ABSTRACT
Knowledge of the rock mass strength is required for the design of many engineering structures to be built in or on rocks. For this purpose, it is necessary to obtain design parameters such as deformation moduli, peak and residual strength parameters, and dilation angle for numerical modeling and design. The GSI system, proposed by Hoek et al. (1995), is now widely used for the estimation of the rock mass peak strength and the rock mass deformation parameters. A quantitative approach to assist in the use of the GSI system is presented. It employs the in-situ block volume and a joint condition factor as quantitative characterization factors to determine the peak GSI value. To use the GSI system to estimate the residual strength of jointed rock masses, the peak GSI can be adjusted to a residual GSIr value based on the two major controlling factors in the GSI system, i.e., the residual block volume and the residual joint surface condition factor. Methods to estimate peak and residual block volumes and joint surface condition factors are presented. In addition, a detailed discussion on the determination of other design analysis input parameters, such as uniaxial compressive strength of intact rocks and Hoek-Brown constant mi are given and a method to estimate dilation angles of rock masses is presented.The determined Hoek-Brow rock mass strength parameters, dilation angles, and deformation modulus can be used in numerical analyses for safe and cost-effective engineering design. Because of its quantitative nature, this approach allows the consideration of variability of rock mass strength and deformation parameters in design, using the Monte Carlo or point estimate method.
