1 ^

£ 4

\

c\

\

^

^

CVN.

^

3.5.2 Initial Water Content

In the same study of confining pressure by Liao and Bhatia (2005), the water content

V increases from 100% to 400% as the maximum flow rate increases from 4 to 12 cm/min (Figure

3.32). The author concluded that the filter cake formed above the geotextile is thinner for the

slurry with higher water content and it is easier for the soil particles to pass through the geotextiles.

The conclusion is supported by final height of the soil column with a pressure of 35kPa after the

tests was 7.52, 4.45, 2.63, and 1.77cm for the specimens prepared at water contents of 100%, 200%,

300%, and 400%, respectively. v

^-—^ rf ^^ \ , fUA^3.5.3 ^CoHtent of Air Bubbles J)

In the-past, th^pHrllcfe size and its distribution were assumed to be the critical properties

which affect the filtration rate. Kakwani (1983) observed that entrapped air bubbles could also

cause significant changes in filter cake structure and adverse effects on the filtration process.

The number and size of entrapped air bubbles are evaluated in the filter cakes. In the study of

Chi (et al., 1985), the particle size of the coal samples and other variables are held constant in

order to distinguish the effects of entrapped air bubbles. The size of coal sample fractions is

classified into -80 mesh, -42 mesh, -32 mesh, and -100 +200 mesh filter. These

"surface-volume mean particle sizes" (XP°rl), which is the diameter of a sphere having the same

surface-to-volume ratio as the particle, for four samples are 41.8 urn, 81.6 urn, 120.1 urn and

154.4ujn, respectively.

The experimental results give a visual image of the entrapped air bubbles inside the filter

cake shown in Figure 3.32. The air bubbles are easily recognizable under the microscope, and

it is black in circles with a white spot at the center of the two-dimensional cake sections (Chi et

al, 1985).

85

1

and cake permeability decrease from a factor of 2 to nearly 4. When the volume percentage of

air bubbles increases from 0.5% to 3%, the filtration flux and cake permeability decrease by a

factor of 2 to 2.5. For dewatered cakes, the maximum percentage of entrapped air bubbles is

less than 2% with a narrow size distribution range from 150 to 240 um of air bubbles of

dewatered cake pore volume. The distinction of the volume percent of air bubbles in 'aerated',

'normal' and 'deaerated' dewatered cakes ranges from 0.4% to 2.0%, 0.4% to 2.0% and 0.6% to

0.9%, respectively, and are not as easily found as those in comparable filter cakes is 1.0% to

4.3%, 1.2% to 5.2% and 0.4% to 1.5% (Chi et al., 1985).

The size and volume percentage of air bubbles increase from the bottom to the top for

each filter cake. The increase is explained because air bubbles tend to rise in the filter cake

due to the buoyant force in the early stage of cake formation. Bigger air bubbles have larger

buoyant forces. Therefore, air bubbles migrate upward and are trapped in the upper layer of

the filter cake. The mean size distribution of air bubbles is different in dewatered cakes than in

filter cakes and dewatered cakes tend to have a more uniform size distribution. The rate of

filtration and tjredewatering are both adversely affected by the air bubbles in the filter cake

which is caused by the lack of connectedness with pores in cake matrix.

/

89

Chapter 4 GEOTEXTILE TUBE STATE OF THE ART

4.1 Introduction

This section discusses designing geotextile tubes and testing that has been used to

evaluate the filtration behavior between geotextiles and soils.

4.2 Behavior of Geotextile Tubes

The parametric study done by Leshchinsky (et al., 1996) was used to gain a better \ a

(runderstanding of the effect of different design parameters. In this study, the relationship among

ultimate tensile force, the height of the tube, and the pumping pressure will be discussed.

7?4.2.1 Ultimate Tension

Figure 4>U$nows the effects of the specified tensile force in the circumferential direction / / J

of the geotextile tube. When the cross section is a perfect circle, with diameter equal to

D YM1 = 2-9 m (9.5 ft), the required tensile force and pumping pressure increase toward

infinity. However, when T is as low as 14.6 kN/m (1,000 Ib/ft), the height is only 1.8 m.

Thus H is 63% of the maximum theoretical height, D. By increasing T to 87.9 kN/m

(6,023 Ib/ft), the tube height would increase to 2.6 m which is 89% of D. The cross sectional

area has little influence, while the height changes. This information gives clear design

implications if a certain volume of slurry is needed (Leshchinsky et al., 1996).

90

* Circumference of tube, L = 9 [m]* No outside water

* ' slnsy/ 'water — 1.2

* No safety factors on geosynthetic strength

= 875.0 kN/m

— -0 98Wp = 593.4 kPa* o

Area -6.66 m2

H = 2.9m

= 87.5 kN/m j

= 0.83p = 52.4 kPa1 o

Area= 6.51m2

= 2.6m

14.6 kN/m

w= 0-5 0p = 4.8kPa1 0

Area =5.56 m2

H = 1.8m

Figure 4.1: Effects of TU|t on Geometry of Tube (Leshchinsky et al., 1996).

4.2.2 Height

Figure 4.2 illustrates the influence of the designed height H of the geotextile tube^, If \ //

the desired tube height is 0.9 m, about 31 % of D, the required pumping pressure is nearly zero.

The required circumferential force is 2.6 kN/m (178 Ib/ft). However, if the desired tube height

is 2.7 m, about 94% of D, the required pumping pressure is about 122.8 kPa (17.8 psi). The

required circumferential force is approximately 190 kN/m (13,019 Ib/ft) (Leshchinsky et al.,

1996).

"After the pumping and as the slurry consolidates, experience indicates that the height

of the tube drops, while its maximum width increases very little" (Leshchinsky et al., 1996).

The dropping height of the tube can be very large, especially with fine-grained soil. An

^/

91

H = Initial height of tub eA H 0 = Change (drop) m height of tube

/T ) = Wtial sl«ny tatit Wii^tt / X,) * <$$ ..J' 0 •• '•'•

1.1 L2 U 14 IS \& 1.7

( «sofl/ 'w/f

Figure 4.3: Drop in Height of Tube as Function of Density of Soil (Leshchinsky et al.,

1996).

4.2.3 Pumping Pressure

Figure 4.4 shows the effects of the pumping pressure of the geotexifile tube. If the

pumping pressure (po) is 34.5 kPa (5 psi), the tube is 2.5 m in height and 61.7 kN/m (4228 Ib/ft)

in circumferential force. However, if the pumping pressure increases to 103.5 kPa (15 psi), the

Jlmjfe Z7 m ittube becorare J.I m in height, and the circumferential force increases sharply to 462.0 kN/m

93

(31,6551b/ft). From the observations of Leshchinsky (et al., 1996), pumpingxp'ressure beyond

35 kPa (5 psi) would not increase the tube height significantly, but the/gfrengthajbplied to the

geotextile increases exponentially. Typically, a pumping dredge line is about 300 kPa (44 psi)

or more. Strict field control is needed since the pumping pressure can build up a force which

can rupture the geotextile.

* Circumference of tube, L= 9 [in]* No outside water

* ' slurry/ 'Wafer — 1 . 2

* No safety factors on geo synthetic strength

i_p5_=J03.5_kPa

Tljlf = 462.0kN/m

w=°- 9 0H = 2.7m

Area = 6.57rnz

H = 2.5mArea= 6.45m2

p = 6.9 kPa*• o

= 18.1 kN/m

~= 0.55

: 2.0mArea= 5.7r5 m2

Figure 4.4: Effect of po on Geometry of Tube (Leshchinsky et al., 1996).

Figure 4.4 and Figure 4.5 illustrate the relationship between the height of the tube and

the pumping pressure. It can be seen that p0 has the most significant influence on height at low

rC\. Therefore, as the pressure increases, its effect on H become^in^ignificant. The

relationship approaches the asymptote of H = D only when p0 increases/o infinity (Leshchinsky

et al., 1996).

94

Figure 4.6 shows the effectSyof pumping pressure on both T and Taxja|. It is shown that

as po increases, the difference offlie values between/the circumferential force and the axial force

become larger. The usage oranisotropic strength/can be economical when selecting

geotextiles with significantly different tensile forces T and Taxja|. Two geotextiles transfer

force through seams. Therefore, seam strength and seam efficiency are important factors-^__ . ->(Leshchinsky et al., 1996).

Figure 4.7 depicts the maximum theoretical height and minimum feasible height of a

tube with a circumference L. The maximum theoretical height, Hmax, is equal to the diameter

of a tube with a circular cross section. The minimum feasible height, Hmjn, corresponds to a

case where the pumping pressure is about zero. This figure also indicates the range of feasible

heights for given circumferences.

16

10 15 20 25 30 35 40 45 50

Circumference of Tube, L [m]

Figure 4.7: Extreme Values of Height of Tubes (Leshchinsky et al., 1996).

96

4.3 Design of Geotextile Throes \I (—•>

i fWith its environmental iend/y characteristics, geotextile tubes provide a solution to

\ / / / *problems in environmentally^se&smve areas. By sevym-g-^everal geotextiles together in the ,

^/^Y^shape of a tube, it could retain a large amount o\ materials^ith high water content. /They/are

highly permeable nattfre and their ability to be stacked are the two main advantages of geotextile,

when compared to settling ponds within a limited construction site.

There are numerous articles discussing the formulation for the tensile force of the

geotextile tube, but most are incomplete. Leshchinsky (et al., 1996) proposed an overview of a

complete formulation which indicated tensile force along the circumference and the geometry of

the cross-section of the geotextile tube. In his study, the design of geotextile tubes for strength,

durability, and permeability are provided. The design of geotextile tubes is based on the force

equilibrium of the geotextile. The governing assumptions for the formulation are as follow:

1. The tube is long and the cross-section is perpendicular to the surface. Thus the pressure loss

.• t

in the filling process, while draining is ignored, and the pumping pressure is used for the

analysis.

2. The geotextile of the tube is thin, flexible, and weightless.

3. A hydrostatic state of stresses occurs in the geotextile tube.

4. No shear stresses generate between the slurry and the geotextile tube.

4.3.1 Strength Design

Leshchinsky (et al., 1996) presented a design method based on the force equilibrium along

the circumferential direction of the geotextile. The geotextile tube is assumed to be surrounded

by air and filled with one type of slurry. In Figure 4.8, the cross section is symmetrical with a

maximum height (H) at the centerline, maximum width (W), and a flat base that is in contact with

97

woven geotextiles, the safety factor of two is recommended (Leshchinsky et al., 1996). The

defective seam may render geotextile tubes ineffective, especially for clayey slurries. Seam

efficiency is defined:

E (%) = Tseam x 100 (Equation 4. 2)Tgeotextile

Where,

= wide-width seam strength,

= wide-width geotextile strength.

4.3.3 Durability

4.3.3.1 Installation Damage

A$6I the installation of a geotextile tube, the high pressure of pumping fine-grained

material may lead to a rupture of the geotextile. Pumping pressures beyond 35 kPa (5 psi)

will increase the stress on the geotextile exponentially. A factor of safety is needed for

pumping pressure uncertainties, flaws in the geotextile material, and poor construction control

by the contractor. Excessive pumping pressure may cause local rupture adjacent to the seam

of the geotextile (Leshchinsky et al., 1996).

4.3.3.2 Chemical and Biological Degradation

Typically, geotextiles are inert to the slurry. The specified test in ASTM D 5322

(Standard Practice for Immersion Procedures for Evaluating the Chemical Resistance of

Geosynthetics to Liquids) can be used to verify the chemical damage cause by the slurry.

Furthermore, since the geotextile tubes might be exposed to the sun every day, the degradation

100

I/I\J

by ultraviolent radiation is\vXso another consideration. The specified test is ASTM D 4355

(Standard Test Methocfior Deterioration of Geotextiles for Exposure to Ultraviolet Light and

Water). Additional carbon black may be added to extend the resistance to the deterioration

f )slowly caused bjl U\/' Biological degradation is another consideration, but it is not an issue

in most cases (Leshchinsky et al., 1996).

djV/'4.3.3.3 Creep

Creep is defined as the elongation of the geotextile under constant load./ In the

dewatering application, the geotextile tube would experience a maximum force from the initial

filling process and the force decreases as the slurry consolidates. However, creep is

continuously influenced by the force within the geotextile and it might rupture the geotextile

tube. The specified test is in ASTM D 5262 (Standard Test Method for Evaluating the

Unconfined Tension Creep and Creep Rupture Behavior of Geosynthetics). Reduction factor^)

.— if applied to the use of the ultimate strength of the geotextile and this will prevent from creepi)

of the designed life of the geotextile tube. Reduction factor also depends on the type of

geotextile (Leshchinsky et al., 1996).

4.4 Testing of Geotextile Tubes

4.4.1 Lab Testing

4.4.1.1 Falling-Head Dewatering Column Tests (FHDT)

Since a hanging bag test is hard to observe and evaluate filters cake because of the

possible disturbance during operations. Therefore, a falling-head dewatering column test

101

the chamber. Then the screws on the upper plate are tightened and the air pressure is applied

promptly to the required pressure. Graduated cylinders are used to collect and measure the

volume of filtrate with elapsed time. After the test is finished, the filtration device is

disassembled. The final height of the dewatered cake is measured and the total settlement is

calculated. Finally the analyses of the dewatered cake and the filtrate are conducted. The

filtration efficiency of this test is calculated by the total suspended solids of the discharge flow

to the initial total solids of the sample. The dewatering efficiency of this test is determined

by the initial percent solids and the final average percent solids.

Pressure Gauge Pressure Itilet

Porous Holder

I ""2a

ff Sludge

Ji ^

IFiltrate Outlet

1

^^•Geo

"3— — >

rs

Upper Plate

5* Chamber

Support

Figure 4.12: Pressure Filtration Test Apparatus (Moo-Young et al., 2002).

4.4.1.3 Rapid Dewatering Test

The rapid dewatering test (RDT) is presented by the company TenCate. The primary

function of this test is to (TenCate, 2009):

• Evaluate the efficiency for different polymers

• Measure the volume of discharged fluid from the sludge.

105

through the fabric and sediment passing through in an elapsed time. It is also used toft

evaluate the properties of the dewatered infill material and to examine the nature of the filter

cake. This test method is used to predict the behavior between the in situ specific fabric and

the specific infilled material. The intent of this test is to provide design information for a

designer or contractor before approving a particular fabric for a particular site (Koerner and

Koerner, 2006).

102 cm (40")

',

^

Ho! CutEdgs X.

\nSeam vLilM N,

mm iTu

•sanm 2.5«ninK HI*^^^^^^^^^^^^

Fold

163 5mf6»T

1S2cn».(60T

SewnSeani

N

(b) (c)

Figure 4.14: (a) Hanging bag test apparatus, (b) geotextile before fabrication and (c)

after fabrication (Koerner and Koerner, 2006).

Figure 4.14 shows the apparatus used for this test. A large bag was made by sewing a

fabric along its sides and bottom to form an enclosure that will support and contain a certain

amount of saturated infill material. The volume of the bags was approximately 175 L (40

gal). The bag opening has eight evenly spaced metal grommets around its upper perimeter

and is hung from the inside of the wooden frame. A pan is placed under the container to

108

collect sediment. The moisture content of the soil within the bag and particle sizes of the soil

passing through the bag can be tested back in the laboratory.

The Procedure) fM$ hanging bag testUvas provided by Koerner and Koerner (2006).

1. The hanging bag is first soaked in to the dredged area for pre-wetting.

2. The bag is attached to the wood frame with a distance less than 8 in. from the bottom of

the bag to the pan below.

3. After the bag has started to drain free water, a pan with a 3 in. deep and 24 in. diameter

was placed-below collecting fines.

4. 10 gaflloi^of site specific material and 40 gallpn^of sue water are prepared. Then the soil

^-^ V_^/ /*~^4 material and the water are evenly mixed together. ^ / /?

5. The premixed slurry is poured into the bag as the stopwatch began. Record the time

every 3 in. the slur

6. Hang the bag until water stops draining.

7. At the end, the pan is removed and the collection was transferred to a stainless steel drying

dish. The dish is brought back to the lab to determine the dry mass of sediment.

8. Measure the mass of the bag and obtain a representative sample from the inside of the

ID &\ /'gm&xtile. Evaluate the moisture content of the sample back in the laboratory.^/w

9. Calculate the discharge flow rate with the increment of the elapsed time for a slurry level

drop of 3 in.

"No geotextile tube project should be designed without having conducted at least one

HBT under simulated site-specific conditions." (Koerner and Koerner, 2006). This test can

represent the behavior of the geotextile tube and gives the designer an opportunity to test

different flocculants and geotextiles. However, this test contains both hard working and time

109

consuming. With preparing samples, test setup, unknown dewatering periods, and data

analysis, it might take an entire day to do a single test.

4.4.2.2 Settling and Self-Weight Consolidation Column Test (SSCC)

The settling and self-weight consolidation column test was proposed by the U.S. Amy

Corps of Engineers (USAE, 1987). The purpose of this test is to determine settling velocity

(Vs) and self-weight consolidation coefficients (CF) of silty clay with different initial water

contents. In Figure 4.15, this test is conducted using an acrylic settling column with a height

of 45 cm and 10 cm in diameter (Shin and Oh, 2004).

The soil is prepared with various water contents derived from the mixing ratio of the

soil and salt water mixture. The predetermined amount of dredged silty clay is first measured

and introduced into a settling and self-weight consolidation column. A ruler is attached

vertically to the column to measure the depth from the water surface to the interface of the

water and slurry.^and to recorcTthe self-weight consolidation settling time. The initial

——— " " ' ' fSfnperature of the salt water is measured and compared to the slurry at the end of the test. \t

is difficult to estimate the preliminary settling process, so the SSCC test was performed to

estimate this process. J\\fter the preliminary settling ends, the valves are opened, while theJ L~

supernatant water is extracted from the column and continue to perform the self-weight

consolidation test?) The depth from the water surface to the interface of the self-weight/^

consolidation settlement is recorded at different times.

no

gJM* WEDGED' " tr£»/4

sutttrtr

VALVES «3« SAMPLEEXTRACTION

SCTTUNG STON£

Figure 4.15: Schematic of/Settling and self-weight consolidation column (USAE, 1987).

ou.ITuiI-2

Oh-ZHQ-UJO

ZONE SETTLING

SLOPED ZONE SETTLING VELOCITY

COMPRESS/ON SETTLING

TIME

Figure 4.16: Typical zone settling process (Shin and Oh, 2004).

From the plot in Figure 4.16, Vs can be determined by the slope of the initial portion of

the line. Regression analysis for both CF and Vs can be estimated fronvthis-test:

Furthermore, the field behavior for both CF and Vs can be predicted as discussed in section

2.3.3.

4.5 Case Study

Koerner and Koerner (2005) contrasted three case histories in which geotextile tubes were

used in three different field performances, and the results of hanging bag tests and the pressure

filtration tests were also provided. Soil properties and fabric properties are tabulated in Table

4. land Table 4.2.

112

Site No.l was located at a beach resort along the Atlantic Ocean and geotextile tubes were

constructed in September 1999. The purpose of this project is to protect the shoreline transition

between the boardwalk and the beach by using geotextile tubes. The geotextile tubes at this site

are made of woven polyester geotextile (Fabric A-l). The geotextile tubes are filled with sand

which is classified as poorly graded (SP) with high permeability. Because so much water is

emerging and expelling from the tube, sacrificial sheets of plastic, scour aprons, and anchors

were utilized to keep the water from undermining the geotextile tube in this design. The

geotextile tubes performed very well in this application resisting Hurricanes Floyd and Isabelle

within 4 years after they were built.

(a) (b)

Figure 4.18: (a) Hanging bag test and (b) Geotextile tube at site No.2 (Koerner and Koerner,

2006).

Site No. 2 was located at a marina inland from the Atlantic coastline where geotextile

tubes were placed in December 1999. ( i n this application, the silted up marina is solved by using

geotextile tubes for dewatering silts and clays in that areaA The geotextile tubes are made of

woven polypropylene geotextile (Fabric A-2) and the filling material is classified as silt with low

plasticity (ML). The authors were not satisfied with the result. In addition to the low

115

\y due to the fine-grained materials, the oily slurry makes the dewatering process even

—~vworse since it accumulates rapidly and forms the shiny filter cake inside the fabric/ A flocculant

(polyacrylamide) was added to enhance the permeability. Finally, Koerner and Koerner (2005)

concluded that the results were relatively successful even though the increasing time and expense

for adding flocculant.

(a) (b)

Figure 4.19: (a) Hanging bag test and (b) Geotextile tube at site No.3 (Koerner and Koerner,

2006).

Site No. 3 was located at an industrial site near the Great Lakes. Geotextile tubes were

placed in the summer of 2000. This project uses geotextile tubes for dewatering lagooned ash

which it is classified as well graded sandy silt (SW). Geotextile tubes are made of woven

polypropylene geotextile (Fabric B-l). Koerner and Koerner (2005) concluded that the result is

good to fair in this application even though the final moisture content did not go below 30%.

The soil at each site was tested by both hanging bag test (HBT) and pressure filtration test

(PFT) in the laboratory. The HBT has been discussed in section 4.4.2.1 and PFT is in section

4.4.1.2. In PFT, a mixture of 125 ml of 4% polymer flocculant and a surfactant mixture of 125

116

ml of 4% NaPOs were also used separately in the test to compare with water and soil alone. The

results are shown in Table 4.4 and 4.5

Table 4.3: Average HBT permeabilities for the site soils(ksoii) (Koerner and Koerner, 2005).

Fabric A-1 Fabric A-2 Fabric B-l Fabric B-2(cm/sec) (cm/sec) (cm/sec) (cm/sec)

Site 1Site 2Site3

0.30.0050.07

0.20.0020.05

0.10.0030.04

0.4

0.004

0.08

Table 4.4: Average PFT permeabilities for the site soils(Koerner and Koerner, 2005).

Fabric Fabric Fabric FabricA-l A-2 B-l B-2

(cm/sec) (cm/sec) (cm/sec) (cm/sec)

Site 1water/soil alonew/flocculantw/surfactantSite 2water/soil alonew/flocculantw/surfactantSite 3water/soil alonew/flocculantw/surfactant

2.22

2.1

0.0020.0060.001

0.090.150.08

2.212

2.2

0.0040.0070.003

0.10.140.08

2.12.12

0.0040.0050.002

0.10.130.07

2.22

2.1

0.0060.0080.005

0.20.2

0.15 7

In conclusion, Site No. 1 had the best results since the geotextile tube contained granular

beach sand because of its immediate settlement and fast drainage. However, the result in Site

/ r No. 2 was not satisfied in the field test and lab tests. )lt can be indicated jthat the material is thev <- ^

finest with the lowest permeability and the highest plasticity index. Furthermorefit generatedV_y

the thickest filter cake inside the geotextile tube. More research is needed to test similar

materials by improving the dewatering behavior of the geotextile tube.

117

Chapter 5 FURTHER RESEARCH

Geotextile tuoes have been used for dewatering dredged materials commercially for over

forty years. They have been designed by software and tested in laboratory experiments, but

more research-needed due to predictions of the geotextile tube shape being highly empirical.

I r—v ~^>|iV | Several aspects of research may be considered as follows. /

In the aspect of consolidation, theories that are related to consolidated geotextile

based on TerzagjH^Theory, such as constant rate of loading, constant rate of strain, and radial

consolidation (on/nor/zontal plane. No research has been done to study these aspects of

consolidation. Most researchers have done studies based on empirical experiments, such as the

volume reduction method and the settling and self-weight consolidation method. Even though a

problem had been proposed by Shin and Oh (2004), the volume reduction method has been

widely used commercially due to the simplified way it estimates the consolidation of a geotextile

tube. The settling and self-weight consolidation method has a better solution to predict the

shape of the tube, since this method is used for dredged materials. However, this method

requires more complicated knowledge and calculations to understand and more tests are required

with different materials to develop a general solution.

In the aspect of filtration behavior, a lot of criteria and testing can be used for determining

the filtration behavior of geotextiles. Researchers had found om that POA is a better way to

understand the filtration behavior for woven geotextiles whereas AOS is preferred for nonwoven.

Hanging bag tests are the most recommended test to have a pretty good idea of the filtration

behavior of a geotextile tube, but the disadvantage of this test is that it is a case by case study in

which the result only fits to the specific geotextile and the fine-grained soil used in the test.

More studies on the interaction between the geotextile and fine-grained are needed to set up a

J>-<

118

0'

reliability-based design for geotextile tubes.

In regards to cake formation, the critical dewatering behavior of geotextile tubes is due to

the formation of the filter cake which is built inside. Many theories related to cake filtration

have been done, such as conventional cake filtration theory and multiphase filtration theory. No

research has been done on cake filtration directly related to the behavior of geotextile tubes.

/ ( _ Frkeraids are additives which hold more particles together and increase the porosity of

the filter cake. HenceTit improves the permeability of the filter cake. Sabah and Erkan (2006)

had done a lot of studies on different filter aids. The results were affected by different filter_aids,

the amount of dosage used, and the pH condition.^ There has no study been done directly related

to the behavior of the geotextile tube with using a filter aid. Standard criteria may be developed

* —- r— /in the future. ^ AK^

In the aspect of construction, pumping pressure is the most important issue that-had been"

reported. It is known that with the increasing pumping pressure, the tension increases

exponentially and may rupture the geotextile tube. More studies are needed to set up a standard

process for determining the pumping pressure that should be used with different kinds of

s^T\d filled materials.

119