Numerical analysis of the brittle–ductile transition of deeply buried marble using a discrete approach

In high geostress areas, rocks tend to experience plastic deformation processes and show ductility. Therefore, the study of the mechanical properties of rocks, especially the post-peak behavior, is crucial for underground geotechnical engineering. For this reason, the macroscopic mechanical property of marble is studied by using the PFC/PBM numerical method. An improved numerical marble sample with random properties is used by setting different contact strengths following a bimodal Weibull distribution. Thereafter, on the basis of an improved boundary servo mechanism, the brittle–ductile transition appearing in laboratory tests on marble is successfully realized by the discrete approach, and a servo velocity threshold function of axial loading speed and confining pressure is obtained. Furthermore, the marble model and servo method are applied in the excavation of typical underground caverns. The effects of constrained velocity and geostress level on the surrounding rock failure model of the cavern are described and analyzed. In addition, mechanism of the excavation failure under high geostress is discussed.