Study on transient unloading loosening simulation test of excavation of jointed rock mass

Based on the abrupt displacement of a jointed surrounding rock mass during blasting excavation of deep underground caverns, a set of transient unloading loosening simulation tests was designed for multi-joint rock masses. Through the linear regression analysis of the unloading displacement of jointed rock masses, the opening displacement of a joint is determined to be proportional to the square of the initial unloading stress. The numerical simulation method is used to apply horizontal and vertical in situ stresses to the jointed rock mass model to study the opening displacement in the jointed rock mass at different lateral pressure coefficients of in situ stress. The results indicate that, with the unloading of the horizontal stress, a larger lateral pressure coefficient of the in situ stress leads to a larger opening displacement in the jointed rock mass. When the vertical stress is unloaded after the horizontal stress is totally unloaded, a lower lateral pressure coefficient of the in situ stress leads to a larger opening displacement. The influence of the stress lateral pressure coefficient on the open deformation of the jointed rock mass is obviously higher than that of the unloading rate on the rock mass.