中文摘要：

为了研究低孔隙水压力对砂岩卸荷力学特性的影响,在TOP INDUSTRIE多功能岩石三轴测试系统上,设计进行不同围压（5,10,15,20 MPa）和不同孔隙水压力（0,0.3,0.6,0.9,1.2 MPa）下的砂岩三轴卸荷试验。重点分析孔隙水压力对砂岩卸荷强度及变形破坏特征的影响。研究结果表明：（1）随着孔隙水压力的增大,岩样加载阶段的弹性模量逐渐减小,而且围压越小,相同的孔隙水压力增量条件下,弹性模量减小趋势越明显;（2）在卸载过程中,岩样侧向变形的增大速率明显大于轴向变形,而且,孔隙水压力越大,围压越小,侧向扩容现象越明显,岩样越容易破坏;（3）在卸载过程中,岩样的变形模量呈现先缓后陡的劣化规律,而且围压越小、孔隙水压力越大,变形模量降低幅度越大;（4）随着孔隙水压力的增大,岩样破坏时对应的围压值逐渐增大,黏聚力和内摩擦角降低趋势明显,说明孔隙水压力加速了岩石破坏的进程;（5）水对砂岩矿物颗粒的软化和颗粒间连接的弱化作用,以及孔隙水压力的水楔效应,是导致砂岩卸荷力学特性劣化的根本原因。因此,在涉水工程岩体卸荷变形稳定分析中,孔隙水压力的作用效应不容忽视。

英文摘要：

To study the effect on unloading mechanical properties of sandstone by low pore water pressure, triaxial unloading tests of sandstone under different confining pressure（5, 10, 15, 20 MPa） and pore water pressure （0, 0.3, 0.6, 0.9, 1.2 MPa） have been done in TOP INDUSTRIE Multi-function triaxial testing system. It has mainly been discussed about how pore water pressure influenced the sandstone＇s unloading strength and deformation and failure characteristics. The results showed that： （1） With the pore water pressure increasing, the elastic modulus in loading stage gradually decreased. And the decreasing trend of elastic modulus was more obvious under the smaller confining pressure with the same increment of the pore water. （2） During the unloading process, the increasing rate of lateral deformation was obviously higher than that of axial deformation. Moreover, the lateral expansion phenomenon is more obvious under higher pore water pressure and smaller confining pressure, which means the rock specimens are easier to damage. （3） During the unloading process, the deformation modulus of rock specimens decreased rapidly in the beginning and then slowly, and the rock specimens＇ deformation modulus declined dramatically with higher pore water pressure and smaller confining pressure. （4） With the increase of pore water pressure, the confining pressures related to rock specimens failure gradually increased, and the decreasing trend of cohesion and internal friction angle tend to be more obvious, which means the rock pore water pressure accelerates the process of rock failure. （5） The softening and weakening effect of water on the mineral particles and their inter-particle connection, and the water-wedge effect of pore water pressure are the basic reasons for sandstone＇s unloading mechanical properties deterioration. Therefore, concerning to the analysis of unloading deformation stability of wading rock engineering project, the effect of pore water pressure cannot be ignored.