Effects of desiccation cracking on the performance of compacted soil-bentonite liners
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Compacted liners for waste containment facilities are typically constructed in compacted lifts of approximately 6 inch thickness. Before placement of a subsequent lift, the previous lift is exposed to the ambient conditions, causing desiccation cracks to form. Since these desiccation effects are not represented in preliminary tests conducted in the laboratory, the results obtained are poor indicators of the performance of liners in the field. In this research, the effect desiccation cracking has on the performance of field compacted soil-bentonite liners is investigated. To simulate field compaction process, a large scale compaction device was developed. The large scale testing apparatus was capable of providing the high energy kneading effect that is used in the field. Samples were prepared at various molding water contents and allowed to dry to various degrees of exposure. Water was allowed to infiltrate, and outflow was measured. The results of this study showed that the cracks formed were wider with increase in both molding water content and degree of exposure. Measurement of soil swelling was made independently so that a correction can be applied to the infiltration rates. The initial hydraulic conductivities were lower for samples compacted at lower molding water contents. The samples with the same water content but with higher degrees of exposure showed higher initial hydraulic conductivities compared to the samples at lower exposure. However, the saturated hydraulic conductivities were lower for samples compacted at higher molding water contents. The time for the outflow to stop increased with increase in both molding water content and degree of exposure. The swelling of the soil-bentonite liner increased with both increase in the molding water contents and degree of exposure.