Combined Shear and Seepage Characteristics for Selecting Drainage Layer in Near Surface Hazardous Waste Disposal Facility

Several near surface disposal facilities (NSDF) and engineered landfills necessitate well designed multi-layered barrier (MLB) for minimizing the interaction of waste with the groundwater and atmosphere. These MLBs are provided below and above the wastes as liners and covers, respectively. Drainage layers in MLBs, helps to collect and divert infiltrating rain water or leachate there by reducing hydraulic head and downward seepage or infiltration rate. Improper design considerations, clogging by fines, insufficient capacity, and inadequate shear strength of aggregates used in drainage layer can cause its failure. Shear strength and seepage characteristics play a prominent role in the design of drainage layer of MLB. The objective of this study is to understand the effect of variation in particle size and relative density of aggregates on the shear strength and seepage characteristics. It was observed that with an increase in particle size, both permeability and shear strength increases. The relative density was found to significantly influence shear strength only but not permeability. The study recommends a more robust procedure for identifying appropriate aggregates in drainage layers based on combined shear strength and seepage characteristics. By considering both shear strength and seepage characteristics, a relative density of around 60% was found to be optimal for the higher sized aggregate used in drainage layer of MLB.