Abstract

Most of hydropower tunnels have squeezing problems due to weak rock mass quality and high overburden. The induced stress level exceeds the strength of rock mass tunnel fails. Stress plays a crucial role in developing brittle fractures, rock strength reduction and rock mass instabilities the critical stress is an indicator for the support design of tunnel. To quantify stress state and deformation of circular tunnel, an empirical, semi analytical and a two-dimensional boundary element numerical analysis have been made in this paper. Initially, rock mass characterization is carried out by using Q and RMR methods which defined rock mass as poor to good and fair respectively.
Then for identification of squeezing empirical approaches are used, results shown that there is no squeezing in the tunnel. However, 200 m stretch of tunnel undergoes severe squeezing as identified by Hoek and Marinos approach which is further refined by using Numerical program phase2 which yields displacement values quiet nearer to values obtained by semi-analytical approach by considering rock mass as plastic material. Tunnel support is estimated by using Q and RMR systems respectively which is verified by Numerical analysis.

Keywords: Tunnel; Support system; Squeezing; Hoek and Marinosmethod