Experimental study on mechanical characteristics of unloaded damaged white sandstone before peak

In order to study the problem of deformation and failure caused by rock unloading during excavation and mining, a three-axis loading-unloading-uniaxial reloading mechanics with different confining pressures and different initial axial pressures was applied to white sandstone specimens with the RMT-150 testing machine characteristic test. The damage and weakening mechanisms of white sandstone specimens during triaxial loading, unloading, and uniaxial reloading were analyzed. The experimental results show that the peak strength of the specimen has a linear relationship with the confining pressure. The greater the confining pressure, the higher the peak strength of the white sandstone specimen. The peak strength of the specimen and the initial axial compression load ratio (the ratio of the initial axial compression to the triaxial peak load intensity) and the porosity have a 3rd-order polynomial relationship. The damage and weakening of the strength of the rock specimen are related to the load history. The greater the initial axial pressure, the faster the reloaded specimen from the crack closure to the elastic deformation under steady-state damage to the accelerated elastic-plastic deformation under accelerated damage, and the smaller the peak load strength after unloading the specimen. In addition, combined with the loading history of rock, a strength weakening calculation method based on the loading process state is proposed. After verification, this method is feasible.