The influence of amendments on the volumetric shrinkage and integrity of compacted clay soils used in landfill liners

Abstract

Clay liners remain an important component of composite liners used in landfill construction. Because their hydraulic integrity is frequently lost due to desiccation cracking, either during construction or shortly thereafter. The present study was initiated to evaluate the effects of common soil additives including lime, cement, and sand on the shrinkage and hydraulic conductivity of compacted clay soils commonly used in clay liner construction. Three soils having predominant clay minerals of smectite, illite and kaolinite were amended with varying amounts of lime, cement or sand; compacted using the Harvard miniature compactor; and the volumetric shrinkage was measured on the compacted samples. Additional samples of each treated soil were compacted according to ASTM 698 and used for measurement of the hydraulic conductivity. The results show that the majority of shrinkage occurs when the samples were dried to 25 °C with little additional shrinkage at temperatures up to 105 °C. The amendments of either 4% lime or 40 to 50% sand resulted in reduced shrinkage and increased hydraulic conductivity. The addition of 3% cement reduced shrinkage by up to 50% and simultaneously reduced hydraulic conductivity by 2 orders of magnitude. Thus, amendment of clay soils having a high shrink-swell potential with Type I Portland cement has the greatest poetential for field application as an amendment to help maintain the integrity and improve the long term performance of compacted clay liners.