Mechanical characteristics of intermittent jointed sandstone under triaxial compression

The mechanical properties of intermittent jointed rock mass directly affect the safety of engineering rock mass. In order to study its anisotropic mechanical properties and failure characteristics, the triaxial compression tests on the intermittent jointed sandstones with 6 joint inclination angles, 0°, 30°, 45°, 60°, 75° and 90°, are performed, and the effects of joint dip angle on the characteristics of deformation strength and failure modes of rock mass are analyzed. The results indicate that: (1) With the increase of confining pressure, the yield phase of stress-strain curve of intermittent jointed sandstone gradually becomes obvious, the peak and residual strengths gradually increase, and the characteristics of ductility are gradually obvious during destruction. (2) With the increase of joint dip, the deformation modulus, compressive strength, cohesion and internal friction angle of rock samples all present U-pattern change. (3) The joints have obvious induction and control effects on the formation and development of rock failure cracks. The fracture surfaces of the rock samples with different joint dip angles develop along the joint dip angle. When the joint dip angle is close to the calculated fracture one of the rock sample, the fracture surface of the rock sample is developed along the joint surface, and the deformation and strength parameters reach the minimum values. (4) With the increase of confining pressure, the difference of deformation and strength parameters of joints with different dip angles gradually decreases, and the anisotropy gradually weakens. (5) The failure modes of the intermittent jointed sandstone can be divided into three types: tensile failure, compound shear failure of fold line, and shear failure of joint surface, and the distribution of joint dip determines the deformation failure mode of sandstone under intermittent loading. The difference in deformation and failure modes determines the anisotropic characteristics of deformation and strength.