Estimation Method for Shear Strength Parameters of Fault Rock Based on Geological Strength Index

The existence of weak structural surfaces has a great influence for the stability of slope, and the shear strength parameters are the key values for slope stability evaluation. In this paper, the geological strength index (GSI) values are inversed base on the Hoek-Brown strength criteria and several triaxial compression test results of fault rock. Then, the shear strength parameters of fault rock mass can be determined by Mohr-Coulomb criteria and GSI values. The presented method is applied to estimate the shear strength parameters of black carbon schist in the F2 fault at the Jinping I Hydropower Station, where natural and saturated conditions are considered. Parameters estimation results show that the cohesion and the friction angle of the natural fault rock are 0.935 MPa and 40.15 degrees, respectively. Combined with uniaxial compressive strength of saturated rock mass and the corresponding softening coefficient, the cohesion and friction angle of the saturated fault rock are estimated as 0.759-0.812 MPa and 35.31 degrees-37.90 degrees, respectively; which are close to the suggestion values provided by the designer. The presented method can be used to estimate the reasonable shear strength parameters of fault rock mass based on GSI values even lack of geological information.