To provide a method of cutting off water around a drift by composite grout, which is for use in geological disposal of high-level radioactive waste etc., and achieves water cutoff with high reliability by using a low-pH cement that is low in curing rate but is proof against alteration of a cushioning material and peripheral rock masses.

According to the method, a working face and the periphery and vicinity of the drift are frozen by a freezing method, and spring in the periphery and vicinity of the drift is temporarily stopped by a frozen region 2. After completion of water cutoff by the freezing method, the low-pH cement is injected into a region outside the periphery of the frozen region 2, and then cured, to thereby form an annular low-pH cement grout external region 3 enclosing the frozen region 2. Further, after melting of the frozen region 2, the low-pH cement is injected also into a working face peripheral area 2b on the periphery of the drift of the frozen region 2, and then hardened, to thereby form an annular low-pH cement grout internal region 4 enclosing the drift 1.