Evaluation of a compacted bentonite/sand seal for underground waste repository isolation

This study investigates the performance of an optimum compacted bentonite/sand mixture seal for the isolation of underground waste repositories. Engineering geological tests such as compaction, flow, swelling, mechanical and shear strength tests have been conducted to select an optimum mixture and to recommend a stable bentonite/sand seal length-to-radius ratio (L/a) as far as the factor of safety (F) is concerned. The results of the compaction permeameter tests led to a recommendation to select an optimum compacted bentonite/sand mixture possessing a bentonite content of about 20% to satisfy the minimum regulatory hydraulic conductivity requirement. Engineering geological analysis of the seal/rock mechanical interaction with regard to reduce the possibility of seal slip led to a recommendation to utilize a seal L/a of at least 25.