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CIVIL AND ENVIRONMEN TAL ENGINEERING REP O R TS
E-
ISSN 2450-8594
CEER 2020; 30 (1): 171-184
DOI: 10.2478/ceer-2020-0013
Original Research Article
A PRELIMINARY COMPARATIVE STUDY OF SEEPAGE
BEHAVIOUR BEHIND RETAINING WALLS WITH CRUMB
RUBBER AND GEOCOMPOSITE
Vijayasimhan SIVAPRIYA
1
, Chinnusamy SUDHARASAN
2
,
Ravikumar SURAJ
2
, Kalyansundaram ABINAYA
2
Department of Civil Engineering, SSN College of Engineering, India
A b s t r a c t
A retaining wall is built to provide support to the soil when there is a change in elevation
of the ground. Weep holes present in the retaining wall help water to seep through it.
Filter protection should be made behind the weep holes to prevent soil erosion around
the weep holes. The classic filter material that is widely used is gravel, which is packed
according to Hudson’s law. Laboratory experiments were conducted to understand the
seepage function of alternative material such as crumb rubber and geocomposite
(fabricated) in a homogenous sand layer and in-situ soil. The time taken by the water to
reach the weep holes was calculated and compared. From the results, it is suggested to
use crumb rubber as an alternative packing material behind the weep hole.
Keywords: crumb rubber, geocomposite, permeability, experimental study
1. INTRODUCTION
A retaining wall is constructed to retain the soil on one side and making the
other side convenient for human purposes. It is designed for the following
stability conditions; safety against overturning, safety against sliding, safety
against allowable soil bearing pressure and stress within the components that are
1
Corresponding author: Department of Civil Engineering, SSN College of Engineering, Chennai,
India – 603110; e-mail: sivapriyasv@ssn.edu.in.
2
Department of Civil Engineering, SSN College of Engineering, India, Undergraduate students
172
Vijayasimhan SIVAPRIYA, Chinnusamy SUDHARASAN, Ravikumar SURAJ,
Kalyansundaram ABINAYA
within codal provisions (Brooks, 2010). The main cause of the retaining wall is
due to improper design and poor construction practice (Figure 1).
Fig. 1. Failure modes of reinforced earth wall (External failure (a) basal sliding, (b)
overturning, (c) bearing capacity failure, (d) overall sliding; internal failure (e) pull-out
failure, (f) breakage of reinforcement, (g) internal sliding, (h) breakage of connector, (i)
shear failure of facing wall, (j) failure of upper facing block) (Shin et al., 2011)
Soil and water interaction behaviour leads to various problems. When the water
penetrates into the voids of the soil, soil erosion takes place. Permeability is
defined as the velocity of flow under a hydraulic gradient of unity (Ranjan and
Rao, 2005). The piping effect occurs if the permeability of material used in
drains is not studied to a maximal extent. Hence, soil permeability behaviour
should be understood clearly.
A PRELIMINARY COMPARATIVE STUDY OF SEEPAGE BEHAVIOUR BEHIND
RETAINING WALLS WITH CRUMB RUBBER AND GEOCOMPOSITE
173
During rainy seasons, water tends to penetrate into the retained soil and seeps
through the weep holes. The purpose of these weep holes is to drain the water
into a proper drainage system, which is constructed along the bottom of the
retaining wall (Figure 2). If the water is not drained properly, hydrostatic
pressure built behind the retaining wall increases, where the retaining wall may
not be designed to carry that pressure. Due to high generation of hydrostatic
stress, the face of the retaining wall tends to crack (Figure 3) where the backside
of weep holes will have a soil packing from smaller particles to larger particles
towards the face of the retaining wall. In a recent trend, geocomposite material is
widely used as the cost reduces by 35% compared to a conventional system
(Pietro, 2013).
Few case studies discuss the erosion of soil slope and the importance of drains.
Leeves, an important flood protection structure, was damaged by improper
seepage. When the soil is mixed with short fibre as reinforcement (length 10 –
100 mm), it shows a high erosion resistance (Furumoto et al., 2002). Rainfall
intensity also plays a vital role in causing instability (Dahal et al., 2006), and
therefore should be considered as an important parameter while designing. In
addition, improper wall design against stability leads to failure of the retaining
wall (Souza et al., 2017).
Crumb rubber is a largely produced solid waste after recycling used tyres and
crumbed into uniform angular pieces. It was reported that every year, about 100
crores of used tyres were turned into crumb rubber (Thomas et al., 2014). This
solid waste was used widely in pavement and concrete as a replacement material
for aggregates.
In order to understand the importance of permeability characteristics of CR,
a laboratory study was conducted in homogenous sand and in-situ soil with
packing material as crumb rubber in single and triple layers near the weep holes.
To compare it with the modern material, geocomposite material (laboratory
fabricated) was used behind the weep holes.
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Vijayasimhan SIVAPRIYA, Chinnusamy SUDHARASAN, Ravikumar SURAJ,
Kalyansundaram ABINAYA
Fig. 2. Location of drains in retaining wall (Froehlich, 2017)
Fig. 3. Excessive settlement and deformation (a) cracking of facing wall, (b) differential
settlement of facing wall, (c) settlement of REW, (d) excessive settlement of facing wall,
(e) differential settlement of REW, (f) deformation of wall) (Lee and Cho, 2011)
A PRELIMINARY COMPARATIVE STUDY OF SEEPAGE BEHAVIOUR BEHIND
RETAINING WALLS WITH CRUMB RUBBER AND GEOCOMPOSITE
175
2. MATERIALS PROPERTIES
2.1. Soil Properties
For laboratory experiments, two soils were used: pure sand (S1) and in-situ soil
(S2), which were collected from the college premises. The characteristics of the
soil were found using Indian Standard codes (Table 1).
The particle size distribution of S1 and S2 is shown in Figure 4. From the graph,
Coefficient of Uniformity (c
u
) and Coefficient of Curvature (c
c
) is calculated by
the following equation (2.1,2.2).
10
60
D
D
c
u
=
(2.1)
1060
2
30
DD
D
c
c
=
(2.2)
Where, D
10
, D
30
and D
60
are the particle size corresponding to 10, 30 and 60 %
finer.
Table 1. Properties of the soil
Properties Values for Soil IS Code
S1 S2
c
u
2.857 9.2 IS 2720 (4) : 1985
c
c
1.03 0.735
Specific gravity 2.7 2.2 IS 2720 (3)-1980
Dry Density, kN/m
3
18.36 16.79 IS 2720 (7)- 1987
Optimum Mositure
Content, %
6.8 6
Angle of internal
friction, deg
38 38 IS 2720(13) -1986
Permeability,
mm/sec
2.105 x 10
-
3
IS 2720 (17) -1979
Classification SP (Poorly graded
sand)
SP (Poorly graded
sand)
IS 1498 -1970
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Vijayasimhan SIVAPRIYA, Chinnusamy SUDHARASAN, Ravikumar SURAJ,
Kalyansundaram ABINAYA
Fig. 4. Soil distribution curve
2.2. Materials used and its properties
Crumb rubber and geocomposite materials were used as drains for the
experiments and its properties were listed below;
1. Crumb Rubber (CR): Recycled material from used tires and its properties are
listed in Table 2. The reuse of used tires is an emerging engineering aspect. It
is widely used as replacement material in concrete for fine aggregate.
Table 2 . Properties of CR
Description and Properties Specification
Ash Content 4.0 - 5.5%
Acetone Extraction 7 - 10
Moisture Content 0.5 % Max
Carbon Black 20 - 25%
Specific Gravity 1.17
Fineness through 30 microns 100%
2. Geocomposite (GC): Due to its longevity, currently geocomposite materials
are widely used in reinforcing and stabilizing the soil. In the current study,
non- woven geotextile sandwiched with geogrid was used as a filter material
(laboratory fabricated – Figure 5) with its properties listed in table 3.
0
20
40
60
80
100
0.01 0.1 1 10
Percentgae Finer,%
Particle Size,mm
S1 S2
A PRELIMINARY COMPARATIVE STUDY OF SEEPAGE BEHAVIOUR BEHIND
RETAINING WALLS WITH CRUMB RUBBER AND GEOCOMPOSITE
177
Fig. 5. Geocomposite material
Table 3. Range of values for some properties of Geosynthetics
(Lawson and Kempton, 1995)
Types Thickness,
mm
Mass per
unit area,
gsm
Ultimate
max. tensile
strength,
kN/m
Extensio
n at max.
load, %
Apparent
opening
size, mm
Non-woven
geotextiles 0.25 - 0.75 100 -2000 5 - 100 20 - 100 0.02 - 0.6
Woven -
Geotextiles 0.25 - 3 100 - 1500 20 - 400 10 - 50 0.05 - 2
Geomembranes 0.25 - 3 250 - 3000 10 - 50 50 - 200 ≈ 0
Geogrids 5 - 15 200 - 1500 10 - 200 5 - 25 10 - 100
Geonets 3 - 10 100 - 1000 - - 5 - 15
3. METHODOLOGY
3.1 Test Tank Set-up
An acrylic tank of 0.3 x 0.3 x 0.3 m tank was fabricated with a scaling factor of
20 as per Buckingham π theorem.
The height of the wall was taken as 6 m, with a wall thickness of 1 m as per
Indian standard 14458 -1 for masonry retaining walls, with toe drain at a height
of 1 m above the foundation and central weep holes with spacing, not more than
3 m (Figure 6). A freeboard of 50 cm was left in the top of the soil. In order to
understand the mean behaviour of the permeability characteristics of soil behind
the retaining wall, weep holes were provided for seepage of water. Five weep
holes were made in an interlaced format with two holes in the top and bottom
and one hole in the centre; for the purposes of the study, a central hole was
considered.
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Vijayasimhan SIVAPRIYA, Chinnusamy SUDHARASAN, Ravikumar SURAJ,
Kalyansundaram ABINAYA
Fig. 6. Fabricated Tank
3.2 Sample Preparation
The prefabricated acrylic mould was coated with oil/grease in order to avoid
wall friction and leakage of water. Sandy (S1) soil was filled in a mould at an
optimum height of fall - 5 cm determined by relative density test for various
height of fall (Figure 7). In the case of in-situ soil (S2), the soil was cut from an
excavation pit and placed directly into the mould. The water was supplied to the
sample by maintaining constant head delivered from a height of 0.3 m. Initially,
all the holes were blocked, it was let open when the soil was fully saturated
(Figure 8). The water draining from the soil sample through weep holes was
collected and the corresponding time taken was noted.
Fig. 7. Height of fall Vs relative density
0
5
10
15
20
25
55 60 65 70
Heigth of Fall,mm
Relative Density%
A PRELIMINARY COMPARATIVE STUDY OF SEEPAGE BEHAVIOUR BEHIND
RETAINING WALLS WITH CRUMB RUBBER AND GEOCOMPOSITE
179
Fig. 8. Setup for the experiment
3.3 Placing of Material
CR: CR was packed at the back of the weep holes in single and three layers and
allowed for water to flow.
GC: The composite materials were placed near the central weep hole and then
the soil was filled.
4. RESULTS AND DISCUSSION
The test was conducted by keeping the water head as a variable – simulating the
falling head permeability condition. The time is taken to collect 1 litre of water
was measured.
Initially, all the tests were conducted by opening all the five weep holes upon
filling the test tank and the results were observed (Figure 9). As the holes were
closed initially and opened upon filling the tank, the time taken for the water to
flow through 5 weep holes was reduced by 66.3% compared to a single hole. As
the time taken was very quick, the central weep-hole alone was chosen for the
study.
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Vijayasimhan SIVAPRIYA, Chinnusamy SUDHARASAN, Ravikumar SURAJ,
Kalyansundaram ABINAYA
Fig. 9. Comparison of time taken between single and five weepholes
4.1 With S1 soil
For cohesionless, homogenous sand, the time taken to collect one litre of water
through single weep holes was 7.24 minutes. This value was considered as the
base value for further comparison.
Crumb rubber retained on 600-micron sieve (available size) was used in the back
of the weep hole, as smaller particles provided better seepage. However, usage
of CR reduced the time taken to seep by 26.52% and 53.45 % respectively for
single and multiple layers, for example 3 layers. It was observed during the
experiment that the CR started coming out of the weep holes and subsequently,
the CR packing was disturbed due to its finer particle size. In the case of GC, the
time taken had a reduction of about 39.64% (Figure 10).
4.2 With S2 soil
In order to understand the real-time behaviour of the soil, in-situ soil was used
for the tests collected from the college premises. Field soil, otherwise termed as
in-situ soil, showed a heterogeneous combination, which contains a negligible
percentage of fine particles. The presence of organic matter in the top of the soil
was removed manually, as it affects the water flow. The entire test for in-situ
soil was carried out by providing single weep holes.
The time taken to collect 1 litre of water through the in-situ sample was
calculated as 8.47 minutes, which was mainly due to the presence of
heterogeneity. When crumb rubber was placed near the weep holes, the time
Single Five
Serie1 7.24 2.44
0
2
4
6
8
10
Time Taken,min
A PRELIMINARY COMPARATIVE STUDY OF SEEPAGE BEHAVIOUR BEHIND
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181
was reduced to 5.58 minutes for a single layer. For multiple layers, the seepage
was increased to 50 minutes. During the experiments, it was observed that the
particles started moving and the larger particles clogged the weep holes,
resulting high time taken. In-situ soil with GC shows an appreciable behaviour
by reducing the seepage by 58.68 %, reducing the pressure acting on the wall
(Figure 11).
Fig. 10. Comparison of seepage for various materials - S1
Fig. 11. Comparison of seepage for various materials - S2
S1 S1+CR S1+CR in
layers S1+GC
Serie1 7.24 5.32 3.37 4.37
0
2
4
6
8
10
Time, min
S2 S2+CR S2+CR in
layer S2+GC
Serie1 8.47 5.58 50 3.5
0
10
20
30
40
50
60
Time, min
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Vijayasimhan SIVAPRIYA, Chinnusamy SUDHARASAN, Ravikumar SURAJ,
Kalyansundaram ABINAYA
There was a decrease in seepage time between 26 and 53.45 % for sandy soil
with crumb rubber (S1) as its packing material behind the weep holes; for
geocomposite material, the seepage time decreased to 39.64%. A non-
degradable man-made material, geocomposite showed a conventional reduction
in seepage time. S1 with three layers of crumb rubber showed more than a 30%
reduction in seepage time compared to S1+GC, which is highly appreciable. For
in-situ soil (S2), the decrease in seepage time was 34.12% for a single layer of
crumb rubber, and for geocomposite material it was 58.68%, which showed a
reduction in time by 42%. Hence, CR can be ideally reused in retaining walls for
drainage purposes, thus providing an effective avenue for water management.
Due to the difference in seepage behaviour of single and multiple layers of CR,
the function of multiple layers should be modelled in the laboratory before
commencing installation work in the field.
5. LIMITATIONS
In order to get a better understanding of the water flow, the top and bottom two
weep holes were closed by keeping the central hole open. The study is a basal
attempt to understand the seepage behaviour, hence the intensity of the rain is
not varied. As the study in this area is limited, an attempt on one to compare the
parameters considered was not possible due to the almount of literature in the
existing area.
6. CONCLUSIONS
From the experiment, the importance of seepage time when various materials are
used behind weep holes retaining walls is important. Here, the packing of
materials also showed a high degree of variation. If CR, a solid waste material, is
used as a single layer, it reduces the seepage time by 34%. In the case of
multiple layers, there was a reduction in time taken for homogenous sandy soil
and an increase in the time taken for in-situ soil as the coarser particles present
by nature itself act as a filter media and retard the seepage flow. This retardation
leads to stagnation of water over its freeboard thickness and reduces the time
taken. Due to the low permeability behaviour of GC, the time taken reduced for
both the soil types.
The largely available solid waste material (CR) showed good improvement in
seepage time, which can be used as an alternative material in the back of
drainpipes to prevent erosion. Seepage time of crumb rubber in the back of weep
holes was compared with conventional geocomposite material.
A PRELIMINARY COMPARATIVE STUDY OF SEEPAGE BEHAVIOUR BEHIND
RETAINING WALLS WITH CRUMB RUBBER AND GEOCOMPOSITE
183
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Editor received the manuscript: 18.11.2019
