To investigate the failure process and characteristics of D-shaped tunnels under different maximum principal stress directions θ, true-triaxial tests were conducted on cubic sandstone samples with a through D-shaped hole. The test results show that the failure process can be divided into 4 periods: calm, buckling deformation, gradual buckling and exfoliation of rock fragment, and formation of a V-shaped notch. With an increase in θ from 0° to 90°, the size of the rock fragments first decreases and then increases, whereas the fractal dimension of the rock fragments first increases and then decreases. Meanwhile, the failure position at the left side shifts from the sidewall to the corner and finally to the floor, whereas the failure position at the right side moves from the sidewall to the spandrel and finally to the roof, which is consistent with the failure position in underground engineering. In addition, the initial vertical failure stress first decreases and then increases. By comparing the results, the failure severities at different maximum principal stress directions can be ranked from high to low in the following order: 90°>60°>30°>45°>0°.

为研究D形隧道在不同最大主应力方向θ下的破坏过程和特征，对具有D形通孔的立方砂岩样品进行了真三轴试验。试验结果表明，破坏过程可分为4个阶段：平静、屈曲变形、岩屑逐渐屈曲剥落、V型缺口形成。随着θ的增加从0°到90°，岩屑尺寸先减小后增大，而岩屑的分形维数则先增大后减小。同时，左侧的破坏位置从边墙到墙角，最后到地板，而右侧的破坏位置从边墙到拱肩，最后到屋顶，这与破坏位置一致。在地下工程中。此外，初始垂直破坏应力先减小后增大。通过比较结果，不同最大主应力方向的破坏严重程度可以按照从高到低的顺序排列：90°>60°>30°>45°>0°。