Study of the effect on surrounding rock and groundwater from shotcrete using low alkaline cement in Horonobe URL

Nakayama, Masashi ; Okamoto, Reiko*; Shirase, Mitsuyasu*

In Japan, high-level radioactive waste repository will be constructed in a stable host rock formation more than 300m underground. Tunnel support is used for safety during the construction and operation, and shotcrete and concrete lining are used as the tunnel support. Low alkaline cement has been developed for the long term stability of the barrier systems whose performance could be negatively affected by highly alkaline conditions arising due to cement used in a repository. JAEA has developed a low alkaline cement, named as HFSC (Highly fly-ash contained silicafume cement), containing over 60wt% of silica-fume and coal ash. HFSC was used experimentally as the shotcrete material in construction of part of the 140m, 250m and 350m deep gallery in Horonobe URL. JAEA has been carrying out the investigation about interaction among cement, rock and groundwater using core samples of shotcrete and rock. In this report, the effect on surrounding rock and groundwater from shotcrete using HFSC is described through comparison with that from shotcrete using OPC.