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).