STRENGTH AND DEFORMATION OF THREE TYPES OF RED BEDS UNDER CONVENTIONAL TRIAXIAL COMPRESSION

Complete stress-strain curves for sandstone,siltstone and mudstone in a red bed slope from east Sichuan province are obtained were obtained under confining pressures from 0 to 3 MPa using MTS815 Teststar,a rock mechanics servo system.The results showed that peak strength,yield strength and relaxation modulus vary with the confining pressure.The complete stress-strain curves can be divided into five phases: compacting,elastic,yield,strain softening and plastic flow.Elasticity modulus of the red bed increases rapidly with the confining pressure.Brittle failure is observed in sandstone and siltstone,while plastic failure is observed in mudstone.