Triaxial Experimental Study on Changes in the Mechanical Properties of Rocks Under Different Rates of Confining Pressures Unloading

To determine the relationship between the unloading rate and the rock's mechanical properties, an experimental study on specimens of granite at different unloading rates was conducted. The results of the study show that during unloading, the axial strain increases slowly and the lateral expansion of the rock sample is considerable. The slower the confining pressure unloading rate, the more thoroughly the fissures propagate through the rock and the more complete the stress transfer. The result is that more fracture surfaces are produced and the rock is broken more fully. Conversely, if the confining pressure is unloaded more quickly, the crack propagation and stress transfer are terminated abruptly and the rock specimen can only generate a few rupture surfaces along the initial rupture direction. Rock samples are easier to break when unloaded at a greater rate, and the stress difference at break is smaller. Poisson's ratio increases with decreasing confining pressure. The research results provide a theoretical basis for the prevention and control of geological disasters in deep rock excavations.