围压及孔隙水压对饱水砂岩能耗特征的影响

Confining Pressure and Pore Pressure Effect on the Energy Dissipation of Water-saturated Sandstone

为研究含孔隙水压下岩石承载变形过程中的能量演化特征,基于有效应力原理推导出含孔隙水压下岩石承载变形过程中的能量计算公式.分析了围压和孔隙水压对岩石承载变形过程中能耗特征的影响,讨论了岩石输入能密度、弹性能密度和耗散能密度在扩容起始点和峰值点的差异,从能量耗散的角度解释了岩石扩容起始应力作为岩石长期强度参数的合理性.研究表明:岩样在扩容起始点和峰值点的输入能密度和弹性能密度与围压呈正线性关系,与孔隙水压呈负线性关系.岩样承载过程中的cd-c阶段的耗散能密度随围压的增大而增大,而孔隙水压的增大则导致该阶段耗散能密度的减小,其有效地弱化了岩石材料内部颗粒间的摩擦效应.此外,孔隙水压能量输入密度随岩样的体积应变变化,在高孔隙水压条件下,相同应力水平的各类能量输入密度的绝对值随孔隙水压的增大而增大.

In order to study the energy evolution of rock under loading with pore pressure,acalculation formula of energy was derived by the effective stress principle.The effects ofconfining pressure and pore pressure on the energy dissipation of rock were analyzed inloading process.The differences among the densities of input,elastic and dissipatedenergy at the points of dilatancy onset and peak were discussed.From the perspective ofenergy dissipation,the rationality that the stress of dilatancy onset could be the long-term strength parameter of rock was explicated.The results show that the relationsbetween the densities of input and elastic energy and the confining pressure present thepositive linearities,but the relations between those and the pore pressure perform thenegative linearities.The density of dissipated energy increases with the confiningpressure in cd-c stage of loading process.However,the increase of pore pressure causesthe decrease of dissipated energy density in this stage,it effectively weakens thefrictional effect among the internal particles of rock material.In addition,the inputenergy density of pore pressure varies with the volumetric strain of the specimen.Theabsolute values of all types of input energy density increase with the pore pressure at thesame stress level under the condition of high pore pressure.