A Note on Partial Safety Factors for In-situ Shear Strength Parameters of Rock-Mass

The design of retaining structures founded on jointed rock-mass must ensure their safety against sliding instability. For this purpose, generally, in-situ direct shear tests are conducted and shear strength parameters (cohesion and friction-angle) are determined using the popular Mohr–Coulomb criterion. However, due to assumptions associated with such a simple shear strength criterion and various other uncertainties, random errors and limitations associated with in-situ testing, the shear strength parameters are also associated with uncertainties. The present study discusses a practise-friendly procedure to account for such uncertainties and investigates the efficacy of the current design practice (IS 6512) in accounting for these uncertainties. The proposed procedure is explained through four case-studies of in-situ direct shear tests conducted in Phyllite and Granitic rock-masses and evaluating sliding safety of a hypothetical concrete gravity dam founded on those rock-masses. The study highlights the fact that IS 6512 may lead to an unsafe design in cases when uncertainties associated with in-situ shear test data are significant.SCOPUS: cp.k