脆性岩石单轴循环加卸载试验及断裂损伤力学特性研究

 以向家坝砂岩单轴循环加卸载室内力学试验结果为基础，结合岩石内部微裂纹的细观力学分析，对脆性岩石单轴循环加卸载的应力–应变曲线特征、峰值强度及断裂损伤力学特性等进行研究。给出一种根据应力–应变曲线计算损伤变量的方法，损伤变量计算结果和声发射测试数据变化规律较为一致。试验结果表明，砂岩的循环加卸载强度要比单轴压缩强度要小很多，对于脆性岩石单轴循环加卸载的峰值强度来说，受到多种因素的影响。弹性常数计算结果表明，循环加卸载过程中泊松比逐渐增大，而弹性模量在第一次循环加卸载增大之后则缓慢减小。脆性岩石循环加卸载过程中，岩石损伤在逐渐累积，在微裂纹进入不稳定扩展阶段，岩石损伤会迅速增大，岩石宏观力学特性取决于内部微裂纹的细观力学响应。

EXPERIMENTAL TEST AND FRACTURE DAMAGE MECHANICAL CHARACTERISTICS OF BRITTLE ROCK UNDER UNIAXIAL CYCLIC LOADING AND UNLOADING CONDITIONS

Based on the uniaxial cyclic loading and unloading test results of the Xiangjiaba sandstone，combined with the mesomechanical analysis of the internal microcracks in rock，the characteristics of stress-strain curves，peak strength，fracture damage mechanical characteristics of brittle rock unloading condition are researched. A computational method for rock damage variable is presented based on the stress-strain curve；the acoustic emission test result shows that this method is reasonable. The experimental test results show that，the peak-strength of sandstone under cyclic loading and unloading conditions is less than that of the uniaxial compressive strength，which is influenced by lots of factors. Elastic constants of computation results show that，the Poisson's ratio is gradually increasing during the cyclic loading and unloading process，while the elastic modulus is increased evidently in the first cyclic loading and unloading process，and then decreases slowly. In the process of cyclic loading and unloading for brittle rock，rock damage will increase gradually，and rock damage will rapidly increase when the microcracks propagation runs into the unstable phase；the rock macromechanical characteristics depend on the mesomechanics response of microcracks.