There are several voids in the ground behind lining concrete of aged tunnels. This induces the structural instability. It is necessary that these voids are filled with a backfilling grouting material to improve the stability of the tunnels. Conventional grouting materials have some problems, e.g. its high cost, and the difficulty in injection into targeted portions. We have developed a new grouting material to solve these problems. This grouting material consists of cement, bentonite, high water absorbent polymer, set accelerating agent and water. This paper reports on the design concept of this material, fundamental properties, the results of field experiments, and the applications to actual aged tunnels.
