Assessment of the state of rock mass hosting large-span underground structures in the process of their long-term operation

The paper deals with the methods of assessment of rock state stress and the results of the in-situ study of underground hydrotechnical tunnels of the Verkhne-Teriberskaya and Borisoglebskaya HPS, the Kola Peninsula. Physical and mechanical properties of host rocks have been studied on samples and in-situ. It has been established that nature of excavation disturbed zone formed in the tunnel of rock mass contour is to a greater extent determined by mine working development technology and does not exceed values observed by mining practice. The number of fall-outs is small and conditioned by natural rock weathering along fractures in the course of continuous exploitation of mining workings. There have been revealed some tunnels sites, where regular monitoring of rock mass contour state is recommended.