Clay-Based Grouting Into the EDZ for the Vault Sealing

Abstract

In the Japanese concept for the disposal of the high-level radioactive wastes (HLW), the potential pathways for radioactive contaminant transport would be sealed by a combination of tunnel plug, backfilling and grouting. The candidate material for these engineered barriers would be bentonite or a bentonite-based mixture taking into consideration long-term stability of the seals. Two tests of bentonite grouting for sealing an excavation damage zone (EDZ), that exists in the rock in the immediate vicinity of the tunnel, were conducted in the granitic rock at Atomic Energy of Canada Limited’s (AECL’s) Underground Research Laboratory (URL). One test was the trial for the development of grouting procedure and the evaluation of grouting effectiveness, and the second test was a demonstration of the grouting around the clay-block bulkhead of the Tunnel Sealing Experiment (TSX). In the trial, the injection proportion of 4.0% of grout slurry was the most efficient. The result of the seepage test showed that grouting resulted in a reduction of hydraulic conductivity of the EDZ in the floor of the tunnel. In the demonstration, although the hydraulic pulse test didn’t indicate that the grouting significantly reduced the rock hydraulic conductivity, the test was a useful site-scale demonstration of bentonite grout injection for the purpose of EDZ sealing around a tunnel bulkhead.