Strength Degradation of Fractured Sandstone After Thawing of an Inclined Shaft Produced by Artificial Freezing

Similar materials were used to make quasi-sandstone with parallel double fractures, and the process of freezing inclined shaft construction was reproduced through indoor freeze–thaw tests. The basic physical parameters of double fractured quasi-sandstone before and after thawing were measured, and indoor triaxial compression tests of double fractured quasi-sandstone with different dip angles after thawing were carried out. The influence of fracture dip angle on the mechanical properties and failure characteristics of the quasi-sandstone was analyzed. The results show the following. The double fractured quasi-sandstone had strong water absorption, and there were different degrees of freeze–thaw damage. Under triaxial compression, with the increase of fracture dip angle, the peak strength of the quasi-sandstone first increased and then decreased, and it was the minimum when the fracture dip angle was 30°. The energy evolution law was similar for different crack dip angles. In the elastic stage, the growth rate of elastic energy was greater than that of dissipated energy, whereas in the plastic stage, the dissipated energy gradually increased and exceeded the elastic performance. When the crack dip angle was 90°, the increase in the growth rate of dissipated energy was most significant. In addition, there were three main failure modes of quasi-sandstone under triaxial loading: when the dip angle of the fracture was 0°, wing crack propagation occurred in the rock, causing rock bridge failure. When the fracture dip angle was 30° or 60°, the rock was sheared. When the fracture dip angle was 90°, the rock was tensioned.