致密砂岩循环加载试验及能量演化分析

为研究复杂应力路径下致密砂岩的力学行为，采用多功能岩石三轴测试系统开展围压为5 MPa、15 MPa和20 MPa的三轴循环加卸载试验并进行能量演化分析。试验结果表明:砂岩的抗压强度随着围压增加而增大，围压5 MPa、15 MPa、20 MPa下的体积最大压缩点对应的轴向偏应力分别为80.68 MPa、120.72 MPa、152.12 MPa；加卸载过程中会有部分外荷载做功转化成内能和其他形式能量，因而应力-应变曲线形成滞回环，并且随着应力的增加滞回效应逐渐明显；砂岩以剪切破坏形式为主，同时产生轴向和侧向倾斜裂纹。能量演化分析表明:岩石的破坏是弹性能积累到峰值突然释放的结果；岩样破坏前的峰值弹性能会随围压线性增加，围压对峰值弹性能的影响显著。

Cyclic loading test and energy evolution analysis of tight sandstone

In order to study the mechanical behavior of tight sandstone under complex stress paths, the multi-function rock triaxial test system was used to carry out three-axis cyclic loading and unloading tests with confining pressures of 5 MPa, 15 MPa and 20 MPa, and then, energy evolution analysis was carried out. According to the results of the tests, the compressive strength of sandstone increases with the increase of confining pressure. The axial deviatoric stresses at the maximum compression point with confining pressures of 5 MPa, 15 MPa, and 20 MPa are 80. 68 MPa, 120. 72 MPa, and 152. 12 MPa, respectively. During the loading and unloading process, some of the damage is converted into the internal energy and other forms of energy, so the unloading curve is lower than the loading curve and hysteresis loops appear. As the load increases, the hysteresis effect is getting gradually obvious. The failure of sandstone is dominated by shear failure and produces axial and lateral sloping cracks. Energy evolution analysis shows that the energy dissipation is the cause of damage to the rock mass. The peak elastic energy before the failure of rock sample increases linearly with the confining pressure, and the effect of confining pressure on peak elastic energy is significant as well.