The stress–time curves of phyllite and yellow sandstone are shown in Fig. 5. For the phyllite samples at various bedding angles, due to the varied bearing capacities of the phyllite, the vertical stresses are loaded to 64 MPa, 74 MPa, 30 MPa, 30 MPa, 48 MPa, 108 MPa, and 76 MPa, as shown in Fig. 5(a)-(g), respectively. For the yellow sandstone, when σz was increased to 30 MPa, no macroscopic failure was produced on the “D” shaped hole sidewall. Meanwhile, σz was increased by step loading
