Effects of Intermediate Principal Stress on Compressive and Tensile Strengths of Sandstones

摘要

A series of polyaxial compression tests and indirect tension tests with axial confinements are performed to assess the effects of the intermediate principal stresses on the elasticity and strengths of three types of sandstones. Over 50 rectangular shaped specimens (50×50×100 mm) are tested using a polyaxial load frame. Lateral stresses with different magnitudes are applied on two mutually perpendicular directions (σ2 ≠ σ3), and varying from 0 up to 17 MPa. The axial stress (σ1) is increased until failure. The results are presented in form of octahedral shear strength (τoct) vs. mean stress (σm) diagram, indicating that under the same σm, σ2 can notably decrease the τoct at failure. The failure envelope is lower for the greater σ2/σ3 ratio. The results also indicate that the sandstones are transversely isotropic. The effect of intermediate principal stress (σ2) on the tensile strengths is assessed by conducting thTheeffectofintermediateprincipalstress(e Brazilian (indirect) tension test under axial conductingthconfinement. The σ2 value linearly decreases the failure loeBrazilian(indirect)tensiontestunderaxialad on the disk samples. A failure criterion (taken σ2 into consideration) can be developed using τoct - σm diagram and combining the tension test results with those of the true triaxial compression tests.