The strength of rock under combined compression and shear loading has been paid more and more attention, but still lacks a theoretical model that incorporates both compression–shear characteristics and influence of dip angle to estimate the strength of the rock. This work is aiming to solve the issue by combining experimental and theoretical methods. First, in the laboratory, 112 rock samples with different sizes were applied to obtain the dip effect characteristics of strength via combined compression–shear tests. The ratio of compression–shear strength to uniaxial compression strength is called the compression–shear coefficient, which is used to characterize the degree of dip effect. Second, according to the compression–shear load characteristics of inclined rock samples, a strength model was established considering both compression–shear characteristics and dip angle by the Mohr–Coulomb failure theory. This strength model is an extension of the Mohr–Coulomb criterion and was verified by experimental data. The verification results are consistent with experimental results. Finally, the mechanism of dip effect on strength was explained from the resistance to the sliding and stress path of the rock sample. The results show that the dip effect is an inevitable strength weakening characteristic of rock materials under combined compression–shear loading. Compared with the vertical rock sample loaded under pure pressure, the resistance to the sliding of inclined rock samples decreases and the stress path is changed, which reduces the ability of the rock sample to resist external loads, resulting in the decrease of strength.

中文翻译：

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用实验和理论模型研究倾角对倾斜岩样单轴抗压强度的影响

岩石在压剪联合荷载作用下的强度越来越受到重视，但仍缺乏结合压剪特性和倾角影响来估计岩石强度的理论模型。这项工作旨在通过结合实验和理论方法来解决这个问题。首先，在实验室中，应用112块不同尺寸的岩石样品，通过压缩-剪切联合试验获得强度的倾角效应特征。压缩剪切强度与单轴压缩强度的比值称为压缩剪切系数，用于表征倾角效应的程度。其次，根据倾斜岩样的压剪荷载特性，通过Mohr-Coulomb破坏理论建立了同时考虑压缩-剪切特性和倾角的强度模型。该强度模型是 Mohr-Coulomb 准则的扩展，并通过实验数据进行了验证。验证结果与实验结果一致。最后，从岩样的抗滑性和应力路径解释了倾角对强度影响的机理。结果表明，倾角效应是岩石材料在压剪联合荷载作用下不可避免的强度减弱特性。与纯压力加载的垂直岩样相比，倾斜岩样的滑动阻力减小，应力路径改变，降低了岩样抵抗外载荷的能力，