Sustainability of Slurry Cutoff Walls in the Zone of Fluctuating Water Table

Kenneth Kniss '05

The purpose of this research was to investigate the effects of wetting and drying cycles associated with the fluctuating water table on slurry walls. To accomplish this purpose a sand-bentonite slurry mix, typical of those used in the field, was produced in the laboratory. The materials used in the mix were analyzed by x-ray diffraction, grain size distribution, marsh viscometer and mud density tests. After completing an investigation of the soil composition, seven samples were consolidated and hydraulic conductivity tests were performed using a flexible-wall permeameter. The saturated hydraulic conductivity was measured before drying the specimens. Samples were dried in three ways: pushing air through the sample using a pressure differential, removing the sample from the triaxial cell and allowing it to air-dry, and removing the sample from the triaxial cell and allowing it to sun dry. The air-drying and sun drying were much more aggressive techniques that yielded lower saturation and corresponding water contents. After drying, the samples were resaturated in the flexiblewall permeameters and the hydraulic conductivity testing was continued. The results suggest that small changes in saturation led to a decrease in permeability while large changes in saturation caused the permeability of the samples to increase up to 1.7 times its original value. Even after 2 or 3 cycles, the hydraulic conductivity of the soil did not experience a significant increase most likely because of the nature of the sand-bentonite slurry mix. Further research is recommended regarding the effect of the fluctuating water table on the permeability of slurry walls. Specifically, further investigation should include by applying more cycles to the samples, varying the effective stress on the samples and mimicking the drying process of an actual slurry wall more accurately.