Development of a system to measure the in-situ mechanical conditions and to evaluate easiness of underground construction in the weak sedimentary rock

Ishijima, Yoji*; Fujii, Yoshiaki*; Kawakita, Minoru*; Nakama, Shigeo ; Matsui, Hiroya 

The ratio of soft rock occupied in the whole rock mass in Japan is relatively high. Strata control problems occur more frequently in soft rock than in hard rock, since fracture and large deformation are easily induced in soft rock whose strength and stiffness are small in magnitude. A rational method to overcome these problems is to develop such system to measure the rock stresses as well as to evaluate the in-situ strength of the rock mass and to use these data to predict the phenomena occurred during nderground constructions and to reflect them to design of the rock mass structure. However, the technique of measurements which can be used in soft rock has not been developed to this day, due to many problems to overcome. Purpose of the present investigation is to develop a system to measure such components as the rock stress, the width of the fissured one and the creep deformation, by using a single borehole drilled in the soft rock. To confirm the validity of this system, the in-situ measurements were conducted in the soft iatomaceous mudstone in Horonobe district, Hokkaido, Japan. Various findings obtained in this investigation will be reported.