Compacted red soil-bentonite liners: effect of compactive effort, wet-dry cycles and chemical contamination
摘要
The ever increasing environmental concerns surrounding the waste containment underscore the need for sustainable liner materials with low hydraulic conductivity that can withstand the environmental stresses. Red soil, a locally available kaolinitic soil in India, appears promising as a liner material when amended with bentonite, but its long-term performance under wet-dry cycling and chemical exposure remains largely unexplored. This study investigates the volume change and hydraulic behaviour of red soil-bentonite mixtures (RBMs) with 10%, 20%, and 30% bentonite, compacted to standard Proctor and modified Proctor maximum dry unit weights at their optimum moisture contents, and subjected to wet-dry cycles and chemical contamination. The laboratory test results show that the RBMs compacted with the standard Proctor compactive effort exhibited severe structural degradation, with hydraulic conductivity increasing up to four orders of magnitude (from ~ 10−8 cm/s to ~ 10−4 cm/s) after repeated wet-dry cycles. In contrast, the mixtures compacted with the modified Proctor compactive effort maintained the hydraulic conductivities within the design limit (≤ 1 × 10−7 cm/s), even after five wet-dry cycles and exposure to 0.4 M NaCl and CaCl2 solutions. The microstructural analyses using the Mercury Intrusion Porosimetry (MIP) and scanning electron microscopy (SEM) revealed the changes in pore size distribution and soil fabric, explaining variations in hydraulic and volumetric responses under the environmental stresses. These findings suggest that the red soil-bentonite mixtures, particularly those compacted to higher dry unit weights, offer durable and efficient performance as liner materials for waste containment applications.