Experimental and numerical study on the shear behaviour of standard JRC double-joint rock masses

The shear resistance of multi-joint rock masses significantly affects the stability of underground engineering structures. In this work, using 3D printing technology, rock-like samples containing two joints with varying joint spacings and roughness values are prepared and subjected to direct shear tests under different normal stress conditions. The results demonstrate that the shear stress-shear displacement curve is influenced by the joint roughness coefficient (JRC) and normal stress. Peak shear stress increases with increasing JRC and normal stress but decreases with increasing joint spacing. Increases in JRC and normal stress increase the shear stress softening. The primary failure mode of the double-joint samples involves rock interlayer fracturing, the joint spacing has a smaller impact on shear failure mode than the JRC and normal stress. The shear failure behaviour and microcracking mechanism of a double-joint sample are revealed based on the developed cohesive zone model (CZM) method. Numerical tests revealed that the number of cracks in the double-joint model increases with increasing JRC and normal stress but decreases with increasing joint spacing. The model results in significantly more tensile cracks than shear cracks, tensile cracks are predominantly located in the rock interlayer of the double-joint model, whereas shear cracks are concentrated near the joint surfaces. This study explores the shear mechanical characteristics and microdamage behaviour of double-joint rock masses and offers foundational insights into the shear failure mechanisms of complex multi-joint rock masses.