2006 年 55 巻 5 号 p. 495-500
In Japan, it is planned to dispose a part of low-level radioactive wastes in stable geological formations. Taking the long-term behaviors of the formations into account, a mathematical model is of prime importance. As far as the long-term behaviors of materials, the Norton-Baily creep model is so common usage. However, the value of creep strain is not converged as time advances. This is because it is a power function for time. Therefore, authors modified the Norton-Baily creep model so as to remove its demerit and proposed a creep model for soft rock mass with considering both a time hardening and a strain hardening. The modification brought about numerical results close to real behaviors of the rock mass. In this study, the proposed model is employed to analyze the long-term behaviors of underground cavern surrounded by soft rock mass and to discuss the effect of shotcrete since the effect of shotcrete on the long-term behaviors of the rock mass has not been well discussed. It is turned that the installation of shotcrete affects not only short-term behaviors of the rock but also long-term ones. The important role that the shotcrete for underground cavern plays in long-term behaviors should be clarified in the consideration of radioactive waste disposal.