基于单轴压缩的岩体破坏机制细观试验研究

Meso-experimental study of failure mechanism of rock based on uniaxial compression test

岩石在荷载作用下产生宏观破坏,其断裂面的细观形态变化,可以间接地反映岩石内部损伤演化进程,并与其宏观力学状态和结构破坏特性之间存在必然联系。主要对巴西劈裂试验和剪切试验试样的断裂面进行电镜扫描,总结典型力学特征下试样断裂面的细观形貌特征,建立裂纹断裂面细观形貌与宏观力学特性匹配的判断标准。进而对含不同倾角预制单裂纹试样单轴压缩试样的破坏全断面进行细观扫描分析,采用判断标准对其细观形貌判别,得到断裂面的拉剪应力分布权重,探究断裂面拉、剪应力分布随裂纹扩展过程的变化规律。试验结果表明:全断面拉剪应力权重与预制裂纹倾角有密切关系。预制裂纹倾角小于45°时,断裂面以拉应力为主,且随着裂纹扩展拉应力权重逐渐减小,剪应力权重逐渐增大;当裂纹倾角大于45°时,其结论与前述结论相反;预制裂纹倾角为45°时,拉、剪应力共同作用产生翼裂纹及次生裂纹2种扩展方式,翼裂纹扩展由拉应力主导向剪切应力主导过渡,次生裂纹扩展过程中主导应力变化规律与之相反。

The evolution of microscopic fabric of rock has an important effect on its mechanical property and failure shape and it is therefore essential to study the microscopic fabric on rock. In this study, the scanning electron microscope（SEM） was used to scan the micro structure of the failure section of samples after compression shear test and Brazil split test. The morphological characteristics of the fracture surface of specimen were highlighted and the criteria of microscopic morphology matching macroscopic mechanical properties of crack surface were established. Meanwhile, the whole failure section of manufactured pre-crack was scanned with different angles of inclination. The criteria was applied to distinguish their microscopic morphology. As a result, the ratio of tensile-shear stresses on the fracture surface was obtained. The variation of the ratio in the cracking propagation process was studied. The results show that the ratio of tensile-shear stresses is closely related to the dip angle of the pre-existing crack. When the inclination angle is less than 45°, the tensile stress on the fracture surface is high, and the ratio decreases with the crack angle increasing. When the inclination angle is more than 45°, the results are opposite to the former. When the inclination angle is 45°, there are two macroscopic cracks owing to the combined effect of tensile and shear stresses. The proportion of wing cracks tensile stress changes from high to low during crack propagation process, and the results of secondary crack are converse to the former.