非线性卸荷速率下的硬岩破坏特性与裂纹演化规律

为研究硬岩卸荷阶段速率非线性变化时的破坏特性，利用室内三轴压缩试验和颗粒流数值模拟开展余弦型、直线型和指数型三种卸荷速率变化方式的硬岩破坏研究.结果表明: 指数型卸荷的硬岩首先失稳破坏，余弦型卸荷的硬岩则不易发生破坏，前期较快的卸荷速率对整个卸荷过程的损伤积累影响更大； 硬岩卸载过程中的承载强度受初始围压和卸荷方式的共同影响，且围压愈高则卸荷方式影响愈显著； 根据Mogi-Coulomb准则，指数型卸荷通过内摩擦角影响硬岩强度，而直线型和余弦型卸荷的硬岩强度主要受黏聚力影响；指数型卸荷因前期快速卸荷易在端部产生部分破碎，直线型卸荷随围压升高由陡倾角剪切破裂带过渡多个“V”型剪切破坏，余弦型卸荷随围压增大呈塑性破坏特征趋势.

Failure Characteristics and Crack Evolution Laws of Hard Rock Under Nonlinear Unloading Rates

In order to study the failure characteristics of hard rock with nonlinear velocity variety in unloading phase， three unloading rate variety modes of cosine， linear and exponent were used to study the damage and failure of the hard rock by using the indoor triaxial compression tests and particle flow numerical simulation. The results show that the hard rock with exponential unloading rate first fails to stabilize， while the hard rock with cosine unloading rate is less likely to fail. The faster unloading rate in the early stage has a greater impact on the damage accumulation in the whole unloading process. The bearing strength of hard rock in unloading process is affected by both initial confining pressures and unloading modes， and the higher the confining pressure is， the more significant the influence of unloading mode is. According to the Mogi-Coulomb strength criterion， exponential unloading affects hard rock strength through internal friction angle， while the strength of hard rock under linear and cosine unloading mode is mainly affected by cohesion. Exponential unloading is easy to cause partial breakage at the end due to rapid unloading at the early stage. With the increase of confining pressure， linear unloading leads to multiple "V-shaped" shear failures from the steep dip shear fracture zone. Cosine unloading presents a plastic failure characteristic trend with the increase of confining pressure.