Failure modes of weak interlayers with different dip angles in red mudstone strata, Northwest China

The shear mechanical behavior of weak interlayer is of great significance for the stability analysis of landslides. Based on the shear deformation-failure characteristics of weak interlayer soil and the clay damage theory, a shear failure mode is proposed to describe this kind of phenomenon. Triaxial compression tests and numerical simulation are conducted on weak-interlayer samples at conditions of different confining pressures and inclination angles. The numerical and experimental results show basically good agreement for both the peak strength and failure patterns. With increases in the thickness and dip angle (in the range of 0°–60°) of the weak interlayer, the shear strength of the samples decreased gradually. The weak-interlayer samples having a low dip angle were crushed and inflated; when the dip angle exceeded 15°, there was shear slip along the weak interlayer; when the weak interlayer was thin, the sample sheared along the structural plane; when the weak interlayer was thick, there was extrusion inside the weak interlayer or shear slip along the contact surface of the weak interlayer and mudstone. These results can improve our understanding of the mechanical behavior of mudstone rock mass with weak interlayers and can be used to analyze the stability of rock slopes or other rock engineering cases such as tunneling construction in rock mass with weak interlayers.