辽西花岗岩水–岩耦合力学特性试验研究

EXPERIMENTAL RESEARCH ON MECHANICAL PROPERTIES OF GRANITE UNDER WATER-ROCK COUPLING

为了研究水–岩耦合作用对辽西花岗岩力学性质的影响,采用MTS–815岩石力学试验系统,通过对花岗岩试样施加不同的围压和孔隙水压力,对其变形破坏过程进行试验研究,分析水–岩耦合作用下辽西花岗岩的有效峰值强度、扩容现象、残余强度、峰后强度及其参数的演化规律。研究结果表明,有效峰值强度折减系数随孔隙水压力增大近似呈线性增长,但变化斜率随着围压增大而逐渐减小。在围压较小时孔隙水压对有效强度折减系数有明显的影响,在围压较大而孔隙水压较小时,施加应力压缩孔隙喉道抑制了孔隙水压对试样的作用。扩容起点是致密岩体水岩耦合作用增强的特征点,围压使得试样的扩容起点发生滞后,而孔隙水压力使得扩容起点提前发生,扩容现象与水岩耦合作用相互促进。水–岩耦合作用下试样的残余强度为对应状态峰值强度的21%~35%,Hoek-Brown常数随着围压的增大呈非线性增长,其值为3.5~5.0。峰后段试样的似内摩擦角变化不大,似黏聚力随着应变软化参数的增加有逐渐减小的趋势,而相同应变软化参数对应的似黏聚力则随着孔隙水压力的增大而减小,且似黏聚力、孔隙水压和应变软化参数间的关系可用3次样条曲面进行描述。

In order to study the influence of water on the mechanical properties of granite from Western Liaoning, the deformation and fracture of the granite were investigated with the mechanical test system of rock MTS–815. The effective peak intensity,volumetric dilation,residual strength,post-peak intensity and parameters of the granite were analyzed under different confining pressures and pore water pressures. The reduction factor of the effective peak strength was found to increase linearly with the increasing of pore water pressure and the slope of the linear relationship was reduced gradually with the increasing of confining pressure. When the confining pressure was smaller,the influence of the pore water pressure to the reduction factor of the effective peak strength was clearly notable. When the confining pressure was larger and the pore water pressure was smaller,the effect of pore water pressure was suppressed because the pore throat was compressed under the condition of applied stress. The starting point of volume expansion was found to be the characteristic point of enhanced water effect in dense rock. The confining pressure delayed the occurrence of expansion,while the pore water pressure promoted the occurrence of expansion. The volumetric dilation and water effect promoted each other. The residual strength under water effect is about 21% to 35% of the peak strength without water effect. Hoek-Brown constant increased nonlinearly with the increasing of confining pressure,and its value was between 3.5 and 5.0. At the post-peak stage of stress-stain curve,the change of pseudo internal friction angle was found to be small. The pseudo cohesion decreased with the increasing of strain softening coefficient,and it decreased with the increasing of pore water pressure when the strain softening coefficient was the same. The cubic spline surface was used to describe the relationship among the generalized cohesion,pore water pressure and strain softening parameter.