experimental and fem analysis of the geotextile geotubeigs/ldh/conf/2010/articles/084.pdf ·...
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Experimental and FEM Analysis of the Geotextile Geotube
Das, N.K. Mandal, J.N. Mandal, T.1
Postgraduate Student Professer Under Graduate Student
e-mail: [email protected] e-mail: [email protected] e-mail: [email protected]
Department of Civil Engineering, Indian Institute of Technology, Bombay1Department of Civil Engineering, Datta Meghe College of Engineering, Mumbai
ABSTRACT
The present paper addresses the performance of a hanging bag test for dewatering of slurry sludge at Powai Lake,
Mumbai, India. The hanging bag and working platform were fabricated at the geosynthetics testing laboratory at
IIT Bombay. The properties of soil and geotextile geotube are reported. Based on the hanging bag test, the flow
rate of slurry material and water level are recorded at a specific time period. The finite element method (FEM)
analysis using PLAXIS version 8.2 was used for the analysis of the geotextile geotube. The test results show that
proper selection of geotube and filling material is very important at the site for the project.
Indian Geotechnical Conference – 2010, GEOtrendz
December 16–18, 2010
IGS Mumbai Chapter & IIT Bombay
1. INTRODUCTION
The concept of geotube is not new. Many people have been
used jutebag filled with sand to protect the dam from
flooding. Geotube can be used for shore protection, erosion
control, dewatering municipal sewage sludge and drinking
water treatment plant, pulp and paper mill, aquiculture and
agricultural ponds. This system is not expensive. It is easy
to treat sludge /slurry. Koerner and Koerner(2006 & 2010),
Leshchinsky et al. (1996), Pilarczyk (2000) and Heibaum
(2010) have been carried out various works on geotube. In
this paper the geotube and frame have been fabricated and
typical test have been conducted and the result are
documented. Then FEM on geotextile geotube is also
reported.
2. PROPERTIES OF SOIL AND GEOTEXTILES
The properties of the powai lake soil are : water content
= 41% , specific gravity = 2.74 , liquid limit= 53.38%,
plastic limit= 30.78% , plasticity index=22.59, optimum
moisture content = 27.37% and dry density = 18.56 kN/
m3.
The properties of the woven polyester multifilament
geotextile are: mass=338 gm/m2, thickness = 0.0975 mm,
wide width tensile strength = 136 x 48 kN/m, strain = 13 x
8 %, trapezoidal tear = 0.75 x 0.38 kN, puncture strength
= 0.95 kN, permittivity = 0.0224 s-1.
3. HANGING BAG TEST
The apparatus for conducting test are fabricated at
geosynthetics testing laboratory at IIT Bombay and the size
of large geotextile bag is also fabricated by sewing the
geotextile at the bottom and its side as shown in the
Figure 1.
The procedure adopted for the hanging bag test in this
study is as per the GRI-GT14(2004) . Test is conducted in
the following manner:
Fig. 1: Hanging Bag Test Apparatus
1. Level the hanging bag test set up such that proper
alignment is ensured.
2. The wet geotextile bag is attached to the hanging
bag test set up by the way of the flange system
consisting of 8 metal bolts attached at the top of
hanging bag test set up.
3. Preparation of slurry involves water to solid ratio
(w/s) to be equal to 3.0. Mix the soil material with
a stirrer to obtain the slurry of the uniform
consistency adding alum as a coagulant at a dose
of 133 ppm as shown in the Figure 2.
340 N.K. Das, J.N. Mandal and T. Mandal
4. A stainless steel pan of dimension 175 mm deep
and 60 cm in diameter is placed under the bag to
collect the effluent water and some fine sediments
as shown in the Figures 3 and 4.
Fig. 2: Coagulant is Added in the Slurry
Fig. 3: Collection of the Effluent Water and Fine Sediments at
the Beginning of the Test
Fig. 4: Collection of the Effluent Water and Fine Sediments at
the End of the Test
5. Record the time for which the water level drops
by 7.5 cm. Continue to record the time for every
7.5cm increments as the water level in the bag
drops from its initial state to a height of 72 cm
until water stops draining from the geotextile bag.
6. Collect the sediments passing the geotextile fabric
from the stainless steel pan at the base of the
hanging bag during the entire test and the grain
size analysis is done.
7. Filter the water at time, 1 min., 10 min, 30 min
are collected in a sealed bottle so that one can
check on dewatering quality through the geotextile
fabric. The dewatering of sediments or dredged
material from the geotextile bag is also collected,
for environmental tests. The observations for
black and clean water are compared before and
after the test are shown in the Figure 5.
Fig. 5: Sample Collected (a) Before and (b) After the Test
Fig. 6: Formation of Filter Cake Inside the Geotube
8. Cut the geotextile bag so as to examine the filter
cake inside the geotextile bag as shown in the
Figure 6.A representative sample from the
dewatered soil material that is retained inside the
bag is collected for the determination of moisture
content and density in the laboratory.
4. RESULT AND DISCUSSION
Table 1.shows the test result of hanging bag test with woven
polyester mutifilament geotextile with powai lake slurry.
Table 1: Test Result of Hanging Bag
Water
Level
Drop,cm
te,
min
ti,
min
ti’,
min
tf,
min
Flow
Rate,
cm3/s
7.5 2.24 –7.26 0 – –
15 9.30 –0.20 7.06 7.06 14.66
22.5 23.29 13.79 21.29 14.2 7.27
30 41.10 31.6 39.1 17.8 5.81
37.5 77.20 67.7 75.2 36.1 2.86
45 138.3 128.8 136.3 61.1 1.69
52.5 221.5 212.0 219.5 83.2 1.24
60 340.4 330.9 338.4 118 0.87
72 1060 1050 1058 712. 0.14
Experimental and FEM Analysis of the Geotextile Geotube 341
Where, t0 = time to fill the bag=9.50 min. ,t
e =elapsed
time , ti =t
e- t
0 = initialized time, t
i’ = modified initialized
time and tf = incremental time.
Figure 7 shows the relationship between the flow rate
and water level from the hanging bag test.
0
2
4
6
8
10
12
14
16
0 20 40 60 80
flo
w r
ate
(cm
3/s
ec.)
water level drop(cm)
Fig. 7: Relationship Between Flow Rate and
Water Level Drop
Fig. 7 Relationship between the flow rate and water
level Depth of the slurry is decreasing up to 72 cm from
the intial state of slurry. As the soil has the high plasticity
index, dense filter cake is formed on the inside of the
geotextile geotube. As a result the dewatering slow down
.Therefore the flow rate is not high. Sometimes, coagulant
is added with the slurry to obtain better performance of
the dewatering of the geotube.
The hanging bag test is very much useful for the
proper selection and function of geotube for dewatering
flow tare with respect to time. The apparent opening size
and permittivity of the geotextile is not only the parameter
but hanging bag test is also mandatory for the design of
geotube towards the designers and contractors. The large
hanging bag test can simulate the field test. Prior to the
successful construction, at least one hanging bag geotextile
test is compulsory for the quality control and quality
assurance.
5. FINITE ELEMENTAL ANALYSIS
A finite elemental analysis has also been evaluated using
PLAXIS version 8.2.The un-deformed and the deformed
mesh of hanging bag is shown in Figures 8 and 9
respectively. Figures 10 and 11 show the vertical and
vertical incremental displacement of the geotube.
From the hanging bag test results vertical displacement
of geotube is matching with the result obtained from the
finite element method.
Fig. 8: Undeformed Mesh of Geotube
Fig. 9: Deformed Mesh of Geotube
Fig. 10: Vertical Displacement as Obtained by Finite
Element Analysis
Fig. 11: Vertical Incremental Displacement as Obtained by
Finite Element Analysis
342 N.K. Das, J.N. Mandal and T. Mandal
6. CONCLUSION
The hanging bag test gives the confidence for the selection
of the proper kind of geotextile for dewatering and shoreline
protection .The discharge flow rate is very important
parameter .The test can give an idea for the correct choice
of geotextile geotube based on site filled material. The
geotube test does not rely on the apparent opening size.
The finite element analysis show the stress concentration
at bottom of the geotube.
ACKNOWLEDGEMENT
The geotextile supplied by the Techfab India Private
Limited, Mumbai is greatly acknowledged.
REFERENCES
Broere, W. and Brinkgreve R.(2004). Plaxis manual,
Plaxis.
GRI-GT 14 (2004). Standard test method for hangning bag
test for field assesment of fabrics used for geotextile
tubes and containers, GSI, Folsom, Pennsylvania.
Heibaum, M. (2010). Tests on geosynthetics used in
waterways, 9 th international conference on
geosynthetics, Guaruja, Brazil, 3, 1197-1200.
Koerner ,G .R., and Koerner ,R.M. (2006). Geotextile tube
assessment using a hanging bag test. Geotextile and
Geomembranes, 24, 129-137.
Koerner ,G .R. and Koerner, R.M. (2010). Performance
test for the selection of fabric and additives when used
as a geotextile bag, containers and tubes, Geotechnical
testing journal, 3, 1-7.
Leshchinsky, D., Leshchinsky, O., Ling,H.I. and Gilbert,
D.A. (1996). Geosynthetic tubes for confining
pressurized slurr ies. Journal of geotechnical
engineering, ASCE, 122(8), 682–690.
Pilarczyk, K.W. (2000). Geosynthetic and geosystem in
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