• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.1264-1273
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• 2010

Soil-bentonite cutoff walls are widely recognized to be the effective barrier for containment of wastes and groundwater. Bentonite cake is usually found remaining on the trench surface due to the use of bentonite slurry during the excavation for the cutoff wall construction. Defects also inevitably take place due to the inappropriate construction procedures or improperly mixed soil-bentonite backfill. The defects include insufficient keys and windows in the soilbentonite cutoff wall. In this study, the performance of the soil-bentonite cutoff wall is evaluated based on the flow rates through the wall. Three-dimensional numerical models were applied to simulate the groundwater flow through the soil-bentonite cutoff walls of typical geometries with consideration of the defects and bentonite cake. Results of the simulations showed that the bentonite cake has no effect in the insufficient key cases. In the keyed wall cases, the bentonite cake with very low hydraulic conductivity significantly impedes the flow of groundwater through the wall. The presence of the bentonite cake not only compromises the window defect but also renders the wall construction more effective in blocking the groundwater flow. These findings show the significance of the bentonite cake in a soil-bentonite cutoff wall construction.

• Journal of the Korean Geotechnical Society
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• v.29 no.6
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• pp.5-17
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• 2013

Slug tests can be adopted to estimate hydraulic conductivity of the slurry trench wall backfill for its abilities to reflect the in-situ performance of the construction. A comprehensive three-dimensional numerical model is developed to simulate the slug test in a slurry trench wall considering the presence of bentonite cake on the interface boundaries between the wall and the surrounding soil formation. Influential factors such as wall width (i.e., proximity of wall boundary), well deviation, vertical position of well intake section, compressibility of wall backfill, etc. are taken into account in the model. A series of simulation results are examined to evaluate the bentonite cake effect in analyzing practical slug test results in the slurry trench wall. The results show that the modified line-fitting method can be used without any correction factor for the slug test in the slurry trench wall with the presence of bentonite cake. A case study is reanalyzed with the assumption of existing bentonite cake. The results are compared with the previously reported results by the approaches assuming no bentonite cake (constant-head boundary) or upper-bound solution (no-flux boundary). The case study demonstrates the bentonite cake effect and the validity of the modified line-fitting method in the estimation of the hydraulic conductivity of the slurry wall backfill.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.498-507
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• 2008

The mixture of bentonite powder and water is generally used to maintain the stability of excavation surface during the construction of vertical cutoff walls. The filter cake on the sidewall surface is the result of filtration of slurry into the adjacent soil formation. The filter cake is believed to have a very low hydraulic conductivity compared to that of the cutoff wall. This paper evaluates hydraulic conductivities of bentonite filter cakes set up with three types of bentonites under various pressure levels. A modified fluid loss test was employed in this experiment. Theory of filtration process was reviewed to explain the procedure in the present experiment. Hydraulic conductivity of the filter cakes with consideration of the filter medium resistance was evaluated. The results of the experiment with two calculation methods and discussion are presented to show the efficiency of the modified fluid loss test.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1502-1511
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• 2008

The mixture of bentonite powder and water is generally used to maintain the stability of excavation surface during the construction of vertical cutoff walls. The filter cake on the sidewall surface is the result of filtration of slurry into the adjacent soil formation. The filter cake is believed to have a very low hydraulic conductivity compared to that of the cutoff wall. This paper evaluates hydraulic conductivities of bentonite filter cakes set up with three types of bentonites under various pressure levels. A modified fluid loss test was employed in this experiment. Theory of filtration process was reviewed to explain the procedure in the present experiment. Hydraulic conductivity of the filter cakes with consideration of the filter medium resistance was evaluated. The results of the experiment with two calculation methods and discussion are presented to show the efficiency of the modified fluid loss test.

• Journal of the Korean Geotechnical Society
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• v.27 no.2
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• pp.53-62
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• 2011

During the construction of vertical cutoff walls, filtration of bentonite slurry into the adjacent soil formation fabricates a layer of bentonite filter cake on the wall surface. The bentonite filter cake possesses much lower hydraulic conductivity compared to that of backfill materials in the cutoff wall. Hydraulic conductivity of bentonite filter cakes formed with three different types of bentonites has been measured by performing the modified fluid loss test under various pressure levels. Three different mixture ratios, 4, 6, and 8%, were selected for fabricating bentonite filter cakes to represent common field conditions. Two analysis methods for interpreting the experimental data from the modified fluid loss tests were employed to estimate hydraulic conductivity of the bentonite cakes. The range of hydraulic conductivities of the three bentonite cakes is between $2.15{\times}10^{-11}\;m/s$ and $2.88{\times}10^{-10}\;m/s$ which is 1 to 2.7 orders of magnitude lower than that of the design cutoff wall backfill. The stress distribution and thickness of the bentonite cakes were also evaluated in this paper.

• Asian-Australasian Journal of Animal Sciences
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• v.8 no.3
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• pp.249-254
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• 1995

The effects of bentonite (B) on rumen protozoal population and rumen fluid characteristics of sheep fed palm kernel cake (PKC) were studied for a period of 21 days. Two groups, each comprising two sheep were fed either PKC or PKC + B ad libitum A third group was left at pasture. Rumen fluid was sampled through a rumen cannula three times daily from all animals. Palm kernel cake contained 16% crude protein, 1 % crude fat and high amounts of copper, zinc, iron and manganese. Protozoal population in the rumen fluid decreased significantly (p < 0.05) after the onset of feeding PKC or PKC + B. However, sheep given bentonite supplementation at 2% of the dietary dry matter, maintained higher protozoal densities ($15{\times}10^4/ml$) when compared to animals fed only PKC ($8{\times}10^4/ml$). With both diets, the protozoa were mainly of the small entodinia species. Animals at pasture had higher protozoal population ($47{\times}10^4/ml$) with varying species of entodiniomorphids and holotrichs. Rumen fluid pH and ammonia concentration was significantly (p < 0.05) higher in animals at pasture compared to animals fed PKC or PKC + B. Volatile fatty acid concentration was significantly (p < 0.05) lower in animals fed PKC when compared to animals at pasture. There was a shift in fermentation pattern in animals fed PKC or PKC + B towards a lower acetate; and higher propionate, isovalerate and valerate. Studies in vitro also showed the positive effect of bentonite on protozoal numbers.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.239-248
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• 2002

Bentonite slurries in a slurry wall construction must fulfill a stabilizing function by forming impermeable membrane (surface cake and penetrated cake) on the excavated soil faces. Thus problems are occurring in practice for the construction of diaphram walls and cut-off walls with a low permeability for wastes disposal areas in some deep excavations or different grounds. In this paper, the fundamental mechanics of fluid loss and filter cake formation in various soil beds are investigated using large scale laboratory apparatus. The sealing efficiency of filter cake from the large scale tests and the significance of fluid loss in a slurry trench are utilized for practical situation as a recommended design procedure.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.407-426
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• 2008

The bentonite slurry has been used as the stabilize suspension for wet process bored pile construction in Thailand. The bentonite suspension has benefit on filtration in the sand layer, but it creates thick cake film along pile shaft and loose sedimentation at pile toe. The base grouting technique was widely used to rectify the soft base or loose sedimentation problem of bored pile. The base grouting technique was not increased only end bearing capacity, but was also more increase in skin friction capacity of the bored piles. The comprehensive researches on base grouting was carried out by installing PVC casing inside the shaft to allow the drilling through the pile base in order to collect the soil sample below the pile tip. The polymer based slurry recently was used to replace the bentonite slurry to overcome the thick cake film along pile shaft as well as loose sedimentation at pile toe. The extent research on polymer slurry by physical model was performed to verify the real behavior of polymer. The appropriate mixing ratio of polymer was proposed. The design skin friction coefficient, $\beta$ and end bearing coefficient, Nq, for sand layer base on fully instrumented tested pile were proposed. The application on remedial of the lose capacity bored pile with large displacement in Bangladesh was proposed and discussed.

• Membrane Journal
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• v.18 no.1
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• pp.53-64
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• 2008

Fouling behavior of polyethylene capillary membranes was examined by measuring the flux of bentonite colloidal suspensions through the cross flow micro filtration. The membrane fouling was due to the three mechanisms: the cake formation on the membrane surface, the standard pore blocking and the complete pore blocking by particles. These mechanisms were simultaneously responsible for the membrane fouling, being significantly governed by the cake filtration. In the total fouling at $1.0kg/cm^2$ TMP condition, the complete blocking was 3.36%, the standard blocking 3.18% and the cake filtration 96.05%. For 1000 ppm feed solution, the complete blocking was 1.71% compared with the standard blocking of 1.90% and the cake filtration of 96.39%. And 96.14% of the total fouling was generated at the initial period of filtration. The cake filtration effect was larger on $0.34{\mu}m$ pore membrane than on $0.24{\mu}m$ pore membrane. With the increase in cross flow velocity, the component fouling decreased by 10.20%, and the ratio of pore blocking to total fouling increased.

• KCI Concrete Journal
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• v.14 no.4
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• pp.151-159
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• 2002

This study investigates experimentally the optimum mix proportion and design factors of the stabilizing liquid used for excavation of the massive and deep slurry wall in LNG in-ground tank before pouring concrete. Considering those site conditions, the stabilizing liquid used for excavation of slurry wall has to be satisfied with some requirements including specific gravity, fluid loss, cake thickness, funnel viscosity and sand content in order to construct the safe and qualified slurry wall. For this purpose, we select materials including bentonite, polymer and dispersion agent. After performing many tests for materials and mix design process, we propose the optimum mix proportion that the upper limit ratio of bentonite is $2.0\%$, polymer is $0.1\%$ considering the funnel viscosity and dispersion agent is $0.05\%$considering the fluid loss of the stabilizing liquid. Also, we select all materials which are consisted of GTC4 as bentonite, KSTP as polymer and Bentocryl 86 as dispersion agent. Based on the results of this study, the optimum mix proportion of the stabilizing liquid is applicable to excavate the deep and massive slurry wall in LNG in-ground tank successfully.