Analysis of the Failure Characteristics and Main Controlling Factors of Surrounding Rocks Using the Standard Specimen with a Pre-Existing Hole

To analyze the relationship between the butterfly-shaped plastic zone and stress in the rock with a single hole, we investigated the influence law of four factors, namely, the shape of the hole, the loaded confining pressure value, the bidirectional stress ratio, and the hole location on the volume of the butterfly-shaped plastic zone of the standard specimen with a single hole based on the orthogonal test and numerical simulation. The results show that: (I) The bidirectional stress ratio has a significant effect on the size of the plastic zone of the rock with a single hole, while the shape of the hole has no effect. (II) The basic value of confining pressure can weaken the sensitivity of the bidirectional stress ratio required to generate the butterfly-shaped plastic zone, that is, when the confining pressure value increases, the bidirectional stress ratio required to generate the butterfly-shaped plastic zone decreases, but there is always a certain value for the infinite expansion of the plastic zone. (III) The plastic zone of the rock with a single hole has a butterfly-shaped invariance, which means that the failure form of the surrounding rock around the hole will eventually evolve into a butterfly-shaped plastic zone under the state of a non-uniform stress field that reaches a certain bidirectional stress ratio. The research results of this paper have guiding significance for the stability control of the surrounding rock in underground engineering under the non-uniform stress field environment.