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International Journal of Advanced Research in Engineering and Technology (IJARET) Volume 11, Issue 10, October 2020, pp. 903-918, Article ID: IJARET_11_10_090
Available online at
http://www.iaeme.com/IJARET/issues.asp?JType=IJARET&VType=11&IType=10
ISSN Print: 0976-6480 and ISSN Online: 0976-6499
DOI: 10.34218/IJARET.11.10.2020.090
© IAEME Publication Scopus Indexed
A COMPUTATIONAL TECHNIQUE FOR
ASSESSING THE COMPRESSION PATHS OF
RESIDUAL SOILS
Y. Venkata Subba Reddy
Research Scholar, Department of Civil Engineering, S.V. University, Tirupati, AP, India
K. Nagendra Prasad
Professor of Civil Engineering, Department of Civil Engineering,
S.V. University, Tirupati, AP, India
ABSTRACT
Of the civil engineering construction materials, soil is distinctive being a geologic
material, most often engineered, as it exists, unlike other processed or manufactured
materials like concrete or steel. Therefore, it becomes essential to characterize the soil
appropriately based on factual data available at discrete locations. The discrete
locations are the places where samples are extracted and in-situ tests are performed,
these locations are chosen based on possible variations in soil conditions in the
proposed area of construction of a civil engineering structure. Soil conditions between
such discrete locations can be deduced by scientific principles. An attempt has been
made in the present investigation to propose a computational technique based on
phenomenological observation made on experimental findings on ten different soils
extracted from different depths form a residual soil deposit in Tirupati region. The soil
samples show inherent variation in basic characteristics in terms of grain size and
plasticity characteristics. The soils are predominantly Clayey with silt, sand in
significant proportions. These soils are typical of kind encountered in practice. The
compression paths of natural soils are determined and the these paths are shown vis-à-
vis the compression paths of remolded soils compressed from their equivalent liquid
limit states , free from stress , time and environmental effects in order to ascertain the
relative positioning so as to understand the states of compression paths of natural soils
. The analysis of test results indicate that the compression paths vary from the
compression paths of natural soils and the paths follow a consistent mathematical
pattern when normalized with respective initial void ratios with stress. These
observations form basis to propose a simple computational technique to predict the
compressibility behaviour of natural residual soils. The mathematical form observed is
applied to the data published in literature to bring out the applicability of the
phenomenological model.
Y. Venkata Subba Reddy and K. Nagendra Prasad
http://www.iaeme.com/IJARET/index.asp 904 [email protected]
Keywords: Compression Paths, Residual Soils, Phenomenological Approach,
Assessment & Applicability.
Cite this Article: Y. Venkata Subba Reddy and K. Nagendra Prasad, A Computational
Technique for Assessing the Compression Paths of Residual Soils, International
Journal of Advanced Research in Engineering and Technology, 11(10), 2020, pp. 903-
918
http://www.iaeme.com/IJARET/issues.asp?JType=IJARET&VType=11&IType=10
1. INTRODUCTION
The properties of residual soils have received increasing attention from geotechnical engineers
in recent years. In particular, the extent to which conventional soil mechanics concepts are
applicable to residual soils have been addressed by a number of workers in this field. There
appears to be a widely held view that the direct applications of such concepts to residual soils
is likely to pave way for misleading conclusions (Rao and Nagendra Prasad,2016)
The occurrence and distribution of soils in nature is such that, the various type of soil can
be found together. Most of the engineering design methods and parameters of structures on soil
have been developed for ideal soils such as pure sands or pure clays; the reality is that these
ideal soils are rarely found in nature. In a sand-clay mixture, it is quite difficult to establish the
characteristics of the soil since it possesses both the properties of sand and clay (Akayuli et al,
2013)
1.1. Geo-Material Spectrum
Tropical soils are found in tropical regions between tropic of Cancer and the tropic of Capricorn
enclosed between 231
2 0North and 23
1
2 0South of the equator. In these regions evaporation is
more intense compared to precipitation. The soils are residual having been born and deposited
at the place of formation. The characteristic feature of these soils is that the highly weathered
soils are found at shallow depths followed by weathered rock, disintegrated rock and hard rock
at greater depths (Nagendra Prasad et al, 2013).
The in-situ soil formations might arise due to sedimentation or may be non-sedimentary
residual deposits in origin. Although soils, primarily, are particulate media, the stresses to which
they are subjected to, the environment in which the deposits are formed and the time, in the
geological time scale, that has elapsed, have all been recognized as potential factors to impart
their effects to the in-situ soil systems encountered. It is very well known that the equilibrium
state of the in-situ deposits is the resultant effects of stress, time and environment. Particularly
soils in the Southern Indian region are residual in nature (those derived by in-situ weathering
of rocks). In residual soils the particles and their arrangement would have evolved progressively
as a consequence of physical and chemical weathering. Although the geological study of the
formation and structure of in-situ residual soils is well advanced, the simple and rapid methods
to analyze and assess the engineering properties of these soils have not received the same level
of attention. This is in contrast to the situation while sedimentary soil deposits are encountered.
Quite often cementation in rock would be left behind due to varied degrees of weathering
(Nagendra Prasad et al, 2007).
Residual soils are formed by the in situ physical and chemical weathering of underlying
rock, while sedimentary soils are formed by a process of erosion and transportation followed
by deposition and consolidation under their own weight. In addition, the latter may undergo
further alteration after deposition due to processes such as secondary consolidation, leaching
and thixotropic effects (Bjerrum, 1967). Natural soils consist of soil constituents varying in size
from colloidal to coarse sand. The available methods to predict the compressibility of soils with
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liquid limit as a parameter do not account for coarse particles. The modified liquid limit concept
proposed by Srinivasa Murthy et.al., (1987), wLM
= wL
(F/100), where, wLM
= Modified liquid
limit of the soil ,F = Percent fine passing 425 μm sieve , wL
= Liquid limit of soil on fraction
finer than 425 μm has been used to predict intrinsic compression lines ( Srinviasamurthy
etal,1987). In the present investigation the possibility of analysis and exercising engineering
judgment to arrive at engineering parameters applicable for the tropical residual soils is
examined.
2. BACKGROUND INFORMATION
The various formation factors responsible for differences in behavior between residual soils and
sedimentary (transported) soils are described. The extent to which classical soil mechanics
concepts derived from the study of sedimentary soils are applicable to residual soils is examined
and discussed (Wesley, 1990). It is shown that residual soils can be wrongly evaluated as
problem soils simply because some aspects of their behavior do not conform to that of
sedimentary soil. The relative importance of composition and structure in influencing residual
soil behavior is examined by carrying out consolidation and triaxial tests on three residual soils,
namely, silt, a tropical red clay, and an and andosol (volcanic ash soil). The need for an
empirical or theoretical framework applicable to residual soils, in place of the stress history
framework used with sedimentary soils, is discussed.
In a tropical region, residual soil layers can be very thick, sometimes extending to hundreds
of meters before reaching un-weathered rock. Unlike the more familiar transported sediment
soil, the engineering properties and behaviour of tropical residual soils may vary widely from
place to place depending upon the rock of origin and the local climate during their formation;
and hence are more difficult to predict and model mathematically. Despite their abundance and
significance, our knowledge and understanding of these soils is not as extensive as that of
transported sediment soil (Huat et al. 2013). However, with respect to residual soil, both its
interaction mechanism and its failure behaviour in soil composites are not well understood due
to limited study (Mofiz et al. 2010). Tropical soils appear in large regions of the world and have
been less studied than soils from temperate climates, particularly with respect to critical state
and limit state conditions. Most geological materials are structured in nature and this natural
structure influences the behavior of tropical soils ( Nagendra Prasad and Sulochana,2013)..
Structural features affecting soil behavior include soil cementation and soil fabric. Sarma et al.
(2008) observed that the consolidation properties of soils indicate an insight on the
compressibility behaviour of soils with associated expulsion of water. However, determination
of such properties involves considerable time, cost and rigorous testing process. Further, natural
state of partial saturation and soil-moisture is not simulated in the standard consolidation
procedures. The sampling technique is also not specific for the Oedometer tests and sampling
disturbance influences the results considerably. As such, modified methodologies of Odometer
test for field simulation as well as simple correlations of the consolidation parameters with
fundamental properties are always preferred by practicing engineers.
Of the Civil Engineering construction materials, soil is unique being a natural material, most
often engineered, as it exists, unlike other processed or manufactured material like concrete or
steel. Therefore it becomes necessary to characterize the soil appropriately based on factual
data available at discrete locations. The discrete locations are the places where samples are
extracted and in-situ tests are performed, these locations are chosen based on possible variations
in soil conditions in the proposed area of construction of a civil engineering structure. Soil
conditions between such discrete locations can be deduced by scientific principles (Rao and
Nagendra Prasad, 2016)
Y. Venkata Subba Reddy and K. Nagendra Prasad
http://www.iaeme.com/IJARET/index.asp 906 [email protected]
The occurrence and distribution of soils in nature varies from location to location. The type
of soil depends on the rock type, its mineral constituents and the climatic regime of the area.
Soils are used as construction materials or the civil engineering structures are founded in or on
the surface of the earth. Geotechnical properties of soils influence the stability of civil
engineering structures. Most of the geotechnical properties of soils influence to each other. In
this paper, different geotechnical properties of soils such as specific gravity, density index,
consistency limits, particle size analysis, compaction, consolidation, permeability and shear
strength and their interactions and applications for the purpose of civil engineering structures
have been discussed ( Roy and Bhalla,2017).
Compressibility behavior of soil is an important parameter that implies the change in
volume under applied stress, on other words; it is the relationship between void ratio and
effective stress. Depending on the type of soil and their origin, the compressibility behavior
varies over a wide range. Researchers presented numerous void ratio-effective stress
relationships consist of different sets of equations which produce a good fit with their
consolidation test data. These sets of equations for different types of soils become complex for
understanding their consolidation behavior using a specific model (Ahmed Syed Iftekhar
& Siddiqua Sumi, 2016). Wesley (1990) reported that the observed pre-consolidation pressures
in residual soils are frequently apparent or pseudo pre-consolidation pressures.
Study of field situations, analysis and design with the incorporation of appropriate material
parameters and finally execution are different chain of events in the practice of geotechnical
engineering. The inherent nature and diversity of geological processes involved in the soil
formation stage itself are responsible for a wide variability in the in-situ state of the soil. Only
a minute fraction of soil can be sampled and tested because of practical and economical
constraints. for example, even if the spacing of boreholes id 10m and 50mm diameter sample
is tested every second meter , only one-millionth of the total volume would have been explored
. In contrast to many other branches of engineering, where one would normally specify the
requirements of the materials used, geotechnical engineer usually has to adjust his design to
accommodate the prevailing properties of the in-situ soils. Hence innovative approaches which
are rational and simple , practical problems can be tackled satisfactorily and economically , if
the soil variability in terms of soil parameters due to erratic conditions can be realistically
arrived at. The need for such approaches by which experimental findings can be synthesized to
establish new , meaningful and simple approaches in holistic manner for analysis and
assessment of soil behaviour as rapidly as possible is obvious.
3. SCOPE OF THE INVESTIGATION
The present investigation has been taken up to propose possible computational technique in
order to assess the compressibility behaviour of in-situ soils. An attempt has also been made to
find out relative positioning of the compression paths of in-situ soils and remolded soils. The
interpretation based on analysis of the data provides a framework to understand the
compressibility characteristics in a unified and coherent manner. The mathematical form
observed is applied to the data published in literature to bring out the applicability of the method
proposed.
4. MATERIALS AND METHODS
The experimental investigation considers soil samples from five different locations of Test Pits
1-5, of Tirupati Region from two different depths at each location. These samples were brought
to laboratory taking care to see that the soils remain fairly undisturbed and intact. The depths
range from 1.40m to 3.90m which depths correspond to usual foundation depths adopted in
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these soils depending on the type of structure. The soils are designated as Soil A, Soil B, Soil
C, Soil D, Soil E, Soil F, Soil G, Soil H, and Soil I for facility of presentation.
4.1. Basic characteristics
The soils are classified predominantly as Clayey Sand (SC) with two of ten samples as Clay
with High Compressibility (CH) as per Indian Standard Classification, IS: 1498-1970. The fine
fraction ranges from 14-70% with average fine fraction being 40%. The Liquid Limit values
range from 34% to 85% with an average value of 55% and the Plasticity Index ranges from
18% to 60% with an average value of 36%. Thus the fine fraction is quite significant and is
active. The properties represent inherent variability. The soils are of this type are typical of the
soils encountered in the region. The soils tested cover wide spectrum of soil variety and the
experimental results on these soils provide basis for analyzing and predicting the soil behaviour
as any soil found locally would fall into one of these categories. The soils are brought to the
laboratory for further processing. The soil samples were air dried and sieved through 20mm
sieve and the fraction passing through the 20mm sieve has been used for determining the index
properties.
4.2. Compressibility Characteristics
The compression paths of undisturbed soil samples from their in-situ state and of remolded soil
samples from slurry state were determined to analyze the relative positioning of these paths
.The compression paths of remolded soils has been determined by mixing the soils with water
content corresponding to 1.15times higher than their respective modified liquid limit values.
Modified liquid limit (Venkata Subba Reddy and Nagendra Prasad, 2020) is calculated by
multiplying the liquid limit values determined for fractions passing through 425 micron sieve
sizes with percent finer than 425 micron. The residual soils are generally found to exist with
composition comprising of sand, silt and clay fractions. Therefore, it is logical to adopt the
modified liquid concept so that when soils are mixed with this order of moisture content, the
mixture forms uniform consistency and when compressed from this order of moisture, the
samples would be completely under remolded state and would be free from stress history, time
and environmental effects. An experimental investigation is taken up on field soil samples
obtained from 10 different depths at different locations from Tirupati surroundings. Tests are
conducted to obtain basic properties of soils apart from one dimensional consolidation test in
oedometer.
All tests were performed as per bureau of Indian Standard Specifications as mentioned in
the Table 1.
Table 1 Tests Conducted
Test Bureau of Indian Standard Specification
Grain size Distribution IS 2720-4:1985
Liquid Limit IS 2720-5:1985
Plastic Limit
Free Swell Index IS 2720-40:1985
In-situ density IS 2720-29:1985
Natural moisture content IS 2720-18:1985
One dimensional consolidation test IS 2720-15:1986
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5. ANALYSES OF TEST RESULTS
The test results are presented in Table 2. It may be observed that the percentage passing from
425 micron sieve size ranges from 82%. This turns out that the liquid limit determined for the
fractions passing through 425 micron may not represent the value for entire fraction and it is
logical to determine the modified liquid limit by concomitantly with the fine fraction. The grain
size distribution diagrams are shown in Figures 1-2 indicate that the distribution is scattered
reflecting the inherent variation though the soils are grouped under nearly same classification
as per Bureau of Indian Standard Specification IS: 1498.The inherent nature and diversity of
geological processes involved in the soil formation stage itself are responsible for a wide
variability in the in-situ state of soil.
Void ratios corresponding to modified liquid limit vary from 0.31 to 1.391 representing
once again wide range of values. The compression paths of the soils are presented in Figure 3.
It may be seen from the figure that the compression paths are linear. The paths are spatially
spread out, with the position of each path being in the order of the liquid limit water content of
the soil. Figure 4 represents the plots of the same paths normalized with their respective void
ratios at modified liquid limit eml. All normalized paths fall within a narrow band and can be
fitted with a linear equation, within the working stress range up to 800kPA, in the form given
by:
v
mle
eln18.0424.1
1
Or
v
mle
e10log414.0424.1
2
The generalized equation is of the same form as given by Nagaraj and Srinivasamurhty,
1986 , but with considerable difference in values of constants.
v
le
e10log234.0122.1
3
The reasons are attributed to the fact that the equation 1 or 2 is developed based on modified
liquid limit concept which is more suited to tropical soils owing to presence of significant coarse
fraction. Burland (1990) proposed void index parameter to generalize the compression path of
remolded soils.
In any investigation, the undisturbed and representative samples at different depths are
available. The representative samples (remolded) are usually used to determine the physical
properties of soils. From the sampled depth data, the overburden pressure can be assessed.
Having a reference state- stress path of the reconstituted soil in relation to which analysis
appears to be the only possibility since the time and structural effects are subdued in the state
of natural deposit. The reference path is independent of the over burden pressure and hence
permits to classify the state of in-situ soil. This is similar to examining the compaction curve
any soil of different degrees of saturation in relation to Zero Air Voids Line.
The compression paths of residual soils are presented in Figures 5-9. The compression
behaviour is characterized by initially rigid response and with noticeable change in void ration
at later stages of loading. Most geo-materials found in tropical residual deposits are structured
in nature and this natural structure affects the behavior of tropical soils. Structural features
affecting soil behavior include soil cementation and soil fabric and stress history. The
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cementation effects cause rigid response initially until the applied load reaches a value causing
de-structuring.
A closer examination of compression paths of undisturbed soil samples and in relation to
their respective remolded paths presents contrasting picture. For samples A-D (Figures 5-6),
the compression paths of in-situ soils are found to be placed on right hand side. As per the state
boundary surface concept (Atkinson and Bransby, 1978), no state of sample exists on right hand
side of Compression paths of remolded /normally consolidated state. The placement of
compression curves on Right Hand Side of Normal compression Line of remolded state
therefore indicates that the soils have additional component of resistance possibly due to
cementation bonds acquired by the structure either due to leaching of salts or due to wetting
and drying cycles. On the other hand the compression paths for the soils E-I (Figures 7-9), the
compression paths are found to exist on left hand side of the remolded compression lines. This
turns out that soils at these locations are in over consolidated state. The compression paths show
rigid response, possibly due to interlocking effects on account of over consolidation and the
compression paths tend to fall in line with remolded compression paths after the stress level
reaches their respective remolded states. It is in conformity with the observation made by
Wesley, 1990) that residual soils can be wrongly evaluated as problem soils simply because
some aspects of their behavior do not conform to that of sedimentary soil. The relative
importance of composition and structure and previous stress effects in influencing residual soil
behavior need to be examined by carrying out consolidation tests on intact and remolded soils
to find out relative influence of these effects. However, it may be noticed that the response of
the in-situ soils is totally different from normally consolidated soil behaviour and the
positioning of the compressibility behviour deepens on cementation or stress effects or both.
The deformations are smaller within the stress range normally applied to soils
The response of the undisturbed soils for monotonous loading in consolidometer is found
to be similar for all the soils tested (Figure 10). The compression curves are placed according
as their initial states represented by respective void ratios with some overlapping at higher stress
levels , possibly due to de-structuring effects . An attempt has been made to normalize the
compression behaviour with respect to their respective intial void ratios, as shown in Figure 11.
It may be noticed that the compression paths fall over a narrow band given by the following
mathematical expression
969.09963.0 20004.0
0
Ree
ev
4
This indicates that the compression paths take exponential form on normalized scale of void
ratios with their respective initial states represented by in-situ void ratios with stress. This is
referred to as phenomenological model hereafter.
6. APPLICABILITY OF THE PHENOMENOLOGICAL MODEL
Yahia et al (2006) considered residual soils from six different depths and are classified as sandy
clayey silt with medium to high plasticity. The Atterberg limits plot just above or below the A-
line in the plasticity chart (Figure 3), indicating that the soil can have dual symbol (i.e. MH-
CH).The average percentage of silt-clay size is above 60% and that of sand is below 40% with
no gravel. The natural water content is generally close to the plastic limit. The variation in water
content and hence the degree of saturation are reported to be due to local factors such as surface
drainage and presence of clay seams. The variation in amount of clay also produces the variation
in Atterberg limits.
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Consolidation tests were performed on natural undisturbed samples which were existing in
the field in partially saturated state. The samples were saturated in the lab typical consolidation
curves are presented (Yahia et al ,2006). The curves presented are almost identical and the only
slight difference is due to the small differences in initial void ratio and water content. The curves
are considered typical for this type of soils. The soil appears to be over consolidated mainly due
to the weathering action and to less extent to the reduction in stress. Wesley (1990) reported
that the observed pre-consolidation pressures in residual soils are frequently apparent or pseudo
pre-consolidation pressures.
The phenomenological model observed as per equation 4 is applied to these compression
paths and the typical predicted paths are shown in relation to the observed compression paths
as shown in Figures 12-17. It may be observed that the predicted compression paths are agreeing
quite well with the experimental paths. The data of another residual clay (Wesley, 2009) called
Allophane clay of Indonesia is also considered for predicting the compression path by the
Model proposed. The predicted compression paths in relation to experimental observations are
presented in Figure 18. It may be noted that the predicted path matches very well with the
experimental path. This testifies the applicability of the model proposed. However, more
experimental results on variety of residual soils may lead to further reinforcement of the model
proposed.
Table 2 Soil Properties
Description
Test Pit-1 Test Pit-2 Test Pit-3 Test Pit-4 Test Pit-5
A B C D E F G H I J
Depth of sampling, m
1.40 3.80 2.00 3.90 1.60 3.70 1.60 3.80 1.70 3.80
Gravel (%) 7.60 16.80 2.40 9.20 0.60 1.40 1.40 7.30 1.40 1.40
Sand (%) 71.00 68.60 66.80 71.40 51.20 57.60 28.40 29.70 53.20 51.20
Silt + Clay
(%) 21.40 14.60 30.80 19.40 48.20 41.00 70.20 63.00 45.40 47.40
Liquid Limit
(%) 52.00 55.00 34.00 34.00 50.00 85.00 64.00 61.00 52.00 67.00
Plastic Limit
(%) 19.00 19.00 16.00 16.00 18.00 25.00 20.00 20.00 19.00 21.00
Plasticity
Index (%) 33.00 36.00 18.00 18.00 32.00 60.00 44.00 41.00 33.00 46.00
IS
Classificatio
n
SC SC SC SC SC SC CH CH SC SC
Free Swell
Index (%) 80.00 80.00 50.00 50.00 75.00
180.0
0 90.00 85.00 80.00
100.0
0
Degree of
Expansion
Mediu
m
Mediu
m
Mediu
m
Mediu
m
Mediu
m High
Mediu
m
Mediu
m
Mediu
m High
Field density
,kN/m3 19.13 17.85 20.47 20.44 19.98 19.56 19.55 22.10 18.33 21.43
Natural
moisture
content,% 14.32 8.54 9.03 14.22 14.22 13.03 13.07 9.31 4.21 15.24
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Dry Density,
kN/m3 16.73 16.44 18.77 17.90 17.49 17.30 17.29 20.22 17.59 18.60
Void ratio 0.58 0.61 0.41 0.48 0.51 0.53 0.53 0.31 0.51 0.43
Degree of
saturation, Sr 0.57 0.73 0.58 0.78 0.73 0.83 0.65 0.79 0.87 0.82
%passing
425 μ 28.6 23.9 42.6 34.4 66.2 55.6 82 67 73.4 62.2
Modified
Liquid
Limit,% 14.87 13.15 14.48 11.70 33.10 47.26 52.48 40.87 38.17 41.67
Void Ratio at
modified
Liquid Limit 0.394 0.348 0.384 0.310 0.877 1.252 1.391 1.083 1.011 1.104
Figure 1 Grain size distribution of the soil samples A-F
Figure 2 Grain size distribution of the soil samples G-J
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Figure 3 Compression paths of remolded soils in consolidometer
Figure 4 Normalized compression paths of remolded soils
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Figure 5 Compression paths of remolded and in-
situ soils (A&B)
Figure 6 Compression paths of remolded and in-
situ soils (C&D)
Figure 7 Compression paths of remolded and in-
situ soils (E&F)
Figure 8 Compression paths of remolded and in-
situ soils (G&H)
Figure 9 Compression paths of remolded and in-situ soils (I&J)
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Figure 10 Compression paths of in-situ soils (A-I)
Figure 11 Normalized compression paths of in-situ soils
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Figure 12 Predicted Compression Path at 0.5m
depth
Figure 13 Predicted Compression Path at 1.00m
depth
Figure 14 Predicted Compression Path at 2.50m
depth
Figure 15 Predicted Compression Path at 3.00m
depth
Figure 16 Predicted Compression Path at 4.00m
depth
Figure 17 Predicted Compression Path at 5.00m
depth
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Figure 18 Predicted Compression Path of Allophane Residual Clay (Indonesia)
7. CONCLUDING REMARKS
The following Concluding Remarks may be made based on the limited experimental program
on residual soils of Tirupati Region
The compression paths of the remolded soil are found to be linear and these compression
paths when normalized with the void ratio corresponding to respective modified liquid
limit values gives a unique path as give by:
v
mle
eln18.0424.1
This expression can be vied as Intrinsic Compression Line which serves as basis for
estimating the in-situ state of the residual soil. If the compression paths of undisturbed
soil fall above the Intrinsic Compression Line, the soil is in meta-stable state
characterized by cementation. On the other hand if the compression path of undisturbed
soil is positioned on left and side of Intrinsic Compression Line, the soil deposit may be
said as over consolidated
The compression behaviour is characterized by initially rigid response and with
noticeable change in void ration at later stages of loading. Most geo-materials found in
tropical residual deposits are structured in nature and this natural structure affects the
behavior of tropical soils. Structural features affecting soil behavior include soil
cementation and soil fabric and stress history
The residual soils show variable compression behaviour. Some show distinct yield
pressures and some show gradual reduction in void ratios depending on relative
dominance of structural and pre-stress influences depending on location
The compression paths of undisturbed soils are identical though there are minor
deviations owing to changes in initial void ratio and moisture content
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The compression paths of the undisturbed soils can be normalized with initial void ratio
giving rise to a unique expression with regression coefficient of 0.969.
969.09963.0 20004.0
0
Ree
ev
This turns out that the initial void ratio which is a state parameter for any soil governs
the compression response of residual soils
The compression paths of Sudan Residual Clay and Indonesian Allophane Residual
clays are predicted with reasonable degree of accuracy indicating the applicability of
the phenomenological model observed.
ACKNOWLEDGEMENT
The authors profoundly acknowledge the facilities extended by SV University for collecting
the soil samples and conducting experiments without which this work would not have been
possible
REFERENCES
[1] Ahmed Syed Iftekhar & Siddiqua Sumi (2016), “Compressibility Behavior of Soils: A
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