(1. State Key Laboratory for Geomechanics and Deep Underground Engineering，China University of Mining and Technology，Xuzhou，Jiangsu 221116，China；2. School of Mechanics and Civil Engineering，China University of Mining and Technology，Xuzhou，Jiangsu 221116，China)
Abstract：Energy varies during the whole process of rock deformation and failure. In order to investigate the effect of confining pressure on rock energy variation，axial loading and unloading tests under six different confining pressures were conducted for sandstone samples. The confining pressure effects on variation and allocation pattern of elastic energy and dissipated energy were revealed，and the energy path of engineering rock mass was discussed. Three characteristic energy parameters，i.e. the energy accumulation limit，the maximum dissipated energy density and the residual elastic energy density，were proposed to describe the accumulation，dissipation and releasing of energy respectively. Rock energy variation under different confining pressures was found to be similar. The energy accumulation occurred mainly before the peak stress while the energy dissipation and releasing were dominant in the deformation stage after the peak stress. As the confining pressure increased，the maximum accumulated rock energy increased exponentially，the residual elastic energy density increased linearly，and the maximum dissipated energy density risen exponentially，indicating that the confining pressure enlarged the rock energy transmission and weakened the intensity of energy release. The greater the confining pressure was，the larger the elastic energy ratio in the stage before peak stress，the less the elastic energy ratio fall at the peak point，and the more closely the elastic energy ratio approached the maximum value when it rose again after the fall，indicating that the confining pressure enhanced the efficiency of energy accumulation，and elevated the energy storing capacity of fractured rock. The energy path of rock mass leading to buckling failure is a combination of the ones of enlarging the energy accumulation level and reducing the energy accumulation limit. When the slope of energy path is large，the rock mass stored a large quantity of energy reaches the critical state，and the sudden unloading of confining pressure can lead to energy releases strongly.
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2015, Vol. 34 
