Strength characteristics of transversely isotropic rock materials

For rock materials, a transversely isotropic failure criterion established through the extended Lade-Duncan failure criterion incorporating an anisotropic state scalar parameter, which is a joint invariant of deviatoric microstructure fabric tensor and normalized deviatoric stress tensor, is verified with the results of triaxial compressive data on Tournemire shale. For torsional shear mode with 0 <= b <= 0.75, rock shear strengths decrease with a increasing until the rock shear strength approaches minimum value at alpha approximate to 40 degrees, and after this point, the rock shear strengths increase as alpha increases further. For the torsional shear mode with b > 0.75, rock shear strengths are almost constant for alpha <= 40 degrees, but it increases with increase in alpha afterwards. The rock shear strength variation against alpha agrees with shear strength changing tendency of heavily OCR natural London Clays tested before. Prediction results show that the transversely isotropic failure criterion proposed in the paper is reasonable.