Rock Failure under Unloading Conditions and Application for Rock Burst

The behavior of rock deformation and its failure characteristics under loading and unloading conditions are substantially different. Rock burst during excavation of underground engineering in areas of high geostress is a typical failure phenomenon due to unloading. Triaxial unloading tests are designed to simulate the unloading process during underground excavation. Rock specimens are firstly compressed in a triaxial cell and then the confining pressure is reduced progressively while keeping the axial deformation constant. Experimental results show that specimen absorbs energy during axial compression loading and release energy during failure at confining reduction. Strain energy stored in rock is sufficiently large to cause failure when it is released. To prevent rock burst, one of the basic methods is to release the strain energy in rock before excavation. Pre-boring has been successfully used to release the strain energy and to prevent the outburst in mines. Rock burst could also be controlled or released by adjusting the speed of excavation.