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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.
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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.
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