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: nrjkmr.das@gmail.com e-mail: cejnm@civil.iitb.ac.in e-mail: tirupanm@gmail.com

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

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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

hydraulic and coastal engineering. A.A. Balkema

Publisher, Rotterdam, The Netherlands.