关键词: 硬脆性, 脆性破坏, 拉剪试验, 压剪试验, 屈服准则

Abstract: The yield criterion of materials in geotechnical engineering is generally presented on the basis of the compression-shear failure type. However, brittle hard rock has three types of failure, i.e., tensile failure, tension-shear failure and compression-shear failure. With increasing the depth of rock engineering, the tension-shear failure turns into the main failure mechanism of surrounding rock. Tension-shear tests are conducted on brittle hard marble to investigate the characteristics of tension-shear failure. By analyzing tension-shear and compression-shear testing results, a modified Mohr-Coulomb criterion is established, which can consider the effect of tension-shear failure and stress state. It is noted that the failure of brittle hard marble is in tension-shear at the tension-shear stress state and at the compression-shear stress state with a low normal axial stress, but it shows compression-shear slip characteristic at the compression-shear state with a high normal stress. The failure of marble is dominated by obvious tension cracks at tension-shear stress state, while no obvious shear crack appears. The shear displacement increases with the increase of axial tensile stress when the shear stress is fixed. The cohesion and friction angle are influenced by the stress state. The cohesion decreases initially and then increases with increasing the normal stress, while it is opposite in the friction angle. The variations of the cohesion and friction angle with the normal stress can be divided into four stages: tension-shear, low compression stress, medium compression stress and high compression stress. The relationships between cohesion, friction angle of each stage and normal stress are linear, and the friction angle reaches up to 90 degrees while the cohesion approaches infinitely to tensile strength. By considering the effect of tensile shear failure and stress state, the Mohr-Coulomb criterion curve can be divided into two stages, the tension-shear stage which is fitted with a second-degree parabola and the compression-shear stage considering the development of cohesion and friction angle with the normal stress. It is demonstrated that the proposed Mohr-Coulomb criterion is comprehensive and precise.

Key words: hard brittleness, brittle failure, tensile shear test, compression shear test, yield criterion