Abstract: To accurately determine mechanical parameters of the rock mass, an improved method for the quantification and correction of GSI value was proposed on the basis of the comprehensive analysis on some quantification methods of GSI value. Firstly, by using the scan line method, this study obtained the average spacing of joints (d) and rock mass block rating (RBR) which was a new quantitative factor based on rock mass block index (RBI). The volumetric joint count of rock mass (Jv) and rock mass structure rating (SR) were acquired according to the three-dimensional (3D) joint networks of the rock mass. Then GSI values of rock mass were quantified by utilising these above parameters, surface condition rating (SCR) and the joint condition factor (Jc). To overcome the drawbacks of GSI system, the correction method and formula of GSI value were established by considering the effects of joint orientation and groundwater on the mechanical parameters of rock mass. The established method was applied in a lead-zinc mine as an example. According to the new quantification and correction method of GSI value and Hoek-Brown strength criterion, the mechanical parameters of the ore body, hanging wall rock and footwall rock were determined. The accuracy and the feasibility of this method were verified by the comparative analysis with in-situ deformation tests. This study provides the theoretical and practical basis to acquire mechanical parameters of jointed rock mass based on rock mechanical tests in the laboratory.

Key words: rock mass mechanical parameters, quantification of geological strength index (GSI), correction method, Hoek-Brown strength criterion