Study on mechanical response and fracture characteristics of rock under full path unloading

Abstract

Abstract When the underground roadway of the coal mine passes through the abnormal area of geological structure (fault, collapse column, fracture zone, etc.), the excavation induces the unloading instability of engineering rock mass. The rock mass in the fracture zone is in elastic, plastic, and post-peak stress states. The process of excavation through the fracture zone is essentially unloading from the full stress path. To explore the mechanical response to sandstone under different stress levels, based on the study of the possibility of stress path, the elastic axial pressure unloading confining pressure, the elastic principal stress constant unloading confining pressure, the plastic axial pressure unloading confining pressure, the plastic principal stress constant unloading confining pressure, the plastic axial D1 displacement constant unloading confining pressure, the plastic axial pressure confining pressure proportional unloading, and the post-peak axial pressure confining pressure synchronous unloading path are systematically carried out. The characteristics of a full stress-strain curve under 7 unloading paths are obtained, the deformation law caused by unloading is analyzed, and the relationship between the unloading path and strain increment is studied. It is obtained that with the increase of unloading degree, the unloading deformation modulus E in the elastic stress state first increases, then stabilizes, and then decreases, and the unloading deformation modulus E in the plastic stress state gradually decreases, Poisson's ratio µ both showed an increasing trend, normalized plastic shear strain \({\gamma ^p}/\gamma _{{\hbox{max} }}^{p}\) and dilatancy angle ψ according to the single exponential function, the initial confining pressure is negatively correlated with the dilatancy angle, and the research results can support the enrichment and development of unloading rock mechanics.