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为了研究卸荷速率和孔隙水压力对砂岩卸荷力学特性的影响,设计进行了不同卸荷速率(0.005,0.02,0.05,0.1 MPa/s)和不同孔隙水压力(0,0.3,0.6,0.9,1.2 MPa)下的三轴卸荷试验。研究结果表明:(1)在加载阶段,随着孔隙水压力的增大,岩样的应力–应变曲线斜率逐渐降低;(2)在围压卸载阶段,卸荷速率越大,卸载阶段的应变围压柔量越小,岩样破坏时的围压越小,岩样强度相对较高,但破碎程度更严重,而且,在相同的卸荷速率情况下,孔隙水压力越大,岩样侧向扩容现象越明显,岩样越容易破坏;(3)在围压卸载阶段,岩样的变形模量出现了先缓后陡的劣化趋势,而且,卸荷速率越小、孔隙水压力越大,变形模量劣化幅度越大;(4)卸载过程中,卸荷速率越大,岩样脆性破坏特征越明显;孔隙水压力越大,岩样破坏时的近轴向的张性裂纹越多和追踪次生裂纹越多,孔隙水压力在岩样内部裂纹、裂隙尖端的应力集中是导致岩石变形破坏的主要原因。
In order to study the effect of unloading rate and pore water pressure on unloading mechanical properties of sandstone, different unloading rates (0.005,0.02,0.05,0.1 MPa / s) and different pore water pressures (0,0.3,0.6,0.9 , 1.2 MPa) triaxial unloading test. The results show that: (1) The slope of stress-strain curve decreases gradually with the increase of pore water pressure at loading stage; (2) During unloading stage of confining pressure, the higher the unloading rate is, the strain at unloading stage The smaller the confining pressure and compliance, the smaller the confining pressure at the time of rock failure, the higher the strength of the rock specimen, but the more severe the fracturing. Moreover, under the same unloading rate, the larger the pore water pressure, (3) During the process of confining pressure unloading, the deformation modulus of rock samples shows the trend of first slow and then steepest, and the smaller the unloading rate, the larger the pore water pressure (4) During the unloading process, the greater the unloading rate, the more obvious the brittle failure characteristics of rock samples. The larger the pore water pressure, the more axial fractures near the rock specimen And tracking the more secondary cracks, pore water pressure cracks in the rock specimen, crack tip stress concentration is the main reason leading to rock deformation and destruction.