Abstract: The shear strength parameters of rock masses are generally most important and difficult to determine when performing stability analysis of rock works. Due to a large number of limitations existed in laboratory and in-situ experiments and uncertainties of empirical methods display, there has been a strong need to develop a new in-situ testing apparatus that can measure the shear strength parameters of rock masses in a quick and reliable way. Since a Rock Bore Shear Tester (RBST) made by Handy Geo. Instruments, Inc. was introduced by IWHR, a large number of laboratory and in-situ RBST experiments have been performed. The shearing mechanism, numerical simulation of RBST shearing process and its applications to Xiangjiaba dam site are presented. It can be found from the numerical analysis and in-situ testing results that RBST is applicable to soft and intermediate hard rock masses. The cohesion and friction angle determined by RBST are generally less than those determined by tri-axial and direct shear tests. In addition, the interal friction angle determined by RBST is a little less than that determined by triaxial and direct shear tests when <40?; and the cohesion c is considerably less than that determined by triaxial and direct shear tests by 25%-50%.

Key words: rock borehole shear test, shear strength, jointed rock mass, in-situ testing