ENERGY CHARACTERISTICS OF BRITTLE FAILURE OF GRANITE ROCK BRIDGE UNDER UNLOADING COMPRESSION

The failure of locking section of rock bridge is closely related to the cumulative and release of energy. The conventional triaxial loading test and triaxial loading and unloading test were carried out for granite rock bridge sample using the MTS815 servo control rigid mechanical testing machine. The variation trend of energy in various stages before the loading peak can be effectively compared and analyzed under different loading conditions using the energy analysis method on the basis of the axial stress ratio. The result shows that the variation of energy characteristics before stress peak is mainly divided into compaction stage and elastic stage. When the specimen is in the compaction stage, the energy dissipation ratio increases with the initial crack closure and friction. During the elastic stage, most of the work done by the load is converted to elastic energy and stored in the specimen, and the elastic energy ratio increases substantially. As the existence of prefabricated crack, the yield stage does not appear obviously before the destruction, and the "burst type" brittle failure of rock bridge sample is presented. The total energy and elastic energy at point of stress peak will have a significant increase with the increasing of initial confining pressure. With the growth of the rock bridge's length, the absorption of total energy and limit elastic energy storage are increased gradually, the ratio of elastic energy to total energy is also increased at the point of stress peak, while the length of the rock bridge has little influence on the dissipated energy.