A clay grouting technique for granitic rock adjacent to clay bulkhead

Excavation and re-distribution of the stress around the tunnel lead to the development of an excavation damage zone (EDZ). While the bulkheads are keyed into the rock wall of the tunnel to act as cut-offs for the EDZ of the tunnel, clay grouting was conducted around the clay bulkhead as an additional measure to interrupt the connectivity of EDZ at the bulkhead. Clay grouting is being tested to determine if it is an effective method to reduce the permeability of fractured rock. The grouting into the EDZ is difficult because many of the fractures in the EDZ are connected with the excavation surface and cannot be filled efficiently by pressurizing the grout slurry. Therefore, the in situ injection tests of the clay grouting technique for the EDZ adjacent to the clay bulkhead were conducted to demonstrate the clay grouting technique and to estimate the ability of clay grouting to reduce permeability in the EDZ. This paper presents the results of these tests. Three in situ tests of clay grouting were performed during the Tunnel Sealing Experiment (TSX), conducted at Canada’s Underground Research Laboratory (URL) in the granitic rock to demonstrate technologies for tunnel sealing at full-scale. First, a clay grouting trial was conducted at a trial key in the tunnel about 25 m above the TSX tunnel. Secondly, the two series of clay grouting were performed in the TSX tunnel, on the upstream face of the key prior to the installation of the seal material of the clay key and later on the downstream side of the bulkhead. The results of these tests indicated a reduction in the permeability of granitic rock around the holes after grouting.