卸荷速率和孔隙水压力对砂岩卸荷特性影响研究

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。

Effect of unloading rate and pore water pressure on mechanical properties of sandstone

In order to study the effect of discharge load rate and pore water pressure on the mechanical properties of sandstone, the triaxial unloading tests with different unloading rates (0.005, 0.02, 0.05 and 0.1 MPa/s) and different osmotic pressures (0, 0.3, 0.6, 0.9 and 1.2 MPa) are designed and perfomed. The results show that: (1) At the loading stage, with the increase of the pore water pressure, the gradient of stress-strain curve of rock decreaseds gradually; (2) At the stage of unloading, with the increase of the unloading rate, the soft number of confining pressure is smaller, the confining pressure of rock failure is smaller, the rock strength is relatively high, but the degree of fragmentation is more serious. Moreover, under the same unloading rate, the higher the pore water pressure is, the more obvious the rock lateral expansion phenomenon is, and the rock is much easier to fail; (3) At the stage of unloading, the deformation modulus of rock shows a slow and steep trend, and the smaller the unloading rate is, the higher the pore water pressure is, the larger the deformation modulus deterioration amplitude is; (4) During the process of unloading, with the increase of the unloading rate, the features of rock brittle failure are more obvious. With the increase of pore water pressure, the number of axial tensile cracks and tracking secondary cracks near failure is larger. The stress concentration caused by the pore water pressure in specimen cracks or crack tips is the main reason that leads to the deformation failure. The related research results can provide good references for the analysis of the discharging mechanical properties of the hydrous rock mass.