Determination of c and phi of rocks from indirect tensile strength and uniaxial compression tests

Cohesion (c) and friction (phi) angle are the two key parameters required in numerical simulations and designs of underground openings, excavations, and foundations in rocks. The paper discusses a simple method, based on a theoretical framework, to determine the two parameters from uniaxial compression test and indirect tensile strength test. Laboratory tests were carried out on 35 rock specimens and the values of c and phi were computed. The predicted values of c appear to be more realistic than those of phi, and the scatter is attributed to the anisotropy and heterogeneity generally observed in the rock cores. The computed value of c is 1.82 times the indirect tensile strength (sigma(t)).