受载岩石能量演化的围压效应研究

CONFINING PRESSURE EFFECT ON ROCK ENERGY

能量演化贯穿于岩石变形破坏的全过程,为了探究围压对受载岩石能量演化特征的影响规律,对红砂岩试样进行6种固定围压下的轴向加、卸载试验,揭示岩石弹性能和耗散能演化及分配规律的围压效应,并探讨工程采动岩体的能量演化路径。研究结果如下:(1)提出岩石储能极限、最大耗散能密度、残余弹性能密度3种特征能量参数,可分别表征岩石的能量积聚、耗散和释放行为特征;(2)峰前主要表现为能量积聚,峰后主要表现为能量耗散和释放,但随着围压的增高,岩石储能极限大致呈幂指数增长,残余弹性能密度呈线性增加,最大耗散能密度呈幂指数增加,表明围压增大了能量输入的强度,减弱了能量释放的烈度;(3)围压越大,弹性能比例在峰前阶段越大,在峰值破坏时下降幅度越小,在峰后阶段二次上升所达到数值越接近于峰前值,表明围压提高了能量积聚的效率,提升了岩石破裂重组后的储能能力;(4)工程采动岩体失稳破坏的能量路径是增加储能水平和降低储能极限2条途径的组合,能量路径斜率越大,越容易因为围压的突然卸载而发生强能量释放行为。

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.