ABSTRACT

A polyaxial load frame has been used to determine the compressive strength of Phra Wihan sandstone under true triaxial stresses. The rock specimens are cubic shape with a nominal dimension of 5×5×5 cm3 . Under a low σ3, σ1 at failure initially increases with σ2 and then decreases with σ2. Under a high σ3, σ1 increases with σ2. The Coulomb and modified Wiebols & Cook failure criteria derived from the characterization test results predict the sandstone strengths in terms of J2 1/2 as a function of J1 under true triaxial stresses. The modified Wiebols & Cook criterion describes the failure stresses better than does the Coulomb criterion.