3.1 Failure modes of the specimens with holes and anchors
For failure modes of the rock with holes and anchors under the uniaxial compression test, refer to Table 2.
According to different bedding angles, the failure modes of the macroscopic cracks are primarily the shear failure (with a bedding angle of 0°) and the tension failure (with a bedding angle of 90°). The macro-cracks of the specimens with a bedding angle of 0° started from the collapse of the two side walls of the hole and developed along an oblique diagonal line to the opposite corner, and finally, they formed the single macro-failure surface on both sides (P1–3 and PC1–1). If the shear cracks on both sides of the hole wall develop along the upper and lower corners of the hole wall to form through-cracks, the specimen will eventually show the type X-I (M1–1) or X-II conjugate shear failure (BC1 –2). There are also specimens that only formed through-cracks on one side of the hole wall, and the cracks on the other side did not develop or developed from the hole wall only along the loading direction to one end of the specimen, which shows an inclined T-shaped type I (B1–3, BC1–2, and PCG1–2) or an inclined T-shaped type II shear failure (BCG1–3). Without considering the secondary cracks of the specimens, the simplified diagram of morphologies of the above three master cracks is shown in Figure 2(a). The macro-cracks of the specimens with a bedding angle of 90° are primarily controlled by the vertical bedding. The specimens underwent tensile splitting along with the bedding under the action of load, and the cracks on the controlled failure surface started from the collapse of the two side walls of the hole and then developed toward one end (BC2–3) or both ends (M2–1, B2–3, BCG2–2, P2–1, PC2–1, and PCG2–1) of the specimen along the vertical bedding direction. The simplified diagram of the master cracks is shown in Figure 2(b).
According to different crack formation mechanisms, it can be divided into three types: tensile crack (T_fracture), shear crack (S_fracture), and far-field crack (R_fracture). Tensile cracks can be divided into two types: one type is distributed in the tensile stress concentration area at the top and bottom of the hole, and the other type is distributed along with the vertical bedding, which is caused by the tensile stress of the bedding. The shear cracks start in the compressive stress concentration areas on both sides of the hole and gradually develop into the distance under the continuous load. Such types of cracks in the specimens with a bedding angle of 0° often develop into controlled failure cracks. The far-field cracks are the cracks located far away from the area around the hole. The above three types of cracks may not appear on the same specimen at the same time, but, through the crack type labels of the specimens in Table 2, it is not difficult to find that the specimens with mainly shear failure, such as the specimens with a bedding angle of 0°, must have shear cracks (S_fracture). Similarly, the specimens with mainly tensile failure, such as the specimens with a bedding angle of 90°, must have tensile cracks (T_fracture).