Evaluation of the loosened zone on excavation of the large underground rock cavern

When excavating large-scale underground caverns such as an underground pumped-storage power plant, in order to ensure the stability of the cavern and optimize the support system, the observational construction technique is used. Measurement data during construction are quickly processed and fed back to the construction at this site. In carrying out this technique accurately, it is important to evaluate precisely the conditions of the loosened zone around the cavern during excavation by monitoring, and to correctly predict the subsequent behavior of it by numerical analysis. This paper reports the measurement and analysis technology used at the Kan-nagawa power station and the observational construction technique.