Open Journal of Soil Science, 2012, 2, 320-332
http://dx.doi.org/10.4236/ojss.2012.23038 Published Online September 2012 (http://www.SciRP.org/journal/ojss)
A Model Study on Accelerated Consolidation of Coir
Reinforced Lateritic Lithomarge Soil Blends with Vertical
Sand Drains for Pavement Foundations
George Varghese, Hegde Ramakrishna, A. G. Nirmal Kumar, L. Durga Prashanth, G. Santosh
Department of Civil Engineering, National Institute of Technology Karnataka, Surathkal, India.
Received May 12th, 2012; revised June 10th, 2012; accepted June 24th, 2012
ABSTRACT
Sub-grade soils of lateritic origin encountered in the construction of highway embankments in various regions of India,
often comprise intrusions of soft lithomargic soils that result in large settlements during constructions, and differential
settlements at later stages. This necessitates the use of appropriate soil improvement techniques to improve the
load-carrying capacity of pavements. This work deals with accelerated consolidation of un-reinforced and coir-rein-
forced lateritic lithomargic soil blends, provided with three vertical sand drains. The load-settlement characteristics
were studied for various preloads ranging from 50 kg (0.0013 N/mm2) to 500 kg (0.013 N/mm2) on soil specimens pre-
pared in circular ferrocement moulds. It was observed that at lower preloads up to 200 kg, across the blends, the relative
increase in consolidation (Rct) for randomly reinforced soil with vertical drains was significantly higher than that of
un-reinforced soil without vertical drains, with an average value of 124.8%. Also, the Rct for un-reinforced soil with
vertical drains was quite higher than that of un-reinforced soil without vertical drains, with an average value of 103.9%.
In the case of higher preloads, the Rct values for randomly reinforced soil with vertical drains were moderate with an
average value of 30.88%, while the same for un-reinforced soil with vertical drains was about 20.4%. The aspect-ratio
of coir fibers used was 1:275.
Keywords: Vertical Sand Drains; Accelerated Consolidation; Settlement; Coir Reinforcement; Laterite; Shedi;
Lithomarge
1. Introduction
Construction and maintenance of pavements in water-
logged areas pose challenging problems to engineers.
The defects in road sub-grades mainly arise due to poor
compaction and consolidation. This is of major concern
in road-works associated with submersible areas. Incor-
porating the use of natural fibers in soil-stabilization,
along with the laying of natural fiber reinforced vertical
sand drains can contribute towards strengthening of road
sub-grades especially in the construction of highway em-
bankments.
Differential settlement of sub-grade soils cause dam-
ages to pavements in many regions. The problem as-
sumes critical importance in clayey and silty soil sub-
grades that have low permeability values. In such soils,
the consolidation and the resultant settlements occur over
a longer time-span. This work focuses on conducting
extensive studies on the consolidation characteristics of
weak soil sub-grades.
Natural geo-textiles made of coir or jute can be effect-
tively employed in the improvement of sub-grade strength
by accelerating the drainage of soil-moisture content re-
sulting in enhanced consolidation.
The name laterite was initially suggested by Francis
Buchanan [1] to describe “ferruginous, vesicular, un-
stratified, and porous soil with yellow ochre’s due to
high iron content, occurring in Malabar, India”. In the
district of Dakshina Kannada, and Udupi, laterite soil can
be found to occur above underlying shedi soil (or fine
silty soil). Laterite soil is quite stronger than shedi soil
due to the higher content of oxides of iron, while shedi
soils are characterized by low bearing strengths under
moist conditions.
In India, lithomargic clays are often found to occur at
depths of 1 - 3 meters below the top lateritic outcrops
throughout the western coastal areas extending from
Trivandrum to Mumbai, and also in the areas adjoining
the Deccan Plateau. Shedi soil is the name given to the
locally available whitish, pinkish or yellowish lithomar-
gic soils with high silt content, and low bearing strengths.

A Model Study on Accelerated Consolidation of Coir Reinforced Lateritic Lithomarge Soil Blends with
Vertical Sand Drains for Pavement Foundations
321
These soils are formed by weathering of soils in tropical
regions, and contain hydrated alumina, primary silicates,
and kaolinite. Lithomargic soils comprise 50% - 90%
lateritic constituents, while soils with 25% - 50% laterite
content are known as lateritic lithomarges.
2. Scope and Objectives of the Present Study
In order to attain higher bearing strengths in soft soils, it
may be required to resort to accelerated consolidation
during the construction stage by applying incremental
loads on suitably prepared sub-grades in stages. The
pore-water pressure that builds up under the overburden
pressure and surcharge loads, can be released with the
use of natural reinforcements especially on weak soils.
Additionally, the use of vertical drains will shorten the
length of the horizontal drainage-paths, and accelerate
the consolidation process. The enhanced dissipation of
pore-water pressure due to the presence of natural fiber
reinforcements and the overburden pressures, will result
a further acceleration of the consolidation process in lat-
eritic and shedi (L-S) soil sub-grades of embankments.
The natural degradation of natural fibers after a few years
[2] will not affect the strength and stability of L-S soil
sub-grades due to the reason that the soil layers would
have attained consolidation in the meantime.
The present work deals with investigations on load-
settlement characteristics due to accelerated consolida-
tion of various blends of laterite and lithomargic (shedi)
soils, with and without the use of reinforcements of ran-
domly dispersed coir-fibers, and with and without the use
of vertical sand drains randomly reinforced with coir.
This study also incorporates an assessment of the im-
provement in the California Bearing Ratio (CBR) values
of L-S soil, when randomly mixed with coir for soaked
and un-soaked conditions.
The objectives of the present study include the fol-
lowing:
 To prepare blended laterite-shedi (L-S) soil compris-
ing 25% laterite and 75% shedi soil, and to perform
basic laboratory investigations such as grain size
analysis, Atterberg’s limits, CBR tests, tests for stan-
dard and modified compaction tests for L-S soil sam-
ples as specified by Indian Standard (IS) codes.
 To measure the load-settlement properties and con-
solidation of fully saturated confined and un-rein-
forced L-S soil without the use of vertical drains for
soil samples drained at the top and bottom.
 To measure the load-settlement properties and con-
solidation of fully saturated confined and un-rein-
forced L-S soil with the use of 3 vertical drains.
 To measure the load-settlement properties and con-
solidation of fully saturated confined randomly rein-
forced L-S soil provided with 3 vertical drains
 In the case of tests on blended L-S soils, an optimum
fiber content of 1.0% of coir fiber was adopted for
random reinforcement.
 The sand-drains were fabricated using sand randomly
reinforced with 1% of coir fibers. Loosely-woven jute
fabric stitched at the seams was used in the installa-
tion of sand-drains of 10 cm diameter.
 The results were compared with the same for 50%
laterite + 50% shedi soil samples [3], and 100% shedi
[4] obtained in similar studies.
3. Literature Review
Studies on the stability of loaded footings on reinforced
soil using natural “iko” vegetable fibers, reported by Ak-
inumusura and Akinbolade [5] indicated that a significant
improvement in soil strength could be achieved.
Investigations on using vertical drains made of natural
fiber such as jute and coir for soil improvement simulat-
ing field conditions, was reported by Lee et al. [6]. The
studies revealed that the axial filter permeability of fiber
drains was higher than 10-5 m/sec for consolidation pres-
sures of up to 400 kN/m2.
Similar investigations in the field of application of
coir-fibers [7,8] highlighted the advantages in the use of
natural fibers for stabilization of embankments associ-
ated with the use of fiber-reinforced vertical drains.
Stapelfeldt [9] reported that preloading and the use of
vertical drains, can enhance the shear strength of the soil,
resulting in reduced soil compressibility, and permeabi-
lity prior to construction, preventing differential settle-
ments.
Comparative studies on soft clay soils of Bangkok by
Bergado et al. [10] revealed the use of compacted granu-
lar piles (CGP), and prefabricated vertical drains (PVD).
The studies indicated that in the case of soils improved
with PVDs, the settlement rates were higher by 30% -
35% when compared to soils improved using CGPs.
It was also noticed by Gosavi et al. [11] that the inclu-
sion of randomly distributed fibers of jute and coir, in
black cotton soils, increased the CBR values of clayey
sands (SW) and sandy-silt (SM) by about 96%.
Terzaghi [12] provides the basic theory for such one-
dimensional consolidation for saturated conditions and
also provides the strain formulation. The relationship be-
tween the final settlement (Sf) and the settlement (St) at
time t was expressed as:
tv
SUS
f

 (1)
The expression for Uv, the average degree of consoli-
dation at depth z at any instant t was given by Terzaghi
[13] as,

A Model Study on Accelerated Consolidation of Coir Reinforced Lateritic Lithomarge Soil Blends with
Vertical Sand Drains for Pavement Foundations
322

2
0
=12 exp
v
m
UM



 
2
v
MT (2)
where Tv = time factor (non dimensional) = (Cvt)/H2; Cv
= coefficient of vertical consolidation (m2/s) = k/ (γwmv);
k = permeability coefficient; mv = coefficient of volume
compressibility = av/(1+e0); e0 = initial void ratio; av =
coefficient of compressibility = ∆e/∆p; t = time in seconds;
H = total distance of drainage path which is equal to the
thickness of the layer (in m.) for soil subjected to top
drainage, and is equal to half of the thickness of the layer
(in m) for soils drained at the top and the bottom. The
expression for M is given as,

π212 for0,1,2
M
mm a
. (3)
From the above formulation, it is evident that consoli-
dation is dependent on the permeability of the medium.
Therefore, it is expected that the use of vertical drains
will have a profound effect on accelerating the consoli-
dation process.
4. Materials Used
Laterite, and Shedi soil: Laterite soil (obtained from a
site adjoining the newly widened National Highway-17,
near NITK, Surathkal, Mangalore), and shedi soil (ob-
tained from a road construction site close to Vidyanagara,
Kulai, Mangalore), were collected in water-proof poly-
thene bags, transported to the laboratory, and spread on
flat trays of size, 1500 mm × 900 mm. The lumps were
broken down using rammers, and the soil was sun-dried
for 10 days, until the weight of soil on the trays was
found to be constant, indicating that the soil was mois-
ture-free. The laterite and shedi soil fractions were then
intermixed 5 times using the technique of quartering. The
basic soil properties including OMC (optimal moisture
content), and MDD (maximum dry-density) were deter-
mined.
Sand: Locally available river-sand passing through
4.75 mm IS sieve with a coefficient of curvature (Cc) of
0.82, and a uniformity coefficient (Cu) of 1.7, was used
for the preparation of vertical drains. The sand selected
satisfies the general requirements of permeability and
piping as suggested by Khanna and Justo [14].
Coir: In the present study, coir fibers were purchased
from the local market. This comprised of brown coir fi-
bers with aspect ratios of about 275 and an average di-
ameter of 0.18 mm. The average length of the fibers used
in this study was maintained at 50 mm. Rao et al. [15]
suggested the use of 0.5% to 1% of coir fiber by weight
of sand, and also proved that the use of fibers will restrict
the lateral deformation at the peripheral areas of sand
drains. Accordingly, in the present study, 1.0% of coir-
fiber by weight of sand was used in preparing randomly
distributed fiber-reinforced vertical sand drains.
5. Determination of Optimal Fiber Content
for Soil Samples Using CBR Tests
CBR tests were conducted as per IS 2720: Part VII (1983)
[16]. with various percentages of coir fiber content ran-
domly reinforced with 0.25%, 0.5%, 0.75%, 1.0%, and
1.25% of coir, and the CBR values at 2.5 mm and 5 mm
penetrations were noted for soaked and un-soaked soil
samples. The CBR values were determined for the soil
samples, and the optimum fiber contents are reported as
in Table 1.
6. Tests for Consolidation
The test for accelerated consolidation involves several
stages such as, preparation of the soil sample, soaking of
specimens, loading, and installation of vertical drains and
preloading of soil samples. The soil sample to be tested
was prepared as mentioned above, and the water contents
required to prepare soil beds at 80% MDD were deter-
mined from the compaction curves. It was decided to
perform tests at moisture content lesser than the OMC in
order to study the load-settlement characteristics effect-
tively.
7. Experimental Setup and Methodology
Investigations were conducted for reinforced and un-
reinforced soil specimens, with and without installation
of vertical drains. These tests were conducted in order to
evaluate the improvement in the bearing capacity due to
the accelerated consolidation.
7.1. Tests for Consolidation of Un-Reinforced
Soil without Using Vertical Drains
In order to study the compressibility and consolidation of
soil sample, a ferro-cement cylindrical test mould was
used, of 740 mm internal diameter, 850 mm height, and
30 mm wall thickness. The test mould was provided with
an inlet pipe at the top and an outlet pipe at the bottom,
both of 20 mm diameter, to permit soaking of the soil
sample, and drainage of water. The test mould was
placed on leveled ground.
A sand layer of 100 mm thickness was provided at the
bottom of the Ferro-cement tank to act as a permeable
layer, and was compacted to a density of 1.53 g/cc.
Table 1. Optimum fiber contents (OFC) determined for
various blends.
Sl. noSoil Blends OMC (%) OFC (%)
1 100% Shedi 19 1.0
2 25% L + 75% S 15 1.0
3 50% L + 50% S 14 0.75

A Model Study on Accelerated Consolidation of Coir Reinforced Lateritic Lithomarge Soil Blends with
Vertical Sand Drains for Pavement Foundations
323
Above this layer, a jute textile was provided to act as a
separator. Over this, three layers of the soil sample, each
of 200 mm thickness, were placed and compacted to 80%
of the MDD. The soil and the sand layers were com-
pacted to the desired thickness, and respective densities
using a steel rammer (of 885 mm height, 140 mm dia-
meter, and 11.5 kg weight) and a wooden rammer (of
870 mm height, 40 mm diameter, and 1.17 kg weight).
On top of the three layers of compacted soil sample, a
layer of jute textile was placed. A layer of sand of 100
mm thickness compacted to a density of 1.53 g/cc was
provided at the top, to act as level-surface for the appli-
cation of preloads.
The soil sample in the cylindrical test mould possesses
the same characteristics as mentioned in the sections
above. A flat surface made of treated perforated plywood
(of 730 mm diameter, and 12 mm thickness) was pro-
vided above the sand layer. A schematic diagram of the
test set up is shown in Figure 1. The details of the com-
ponents used in this experiment are listed below:
1) Ferro-cement mould of cylindrical shape
2) 100 mm thick layer of sand at the bottom
3) Bottom layer of jute-textile as a separator
4) Three layers of soil, each of 200 mm thickness
5) Top layer of jute-textile as a separator
6) Top layer of sand of 100 mm thickness
7) Loading platform of treated plywood
8) Standard steel weights
9) Dial gauges of 0.01 mm least count
10) Water inlet
11) Water outlet
7.2. Tests on Consolidation of Un-Reinforced
Soil Using Three Vertical Drains
The test setup and procedure for test on consolidation of
un-reinforced soil sample are the same as that explained
above. A Ferro-cement cylindrical test mould with verti-
cal drains of 100 mm diameter and 600 mm height is
installed in a triangular pattern such that the center to
center distance between the adjacent drains is 350 mm.
This arrangement is considered to be more effective as it
is expected to result in uniform consolidation between
the drains due to the uniform center to center distances,
when compared to vertical drains installed in a square
pattern. The radius of influence (R) of a vertical drain
depends upon the spacing (S) between drains. In the case
of cylindrical drains installed in triangular pattern the
radius of influence (R) can be computed from the em-
pirical formula,
0.546RS (4)
Thus for vertical drains of 100 mm diameter and cen-
ter to center spacing of 350 mm between the drains, the
4
1
5
8
9
2
3
7
6
11
10
Figure 1. Schematic diagram of the test setup without ver-
tical drains.
radius of influence can be obtained as 190 mm based on
Equation (4). The vertical drains of 600 mm height were
installed with the help of sampling tubes of 100 mm di-
ameter inserted into sleeves made of jute fabric. See
Figure 2, Figures 3(a)-(d) provide a clear view of the
installation of vertical drains.
The sampling tubes enclosed in the jute sleeves, were
then filled in two layers with sand randomly mixed with
1% of coir fibers by weight of sand for a height of 200
mm by compacting with a wooden tamping tool with 15
blows per layer to obtain a compacted density of 1.08
g/cc. The tubes were gradually withdrawn when each
layer of soil sample of 100 mm was compacted. Smears
developed due to the disturbance to the soil while in-
stalling vertical drains, can result in reduced soil perme-
ability around the smear zone, restricting the rate of con-
solidation. However, in this investigation, since the ver-
tical drains were installed in a simultaneous build-up pro-
cedure, the smear effects are assumed to be negligible.
Jute Textiles
Woven jute textile fabric of 600 g per sq.m and 1.43 mm
thickness was used in fabricating the sleeves for the ver-
tical drains. The properties of jute textiles used in this
study are given in Table 2. Mild steel sleeves of 100 mm
average diameter and 600 mm height were used to build-
up the vertical drains to span the entire depth of laterite
soil tested.

A Model Study on Accelerated Consolidation of Coir Reinforced Lateritic Lithomarge Soil Blends with
Vertical Sand Drains for Pavement Foundations
324
200mm
R = 190 mm
S = 350 mm
100 mm
Figure 2. Influence zone for triangular pattern of drains
(Stapelfeldt, 2006).
7.3. Tests on Consolidation of Randomly
Reinforced Soil Using Three Vertical Drains
In this part of the experiment, the soil used in the test
mould was randomly reinforced using coir. The optimum
fiber content of 1.0% by weight of soil was adopted in
these tests. The overall experimental setup remains the
same as explained above.
8. Results
8.1. Soil Blend Type: 50% L + 50% S
The load-settlement details are discussed below for un-
reinforced soil samples without vertical drains (UR), un-
reinforced soil samples with vertical drains (UR-VD),
and reinforced soil samples with vertical drains (RR-
VD).
8.1.1. Settlement for UR (50% L + 50% S)
Figure 4(a) provides details on the load-settlement char-
acteristics for un-reinforced soils comprising 50% laterite
and 50% shedi soil. Also, Table 3(a) provides details on
the coefficient of consolidation (Cv) for various preloads
for the soil sample tested. It can be observed that during
the initial stages of loading using preloads of 50 kg, 100
kg, 150 kg, 200 kg and 250 kg, the compaction of soil is
considered to have taken place. This can be visualized
from the corresponding increase in the rate of compact-
tion in the above table. Thereafter, the rate of compaction
for preloads of 300 kg to 500 kg shows a decreasing
trend, indicating the commencement of the consolidation
process.
8.1.2. Settlement for UR-VD (50% L + 50% S)
Figure 4(b) provides details on the load-settlement char-
(a)
(b)
(c)
(d)
Figure 3. (a) Installation of vertical drains; (b) Removal of
casing for the third vertical drain; (c) Test mould with ac-
cessories for vertical drains; (d) Test mould with accessories
for vertical drains.

A Model Study on Accelerated Consolidation of Coir Reinforced Lateritic Lithomarge Soil Blends with
Vertical Sand Drains for Pavement Foundations
325
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
036912 15 18
Square-root of time [√(minute)]
Dial Guage Readings (mm)
50kg100kg 150kg200kg 250kg
300kg 350kg400kg 450kg500kg
(a)
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
03691215 18
Square- root of time [√(minute)]
Dial Guage Readings (mm)
50kg 100kg 150kg 200kg 250kg
300kg 350kg 400kg 450kg 500kg
(b)
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
03691215
Square- root of time [√(minute)]
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18
50kg 100kg 150kg200kg 250kg
300kg 350kg 400kg 450kg 500kg
(c)
Figure 4. (a) Load-settlement: UR (50% L + 50% S) soils;
(b) Load-settlement: UR-VD (50% L + 50% S) soils; (c)
Load-settlement: RR-VD (50% L + 50% S) soils.
Table 2. Properties of jute textiles used in this investigation.
Property Woven Type
Weight, gm per sq.m 600
Thickness, mm 1.43
Wrap × Weft per 100 sq. mm 28 × 34
acteristics for un-reinforced vertically drained soils com-
prising 50% laterite and 50% shedi soil. Table 3(b) pro-
Table 3. (a) Cv values: UR (50% L+50% S) soils; (b) Cv val-
ues: UR-VD (50% L + 50% S) soils; (c) Cv values: RR-VD
(50% L + 50% S) soils.
(a)
Co-efficient of consolidation Cv
Preload (kg) Cv
50 1.2351
100 1.2966
150 1.3365
200 1.4565
250 1.6830
300 1.5428
350 1.3644
400 1.2977
450 1.2711
500 1.1923
(b)
Co-efficient of consolidation Cv
Preload (kg) Cv
50 1.0805
100 1.4244
150 2.0567
200 1.7394
250 1.5999
300 1.5614
350 1.4898
400 1.1785
450 1.1239
500 1.1473
(c)
Co-efficient of consolidation Cv
Preload (kg) Cv
50 1.0894
100 1.4241
150 2.0784
200 1.9932
250 1.6400
300 1.6296
350 1.4895
400 1.2707
450 1.1574
500 1.0894

A Model Study on Accelerated Consolidation of Coir Reinforced Lateritic Lithomarge Soil Blends with
Vertical Sand Drains for Pavement Foundations
326
vides details on the coefficient of consolidation (Cv) for
various preloads for the soil sample tested. In this case, it
can be seen that during the initial stages of loading, as in
the case of preloads of 50 kg, 100 kg, and 150 kg, the
compaction of soil is considered to have taken place.
Thereafter, the rate of compaction for preloads of 200 kg
to 500 kg shows a decreasing trend, indicating the com-
mencement of the consolidation process.
8.1.3. Settlement for RR-VD (50% L + 50% S)
Figure 4(c) illustrates details on the load-settlement cha-
racteristics for randomly-reinforced vertically drained soils
comprising 50% laterite and 50% shedi soil. Table 3(c)
gives details on the coefficient of consolidation (Cv) for
various preloads. It can be observed that in the initial
stages of loading, the behavior of the soil is almost the
same as observed in the case of UR-VD (50% L + 50% S)
soil. The rate of compaction for preloads of 200 kg to
500 kg shows decreasing trend, indicating the com-
mencement of the consolidation process.
8.2. Soil Blend Type: 25% L + 75% S
8.2.1. Settlement for UR (25% L + 75% S)
Figure 5(a) provides details on the load-settlement char-
acteristics for un-reinforced soils comprising 25% laterite
and 75% shedi soil. Also, Table 4(a) provides details on
the coefficient of consolidation (Cv) for various preloads
for the soil sample tested. Here, the compaction of soil is
seen to have taken place up to preloads of 300 kg. The
rate of compaction for preloads of 350 kg to 500 kg
shows a decreasing trend, indicating the commencement
of the consolidation process.
8.2.2. Settlement for UR-VD (25% L + 75% S)
Figure 5(b) provides details on the load-settlement char-
acteristics for un-reinforced vertically drained soils com-
prising 25% laterite and 75% shedi soil. Table 4(b) pro-
vides details on the coefficient of consolidation (Cv) for
various preloads. Here, the compaction of soil is seen to
have taken place up to preloads of 200 kg. The rate of
compaction for preloads of 250 kg to 500 kg shows a
decreasing trend, indicating the commencement of the
consolidation process.
8.2.3. Settlement for RR-VD (25% L + 75% S)
Figure 5(c) provides details on the load-settlement char-
acteristics for randomly-reinforced vertically drained soils
comprising 25% laterite and 75% shedi soil. Table 4(c)
provides details on the coefficient of consolidation (Cv)
for various preloads. Here too, the compaction of soil is
seen to have taken place up to preloads of 200kg as in the
case of UR-VD (50% L + 50% S) and UR-VD (25% L +
75% S) soils. The rate of compaction for preloads of
Table 4. (a) Cv values: UR (25% L + 75% S) soils; (b) Cv
values: UR-VD (25% L + 75% S) soils; (c) Cv values:
RR-VD (25% L + 75% S) soils.
(a)
Co-efficient of consolidation Cv
Preload (kg) Cv
50 1.0380
100 1.1331
150 1.2415
200 1.2813
250 1.3224
300 1.4770
350 1.2966
400 1.2035
450 1.1946
500 1.1673
(b)
Co-efficient of consolidation Cv
Preload (kg) Cv
50 1.0379
100 1.2812
150 1.4602
200 1.6798
250 1.5103
300 1.4600
350 1.3661
400 1.1326
450 1.0994
500 1.0681
(c)
Co-efficient of consolidation Cv
Preload (kg) Cv
50 1.0378
100 1.3664
150 1.8790
200 1.9538
250 1.5642
300 1.5104
350 1.4601
400 1.2033
450 1.1327
500 1.0996

A Model Study on Accelerated Consolidation of Coir Reinforced Lateritic Lithomarge Soil Blends with
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0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
03691215
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Dial Guage Readings (mm)
18
50kg 100kg 150kg200kg250kg
300kg 350kg 400kg 450kg500kg
(a)
0.0000
0.1000
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0.4000
0.5000
0.6000
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Square-root of time [√(minute)]
Dial Guage Readings (mm)
50kg100kg 150kg200kg 250kg
300kg 350kg400kg 450kg500kg
(b)
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0.1000
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50kg100kg 150kg200kg 250kg
300kg 350kg 400kg 450kg500kg
(c)
Figure 5. (a) Load-settlement: UR (25% L + 75% S) soils;
(b) Load-settlement: UR-VD (25% L + 75% S) soils; (c)
Load-settlement: RR-VD (25% L + 75% S) soils.
250 kg to 500 kg shows a decreasing trend, indicating the
commencement of the consolidation process.
8.3. Soil Blend Type: 0% L+100% S
8.3.1. Settlement for UR (0% L + 100% S)
Figure 6(a) provides details on the load-settlement char-
acteristics for un-reinforced soils comprising 100% shedi
soil. Also, Table 5(a) provides details on the coefficient
of consolidation (Cv) for various preloads for the soil
sample tested. Here, the compaction of soil is seen to
have taken place up to preloads of 300 kg. The rate of
compaction for preloads of 350 kg to 500 kg shows a
decreasing trend, indicating the commencement of the
consolidation process.
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
03691215 18
Square- root of time [√(minute)]
Dial Guage Readings (mm)
50kg 100kg 150kg200kg 250kg
300kg 350kg 400kg450kg 500kg
(a)
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
0 36 9121518
Square- root of time [√(minute)]
Dial Guage Readimgs (mm)
50kg100kg150kg 200kg250kg
300kg 350kg400kg 450kg500kg
`
(b)
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
036912 1518
Square- root of time [√(minute)]
Dial Guage Readings (mm)
50kg 100kg 150kg 200kg 250kg
300kg 350kg 400kg450kg 500kg
(c)
Figure 6. (a) Load-settlement: UR (0% L + 100% S) soils;
(b) Load-settlement: UR-VD (0% L + 100% S) soils; (c)
Load-settlement: RR-VD (0% L + 100% S) soils.

A Model Study on Accelerated Consolidation of Coir Reinforced Lateritic Lithomarge Soil Blends with
Vertical Sand Drains for Pavement Foundations
328
Table 5. (a) Cv values: UR (0% L+100% S) soils; (b) Cv val-
ues: UR-VD (0% L + 100% S) soils; (c) Cv values: RR-VD
(0% L + 100% S) soils.
(a)
Co-efficient of consolidation Cv
Preload (kg) Cv
50 1.0176
100 1.0216
150 1.0467
200 1.0821
250 1.1250
300 1.4349
350 1.2517
400 1.2219
450 1.1768
500 1.1555
(b)
Co-efficient of consolidation Cv
Preload (kg) Cv
50 1.0214
100 1.1673
150 1.3661
200 1.5951
250 1.4939
300 1.4598
350 1.3233
400 1.1326
450 1.0375
500 1.0088
(c)
Co-efficient of consolidation Cv
Preload (kg) Cv
50 1.0092
100 1.3240
150 1.8277
200 1.8782
250 1.5638
300 1.5101
350 1.4113
400 1.2032
450 1.0993
500 1.0208
8.3.2. Settlement for UR-VD (0% L + 100% S)
Figure 6(b) provides details on the load-settlement cha-
racteristics for un-reinforced vertically drained soils
comprising 100% shedi soil. Table 5(b) provides details
on the coefficient of consolidation (Cv) for various pre-
loads. Here, the compaction of soil is seen to have taken
place up to preloads of 200 kg. The rate of compaction
for preloads of 250 kg to 500 kg shows a decreasing
trend, indicating the commencement of the consolidation
process.
8.3.3. Settlement for RR-VD (0% L + 100% S)
Figure 6(c) provides details on the load-settlement char-
acteristics for randomly-reinforced vertically drained
soils comprising 100% shedi soil. Table 5(c) provides
details on the coefficient of consolidation (Cv) for various
preloads. Here too, the compaction of soil is seen to have
taken place up to preloads of 200kg as in the case of
UR-VD (50% L + 50% S) and UR-VD (25% L + 75% S)
soils. The rate of compaction for preloads of 250 kg to
500 kg shows a decreasing trend, indicating the com-
mencement of the consolidation process.
9. Comparisons of Settlements of UR with
UR-VD, and RR-VD Soils for Blends of
Lateritic Lithomarge
9.1. UR vs UR-VD, and RR-VD: 50% L + 50% S
Soils
Figure 7(a) provides details of the load-settlement trends
for a preload of 50 kg for UR, UR-VD, and RR-VD test
conditions for 50% L + 50% S soils. Similar figures can
be obtained and studied for preloads of 100 kg, 150 kg,
200 kg, 250 kg, 300 kg, 350 kg, 400 kg, 450 kg, and 500
kg.
On observation of the load-settlement trends for vari-
ous pre-loads, it was found that the 169th minute could
be taken as a reference for comparison, since the soil was
found to attain stability at this instance. In other words,
the soil can be assumed to have been consolidated at this
point in time.
The relative increase in consolidation achieved by un-
reinforced soil samples provided with vertical drains,
when compared to un-reinforced soil samples without
vertical drains is expressed using the percentage of the
increase in settlement of the soil sample provided with
vertical drains, to the settlement of the un-reinforced soil
without vertical drains. This is denoted as, Rct (UR v/s
UR-VD).
Similarly, the relative increase in consolidation achi-
eved by randomly reinforced soil samples provided with
vertical drains, when compared to un-reinforced soil
samples without vertical drains is expressed using the
percentage of the increase in settlement of the randomly

A Model Study on Accelerated Consolidation of Coir Reinforced Lateritic Lithomarge Soil Blends with
Vertical Sand Drains for Pavement Foundations
329
Table 6. (a) Relative increase in consolidation at different
preloads at the 169thminute of L-S; (b) Relative increase in
consolidation at different preloads at the 196th minute of
L-S; (c) Relative increase in consolidation at different pre-
loads at the 225th minute of L-S.
(a)
Preload
(kg)
Rct (UR vs UR-VD)
(%)
Rct (UR vs RR-VD)
(%)
50 38.61 64.64
100 50.17 79.65
150 65.16 87.33
200 37.44 61.32
250 02.12 15.44
300 12.21 14.33
350 14.25 31.13
400 11.36 24.24
450 08.22 18.53
500 10.73 18.79
(b)
Preload
(kg)
Rct (UR vs UR-VD)
(%)
Rct (UR vs RR-VD)
(%)
50 40.91 61.36
100 59.95 85.15
150 120.85 149.15
200 102.52 106.43
250 58.96 61.68
300 5.20 13.98
350 11.96 26.5
400 18.29 24.32
450 8.1 21.64
500 15.1 24.25
(c)
Preload
(kg)
Rct (UR vs UR-VD)
(%)
Rct (UR vs RR-VD)
(%)
50 40.61 57.73
100 120.49 172.84
150 275.26 325.15
200 294.55 321.6
250 152.02 168.44
300 5.95 15.33
350 7.37 20.40
400 4.01 18.69
450 7.98 17.65
500 13.06 20.10
reinforced soil sample provided with vertical drains, to
the settlement of the un-reinforced soil without vertical
drains. This is denoted as, Rct (UR vs RR-VD).
Table 6(a) provides details on the relative increase in
consolidation at different preloads at the 169th minute of
the load settlements for UR v/s UR-VD, and UR v/s
RR-VD observations. In this table, it is observed that for
pre-loads ranging from 50 kg to 200 kg, the effect of pro-
viding vertical drains was significant when compared to
the rate of settlement in the case of UR soils. The Rct (UR
v/s UR-VD) values within this range of pre-loads vary
from 37.14% to 65.29%. But for pre-loads higher than
200 kg, the effect of providing vertical sand drains was
not significant as it was found to vary between 2.13% to
14.35%.
Also, for the pre-loads ranging from 50 kg to 200 kg,
the effect of randomly reinforcing the soil was significant
when compared to the rate of settlement in the case of
UR soils. The Rct (UR v/s RR-VD) values were found to
range between 60.12% to 86.13%, whereas for pre-loads
greater than 200 kg, the increase was found to be moder-
ate with Rct (UR v/s RR-VD) values ranging between
14.33% to 31.04%.
Therefore, it can be seen that the combined effect of
vertical drains and random reinforcement with coir fibers
resulted in considerable increase in the rate of consolida-
tion at lower pre-loads.
9.2. UR vs UR-VD, and RR-VD: 25% L + 75% S
Soils
Figure 7(b) provides details of the load-settlement trends
for a preload of 50 kg for UR, UR-VD, and RR-VD test
conditions for 50% L + 50% S soils. Similar figures can
be obtained and studied for preloads of 100 kg, 150 kg,
200 kg, 250 kg, 300 kg, 350 kg, 400 kg, 450 kg, and 500
kg.
On observation of the load-settlement trends for vari-
ous pre-loads, it was found that the 169th minute could
be taken as a reference for comparison, since the soil was
found to attain stability at this instance.
Table 6(b) provides details on the relative increase in
consolidation at different preloads at the 169th minute of
the load settlements for UR v/s UR-VD, and UR v/s
RR-VD observations. In this table, it is observed that for
pre-loads ranging from 50 kg to 250 kg, the effect of pro-
viding vertical drains was significant when compared to
the rate of settlement in the case of UR soils. The Rct (UR
v/s UR-VD) values within this range of pre-loads vary
from 40.91% to 120.85%. But for pre-loads higher than
200 kg, the effect of providing vertical sand drains was
insignificant as it varied between 5.2% and 18.29%.
Also, for the pre-loads ranging from 50 kg to 250 kg,
the effect of randomly reinforcing the soil was significant

A Model Study on Accelerated Consolidation of Coir Reinforced Lateritic Lithomarge Soil Blends with
Vertical Sand Drains for Pavement Foundations
330
0.0000
0.0500
0.1000
0.1500
0.2000
0.2500
0.3000
0.3500
0.4000
0.4500
0.5000
0.5500
0.6000
0123456789101112131415161718
Dial Gauge Readings (mm)
Sqrt Time [√(minute)]
LoadSettlementCurve
UR_100kg UR‐VD_100kg RR‐VD_100kg
(a)
0.0000
0.0500
0.1000
0.1500
0.2000
0.2500
0.3000
0.3500
0.4000
0.4500
0.5000
0.5500
0.6000
0123456789101112131415161718
DialGaugeRead i ng s(mm)
SqrtTime[√(minute)]
LoadSettlementCurve
UR_100kg UR‐VD_100kg RR‐VD_100kg
(b)
0.0000
0.0500
0.1000
0.1500
0.2000
0.2500
0.3000
0.3500
0.4000
0.4500
0.5000
0.5500
0.6000
0123456789101112131415161718
DialGaugeReadings(mm)
SqrtTime[√(minute)]
LoadSettlementCurve
UR_100kg UR‐VD_100kg RR‐VD_100kg
(c)
Figure 7. (a) Load-settlement trend for preload of 100 kg for 50% L + 50% S soil; (b) Load-settlement trend for preload of
100kg for 25% L + 75% S soil; (c) Load-settlement trend for preload of 100kg for 0% L + 100% S soil.

A Model Study on Accelerated Consolidation of Coir Reinforced Lateritic Lithomarge Soil Blends with
Vertical Sand Drains for Pavement Foundations
331
when compared to the rate of settlement in the case of
UR soils. The Rct (UR v/s RR-VD) values were found to
range from 61.36% to 149.15%, whereas for pre-loads
greater than 250 kg, the increase was found to be moder-
ate with Rct (UR v/s RR-VD) values ranging from 13.98%
to 24.32%.
Therefore, it can be seen that the combined effect of
vertical drains and random reinforcement with coir fibers
resulted in considerable increase in the rate of consolida-
tion at lower pre-loads.
9.3. UR vs UR-VD, and RR-VD: 0% L + 100% S
Soils
Figure 7(c) provides details of the load-settlement trends
for a preload of 50 kg for UR, UR-VD, and RR-VD test
conditions for 50% L + 50% S soils. Similar figures can
be obtained and studied for preloads of 100 kg, 150 kg,
200 kg, 250 kg, 300 kg, 350 kg, 400 kg, 450 kg, and 500
kg.
On observation of the load-settlement trends for vari-
ous pre-loads, it was found that the 225th minute could
be taken as a reference for comparison, since the soil was
found to attain stability at this instance.
Table 6(c) provides details on the relative increase in
consolidation at different preloads at the225th minute of
the load settlements for UR v/s UR-VD, and UR v/s
RR-VD observations. In this table, it is observed that for
pre-loads ranging from 50 kg to 250 kg, the effect of
providing vertical drains was significant when compared
to the rate of settlement in the case of UR soils. The Rct
(UR v/s UR-VD) values within this range of pre-loads
vary from 40.61% to 294.55%. But for pre-loads higher
than 200kg, the effect of providing vertical sand drains
was not significant as it was found to vary between
4.01% and 13.06%.
Also, for the pre-loads ranging from 50 kg to 250 kg,
the effect of randomly reinforcing the soil was significant
when compared to the rate of settlement in the case of
UR soils. The Rct (UR v/s RR-VD) values were found to
range from 57.73% to 325.15%, whereas for pre-loads
greater than 250 kg, the increase was found to be moder-
ate with Rct (UR v/s RR-VD) values ranging from
15.33% to 20.40%.
Therefore, it can be seen that the combined effect of
vertical drains and random reinforcement with coir fibers
resulted in considerable increase in the rate of consolida-
tion at lower pre-loads, whereas a moderate increase was
observed at higher pre-loads.
10. Conclusions
The above sections focused on examining the rate of
consolidation for various types of soil mixes for various
test conditions using vertical drains. The observations
made as part of this work will have an important bearing
on the construction of road and railway embankments on
lateritic soil sub-grades.
Also, natural fibers of coir can be effectively used in
further accelerating consolidation since the fibers allow
pore-water pressures to dissipate easily when subjected
to overburden pressures. Also, coir, being a natural fiber,
undergoes decomposition once the soil attains sufficient
strength through consolidation.
Laboratory investigations were performed in this study,
for soil compacted in cylindrical moulds of 70 cm dia-
meter and 85 cm internal height for laterite soil blended
with 50% shedi soil (50% L + 50%S ), laterite soil blended
with 75% shedi soil (25% L+75% S) and shedi soil (0%
L + 100% S).Tests on drained soil samples were per-
formed by providing 3 vertical sand drains reinforced
with 1% coir fiber. The following are the conclusions
drawn from this study.
10.1. Soil Type: 50% L + 50% S
From Sections 8.1 and 9.1, and Table 6(a), it is seen that
the 50% L + 50% S soil type attained stability at around
the 169th minute after application of the preloads. Using
this as datum, it can be observed that for the pre-loads
ranging from 50 kg to 200 kg, the effect of randomly
reinforcing the soil was significant when compared to the
rate of settlement in the case of UR soils. The relative
increase in settlement of RR-VD soils when compared to
that of UR soils (Rct (UR v/s RR-VD)), was found to
range between 60.12% to 86.13%, with an average in-
crease of 71.73%, whereas for pre-loads greater than 200
kg, the increase was found to be moderate with Rct (UR
v/s RR-VD) values ranging between 14.13% to 31.04%,
with an average increase of 20.51%. Considering the
average values, for pre-loads ranging from 50 kg to 200
kg, there is an additional increase of 24.8% in the settle-
ment of randomly reinforced soil blends when compared
to that of soil blends with vertical drains alone. Hence it
can be concluded that in the soil blend of 50% L+50% S,
there is a significant increase in settlement due to random
reinforcement with coir fibers in addition to the vertical
drains.
10.2. Soil Type: 25% L + 75% S
From Sections 8.2 and 9.2, and Table 6(b), it is seen that
the 25% L+75% S soil type attained stability at around
the 196th minute after application of the preloads. Using
the same 196th minute as datum, it can be observed that
for the pre-loads ranging from 50 kg to 250 kg, the effect
of randomly reinforcing the soil in addition to providing
vertical sand drains, was significant when compared to

A Model Study on Accelerated Consolidation of Coir Reinforced Lateritic Lithomarge Soil Blends with
Vertical Sand Drains for Pavement Foundations
332
the rate of settlement in the case of UR soils. The relative
increase in settlement of RR-VD soils when compared to
that of UR soils (Rct (UR v/s RR-VD)), was found to
range between 61.36% and 149.15%, with an average
increase of 92.7%, whereas for pre-loads greater than
150 kg, the increase was found to be moderate, with Rct
(UR v/s RR-VD) values ranging between 13.98% to
24.32% with an average increase of 22.1%. Considering
the average values, for pre-loads ranging from 50 kg to
250 kg, there is an additional increase of 16.1% in the
settlement of randomly reinforced soil blends when com-
pared to that of soil blends with vertical drains alone.
Hence it can be said that for the soil blend of 25%L +
75% S, there is a significant increase in settlement due to
random reinforcement with coir fibers in addition to the
vertical drains.
10.3. Soil Type: 0% L + 100% S
From Sections 8.3 and 9.3, and Table 6(c), it is seen that
the 0% L+100% S soil type attained stability at around
the 225th minute after application of the preloads. The
225th minute is taken as a reference since the graphical
trends indicate that for the pre-loads ranging from 50 kg
to 250 kg, the effect of randomly reinforcing the soil in
addition to providing vertical sand drains, was significant
when compared to the rate of settlement in the case of
UR soils. The relative increase in settlement of RR-VD
soils when compared to that of UR soils (Rct (UR v/s
RR-VD)), was found to range between 57.73% and
325.15%, with an average increase of 209.1%, whereas
for pre-loads greater than 250 kg, the increase was found
to be moderate, with Rct (UR v/s RR-VD) values ranging
between 15.33% to 20.4% with an average increase of
18.43%. Considering the average values, for pre-loads
ranging from 50 kg to 250 kg, there is an additional in-
crease of 32.6% in the settlement of randomly reinforced
soil blends when compared to that of soil blends with
vertical drains alone. Hence it can be concluded that in
the soil blend of 0% L + 100% S, there is a significant
increase in settlement due to random reinforcement with
coir fibers in addition to the vertical drains.
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