Equivalent deformation modulus and strength parameters of surrounding rock for the underground powerhouse of three gorges project based on the modified GSI system

The influence of orientation of structure plane on parameters of rock mass is neglected in the study on the strength and deformation modulus based on geological strength index (GSI) system and Hoek-Brown strength rule. In this paper, as a case of underground powerhouse in the Three Gorges Project, the influence coefficient between the distribution of structure plane and structure rating (SR) of surrounding rock is calculated based on the space distribution character of excavated surface and structure plane; the statistical method of SR in the GSI system applied for large underground caverns is modified; and the experiential estimates of equivalent deformation modulus and strength parameters of surrounding rock are acquired. The investigations show that the calculative errors of the equivalent elastic modulus in elastic zone, deformation modulus and cohesive strength in disturbed zone of surrounding rock based on modified GSI system decreased by about 15%, 8%, 28% respectively.