method (Tewatia and Venkatachalam, 1997)

Log5-log t method (Sridharan and Prakash, 1997)

Tewatia's method (Tewatia, 1998)

Non-graphical matching method (Robinson and AUam, 1998)

One point method (Sridharan and Prakash, 1998)

Robinson's Method (Robinson, 1999)

Linear Segment of Vt curve method (Feng and Lee, 2001)

Least squares method (Chan, 2003).

2.3.3.2 Factors affecting coefficient of consolidation

The coefficient of consolidation has been found to decrease with an

increase in the degree of sample disturbance (Chang, 2001).

Limited experimental data are available in the geotechnical engineering

literature illustrating the variation of Cy with consolidation stress. Terzaghi and

Peck (1967) observed fairly constant Cv values over a wide range of consolidation

stress. Leonards and Ramiah (1959) observed that the values of Cy for remoulded

18

residual clay increased with consolidation stress up to a certain value and

decreased with further increase in the consolidation stress. They also noted that

the values of Cv for the remoulded glacial silty clay continued to increase with

consolidation stress.

Experimental evidences from the studies on virgin consolidation

behaviour are available in the geotechnical engineering literature to show that the

kaolinitic and montmorillonitic soils exhibit contradictory trends in the variation

of Cv with consolidation stress (Table 2.1)

Table 2.1: Variation of Cy with o' and clay mineral type

Soil type Dominant clay

mineral

Liquid limit:

%

Plasticity index: %

Variation of Cv with Reference

Bentonite Montmorillonite 118.0 72.0 Decrease Samarasinghe etal il9S2) Kaolinite Kaolinite - - Increase

Samarasinghe etal il9S2)

Kaolinite Kaolinite 49.0 11.8 Increase Sridharan et

al(1994)

Coarse kaolinite Kaolinite 48.0 12.4 Increase

Prakash (1997)

Fine kaolinite Kaolinite 46.8 17.4 Increase Prakash (1997) Black cotton

soil-2 Montmorillonite 100.8 48.9 Decrease

Prakash (1997)

Bentonite Montmorillonite 393.4 343.3 Decrease

Prakash (1997)

Kaolinite Kaolinite 53.0 21.0 Increase Robinson and AUam (1998) Montmorillonite Montmorillonite 321.0 263.0 Decrease Robinson and AUam (1998)

The study of this data suggests that Cv value decreases with increase in

consolidation stress for montmorillonitic soils and increases with increase in

consolidation stress for kaolinitic soils.

Robinson and AUam (1998) have shown that the response of Cy to

increase in consolidation stress on clays undergoing virgin compression is

governed by mechanical or physio-chemical factors depending upon the

dominant clay mineral composing the soil.

The review of the literature on coefficient of consohdation of soils

indicates that almost no study has been reported on the coefficient of

consolidation of compacted swelling & non-swelling soils.

19

2.3.4 Compression index

The compression index (Q) and coefficient of volume compressibility

(mv) represent important soil parameters required in the settlement calculations.

The compression index is normally considered as the slope of the virgin

compression portion of the e v/s log a' plot, approximating the virgin

compression portion of the curve as a straight line. Many studies were reported

relating compression index of soils with the liquid limit related factors

(Skempton, 1944; Nagaraj and Murthy, 1983, 1986; Nagaraj et al, 1993) and with

the void index (Burland, 1990). Several researchers have studied the

compression index as a derived soil property fi-om one or more easily

determinable basic soil index properties (Koppula, 1981; Carrier III, 1985,

Sridharan and Nagaraj, 2000).

Cerato and Lutengger (2004) found that the clay minerology might

influence the degree to which the initial water content would affect the

compression curve of the remoulded soil.

AdduUah et al (1997) found that the virgin compression index was a

constant for compacted soils tested by them and related it with the initial dry

density of the soil.

Many studies have been reported illustrating the compression index as a

variable with the effective consolidation stress (Sridharan and Gurtug, 2005).

They reported an increase in the value of the slope of the virgin compression

curve for the soils tested by them compacted to maximum dry density at optimum

moisture content.

Sridharan and Prakash (2001) noticed contradictory trends in the variation

of the slope of the virgin compression curve for soils with different clay

minerological composition.

No study has been reported in the geotechnical engineering literature on

the variation of compression index of compacted soils with the effective

consolidation stress, considering the soil clay minerological composition and also

on the variation of compression index along the compaction curve.

20

2.3.5 Permeability of compacted soils

Penneability is one of the three important engineering properties of fine­

grained soils. Permeability of compacted soils becomes all the more important

firom the view point of performance of various geotechnical engineering

structures such as earth embankments, earth dams and soil subgrades for

pavements.

Way back in 1856, Darcy demonstrated through his experiments on filter

sand that the rate of flow (Q) was proportional to the hydraulic gradient (i)

(Terzaghi, 1925).

i.e., Q = k i A (2.6)

or v = Q/A =ki (2.7)

where A - total cross section area of the soil mass normal to the flow direction.

V = average velocity of flow and

k = the coefficient of permeability.

The two standard methods normally used to determine the value of

coefficient of penneability are constant head method (used for more permeable

soils) and variable head method (used for less permeable soils). These methods

assume that the Darcy's law is valid.

Many researchers validated the Darcy's law through their experimental

works (Terzaghi, 1925; Maceay, 1942; Michaels and Lin, 1954; Low, 1960;

Gairon and Swarzendruber, 1975; Tavenas et al, 1983; Prakash, 1997; to name a

few). However, the geotechnical engineering literature also documents studies

indicating non-Darcian flow behaviour (Lutz and Kemper, 1959; Hansbo, 1960;

2003; Gayron and Swartzendruber, 1975; Foreman and Daniel, 1984; Acar et al,

1985; Prakash, 1997; Kodikara and Rahman, 2001; to name a few). Many

experimental results have been reported in geotechnical engineering literature

indicating the presence of a threshold gradient (ic) above which the rate of flow

v/s hydraulic gradient relationship is linear (Lutz and Kemper, 1959; Hansbo,

1960; Swartzendruber, 1961; Li, 1963; MiUer and Low, 1963; Gayron and

Swartzendruber, 1975; Law and Lee, 1981; Olsen, 1985; Doubin and Moulin,

1986; to name a few). A detailed review of literature pertaining to non-Darcian

21

flow through fine- grained soils up to 1973 has been given in Basak and Madhav

(1973).

Many researchers have studied this important topic of permeability of

fine-grained soils with different aims.

Mesri and Olson (1971) studied the mechanism controlling the

permeability of clays. Many contributions were documented on the stress-state

permeability relationship and generalisation of permeability behaviour (Nagaraj

and Jayadeva, 1981; Nagaraj and Srinivasa Murthy, 1983, 1986a; Srinivasa

Murthy et al, 1988; Nagaraj et al, 1993). Many researchers observed a linear

variation in e-log k plot (Taylor, 1948; Lambe and Whitman 1969; Altabba et al,

1987; Nash era/, 1992).

Sridharan and Prakash (2001) have shown that the coefficient of

permeability of fine- grained soils is a fiinction of stress-history in addition to

void ratio and soil type.

Literature indicating non-linear e-log k relationship for fine-grained soils

is also available (Mesri and Olsen, 1971; Prakash, 1997)

When compared with the documented literature on permeability of fine­

grained soils related with various factors, the studies on permeability of

compacted soils are very limited. It has been observed that coefficient of

permeability decreases fi-om maximum value on the dry side of optimum of

standard Proctor compaction curve to reach a minimum at or slightly beyond

optimum moisture content. Mitchell et al (1965) attributed this tendency to the

features such as complex interaction between soil & water, soil type, compactive

effort, changes in structure of soils due to compaction, non-uniform saturation

and shear strain during compaction. Mitchell et al, (1965) also discussed the

effect of soil structures on the permeability of compacted soils. They showed

that kneading compaction resulted in lower permeabilities than static compaction.

Benson and Trast (1995) developed regression equation to estimate the

coefficient of permeability of compacted soils using initial saturation, compactive

effort, plasticity index and clay content. Watabe et al., (2000) concluded fi:om

their studies on permeability of glacial till that the degree of saturation achieved

during compaction would greatly affect the coefficient of permeability.

22

From the study of the literature on permeabiHty of compacted soils, it is

observed that no study has been reported on the validity of Darcy's law for the

flow^ through compacted swelling and non-swelling soils.

2.4 SCOPE OF THE WORK

As a consequence of the review of the pertinent literature, scope of the

present experimental work has been arrived at, and it is listed as indicated below.

• The present work intends to study the compaction characteristics of swelling

and non-swelling soils of the same type which is represented through their

liquid limits.

• The present experimental work intends to determine the preconsolidation

stresses of compacted swelling and non-swelling soils along their compaction

curves. In view of its inbuilt merits and established validity with soils of

known stress-history, the log-log method proposed by Sridharan et al (1991)

is adopted to determine the value of preconsolidation stress of compacted

soils in this investigation.

• The present experimental work intends to study the variation of co-efficient of

consolidation of compacted swelling and non-swelling soils. Due to its

simplicity and strong theoretical basis, one point method (Sridharan and

Prakash, 1998), is adopted in the present experimental investigation to

calculate the coefficient of consolidation of soils from one dimensional

consolidation test data.

• The present experimental work intends to study the variation of the

compression index of compacted swelling and non-swelling soils with

effective consolidation stress.

• The present experimental work intends to check the validity of Darcy's law

for the flow through compacted swelling and non-swelling fine-grained soils

and also to study the permeability behavior of compacted swelling and non-

swelling fine-grained soils.

23

2.5 SUMMARY

In view of the great significance attached to the compaction and

consoHdation characteristics of compacted fine-grained soils in the field of

geotechnical engineering, the present experimental work has been taken up. This

chapter presented a brief review of the literature on compaction and consolidation

behavior of fine-grained soils. Guided by the observations made during this

literature review, scope of the present experimental work has been identified and

stated clearly.

24