Adjustment of rock mass strength parameters using direct shear tests carried out on large blocks

摘要

Due to the complex nature of rock masses, geomechanical classifications are often used tornestimate indirectly strength parameters, such as the Geological Strength Index(GSI), developed by Hoek. Thisrnwork intends to compare the rock mass strength parameters assessed by the GSI index with those obtained inrndirect shear tests carried out on large blocks. The rock mass in study is characterized by the dominant presencernof carbonaceous phyllite, by the intense folding and weathering, by its ductile behavior and by presenting arndominant failure mode controlled by the rock mass properties. The tests were conducted in a servo controlledrndirect shear equipment on four undisturbed samples of 30×30×30 cm~3. It was found that the rock mass strengthrnparameters assessed by the GSI index were significantly conservative compared to the results of the shear tests.rnBased on these results, the input parameters of the generalized Hoek & Brown failure criterion were calibratedrnusing the RocLab software.