Failure characteristics and the energy criterion of rock with a through-going joint under true-triaxial unloading conditions: Insights from the DEM model

Excavation unloading damages rock masses, with preferential failure along geological defects in rock engineering, which may induce catastrophe geological hazards. It is important to study the failure of jointed rock under true-triaxial unloading conditions. 3D DEM true-triaxial unloading modeling tests on rock with through-going joint considering the contributing factors, that is, the joint inclination, the initial confining pressure, and the unloading point, were conducted to study the rock mechanical properties, cracking behaviors, and failure characteristics. Six typical rock failure modes were summarized based on the development of main cracks, and the associated cracking mechanisms were studied by analysis of the ratio of tensile crack to shear crack. An energy criterion determining whether unloading-induced rock failure occurs instantaneously was proposed by comparing the accumulated elastic strain energy at the unloading point in true-triaxial unloading simulations with the limit elastic strain energy stored in rocks in biaxial compression modeling tests. Furthermore, the strength characteristics and applicability of the Mogi-Coulomb failure criterion in describing the failure of specimens with through-going joint under true-triaxial unloading conditions were studied. This study provides some new insights into true-triaxial unloading-induced failure of jointed rock, which may be valuable for revealing the mechanism of rock instabilities influenced by geological defects in deep excavations.