Rock failure induced by dynamic unloading under 3D stress state

• A numerical method of initialization-dynamic unloading process is presented.
• The SED and SED rate dominated the unloading process of rock under 3D stress state.
• The equivalent SED rate was introduced to quantitatively describe the unloading process.

A commercial finite element program, LS-DYNA, was employed to simulate the unloading process of rocks under three dimensional (3D) stresses. The continuous surface cap model (CSCM), was used to model rock behaviour. Using this model, the unloading failure mechanisms of hard rock in a confined state were investigated during the unloading process. The results indicated that when rocks under 3D stress state experience unloading, the process is dominated by strain energy density (SED) rate. The effects of different unloading paths and different confining stresses can be characterised by the SED rate. A significant finding of this study is that the SED rate can quantify the unloading process. Based on the findings, rock failure can be induced by rapid unload of initial stress. In the practical underground excavation engineering, dynamically controlling the SED rate can increase the excavation potential of rocks, minimising the required external excavation energy by using the energy of the stressed rock.