A study on mechanisms controlling the hydraulic conductivity of zeolite-bentonite and sand-bentonite mixtures

Engineered landfill liners are used for the containment of the municipal wastes and hazardous materials. They are usually composed of compacted clayey soils and synthetic membranes. Hydraulic conductivity is the major specification for liners beneath the waste. The addition of relatively small amounts of bentonite permitted sand bentonite mixtures (SBMs) to have a required hydraulic conductivity. Similarly, zeolite bentonite mixtures were also proposed for use of a liner. Several researchers investigated zeolite bentonite mixtures (ZBMs) in terms of preliminary analysis of hydraulic conductivity. It is concluded that ZBMs had higher hydraulic conductivities when compared to SBMs even for relatively higher bentonite contents. This dissertation deeply investigated the hydraulic conductivity behavior of ZBMs and possible reasons causing ZBMs to have higher hydraulic conductivities than SBMs. The findings of SBMs and ZBMs were compared and discussed. A laboratory investigation on the mechanisms controlling the hydraulic conductivity of SBMs and ZBMs has been undertaken. Compaction and hydraulic conductivity characteristics were established. The influence of compaction water content on the hydraulic conductivity of SBMs and ZBMs was comprehensively studied. In addition, water content distribution of components, void ratio of bentonite and degree of saturation to bentonite in a binary mixture were investigated. Finally, a finite element analysis was conducted in order to clarify the influence of porous grains, simulating zeolite, on the hydraulic conductivity of a binary mixture. The results are presented and analyzed and recommendations for future studies are made. Keywords: Zeolite bentonite mixtures, sand bentonite mixtures, hydraulic conductivity, water content distribution, bentonite void ratio, finite element method.