Hydraulic Stability of Fly Ash-Bentonite Mixtures in Landfill Containment System

This study aimed to examine the performance of fly ash mixed materials with bentonite binder (FAB) as a recent low-cost containment system to withstand leachate infiltration. The mixture of fly ash with clay (bentonite) can increase the strength of stability and strengthen cohesion bonds between molecules. Direct shear, falling head, Atterberg limit and specific gravity test have been conducted as a preliminary study to determine the precise mixture composition of fly ash-bentonite (FAB) landfill liners. Some bentonite composition: 0% (FAB0), 15% (FAB15), 20% (FAB20), 25% (FAB25) and 25% – cured with NH4Cl (FAB25s) for 24 hours, which mixed with fly ash, showed the value of shear stability at normal stress reaching 9.5 kNm-2, 15.48 kNm-2, 45.06 kNm-2, 46.26 kNm-2 and 13.67 kNm-2, respectively. It showed that the greater the content of bentonite in the mixture, the higher the shear stress produced. Curing with saline solution can reduce the shear stress of the FAB mixture. The safety test results using Geoslope/W® show that the addition of bentonite will increase bonding between particles, bearing capacity, and shear strength of the material. The largest safety factor of 1.674 obtained from FAB20 material meets the safety standard for short-term slope stability. The use of fly ash material with bentonite is expected to be an alternative landfill liner material.