In Situ Shear Test and Numerical Simulation of the Paleoweathered Jointed Rock Mass in the K1/J2 Contact Zone of the Ordos Basin

The crisscrossed joints produced by weathering will seriously affect the mechanical parameters of a rock mass, resulting in the frequent occurrence of engineering geological disasters. Taking the paleoweathered jointed rock mass (PWJRM) in K₁/J₂ contact zone of the Ordos Basin as the research object, the shear parameters of the PWJRM were tested using large-scale in situ shear test, namely the cohesion (C) is distributed between 44.2 and 96.9 kPa, and the friction angle (φ) is distributed between 19.8° and 66.32°. A numerical model considering joint thickness, joint roughness coefficient (JRC) and joint strength was established with MatDEM software. Numerical simulations under different vertical stress conditions reveal the shear mechanical properties and progressive failure mechanism of the PWJRM from a meso-level perspective. It is concluded that the peak shear strength is positively correlated with the joint strength and JRC, as well as negatively correlated with the joint thickness. Under the premise that the joint thickness is greater than the thickness of the joint surface roughness, the cohesion is positively correlated with the joint strength, JRC, and joint thickness. The friction angle is negatively correlated with the joint thickness but has little correlation with the joint strength and JRC. As the joint strength increases, the shearing process is controlled by tension cracks, and with increasing joint thickness, the shearing process is controlled by tension cracks and gradually becomes controlled by shearing cracks.