Mechanical behaviour of rock samples containing multiple parallel joints during shearing

This study experimentally investigated the influence of number of joints on the mechanical behaviour of multi-joint samples during shearing under constant normal stiffness (CNS) boundary conditions. A series of samples that have different surface roughness and different numbers of joints are prepared, and the variations in shear stress, normal stress, normal displacement are analysed. The relationship between surface resistance index (SRI), defined as the ratio of shear stress to normal stress, and number of joints are estimated. The results show that with the increment of number of joints, the damage degree of the samples increases. For a multi-joint sample, the middle joint is most significantly damaged. When the shear displacement is small, the shear stress decreases with increasing the number of joints. However, when the shear displacement is large, the shear stress does not exhibit clear relationships with the number of joints. The SRI has clear peak values against shear displacement, and the peak SRI decreases linearly by increasing the number of joints, while the peak shear displacement increases following quadratic functions. Finally, two new regression functions are proposed to predict the variations in peak SRI and peak shear displacement for multi-joint samples during shearing under CNS boundary conditions.