Proposal of a practical guide of convergence measurements in Horonobe Underground Research Laboratory

Tsusaka, Kimikazu; Yamazaki, Masanao; Hatsuyama, Yoshihiro*; Yamamoto, Takuya*

The mechanical stability of a tunnel is subject to the development of loosening zone. In tunneling, convergence measurement is the most convenient method to estimate support requirements. In order to predict the final deformation and the development of loosening zone based on the measurement at the earlier stage of excavation work in 12 m span tunnels, one of the authors had proposed the Rock Behavior Classification in Tunneling (RBCT) had been proposed. Japan Atomic Energy Agency has excavated a 4.5 m diameter ventilation and a 6.5 m diameter access shafts in Horonobe, Japan. It is expected to build a practical guide to feed the results from the convergence measurement to the excavation work at deeper stages. Therefore, the authors evaluated the applicability of RBCT by means of analyzing the convergence curves in three tunnels with different dimensions and compared the convergence curves in the shafts with RBCT. As a result, it was clarified that the range of 0.07 to 0.3% in the final deformation ratio and the range of 13 to 15% wide loosening zone in the excavated diameter were estimated when the range of 0.02 to 0.1%/m in the initial deformation ratio was observed.