不同加载速率下砂岩弯曲破坏的细观机理

岩石细观破裂形貌是岩石破坏机制的重要反映，为研究不同加载速率对砂岩弯曲破坏的影响，通过三点弯曲实验和扫描电镜方法，对某煤矿关键层砂岩弯曲破断裂纹细观形态以及裂纹的自相似性进行了研究。选取6个不同加载速率对岩样进行三点弯曲实验，观察其宏观断裂情况，并利用扫描电镜对弯曲断裂面表面裂纹细观结构进行观察，并拍摄不同倍数下的扫描电镜图片。对图片进行图像处理后得到砂岩弯曲断裂破坏细观裂纹信息，并计算得到微裂纹的分形盒维数值。结果显示:随着加载速率的提高，砂岩穿晶断裂的比例也随之升高，裂纹分形维数亦随着加载速率的增大而增加，同时，分形维数还与弯曲断裂破坏荷载和抗弯强度成正比。可见，加载速率对断裂方式有一定的影响，且加载速率越大断裂所需的破坏能越大，裂纹分布越广，表明开采速度与岩爆等岩体动力灾变有密切关系。

Micro-mechanism of bending failure of sandstone under different loading rates

The micro morphology of rock rupture is an important reflection of rock failure mechanism, in order to study the effect of different loading rates on the bending failure of sandstone, the microscopic morphology of the bending breaking cracks and the self-similarity of the cracks are analysed by scanning electron microscope combined with three point bending test. Selecting six different loading rates to test the rock samples to observe the macroscopic fracture condition and then the microstructure of surface cracks on bend fracture surfaces is observed by scanning electron microscope, and take SEM pictures at different multiplier. After the image is processed, getting the micro crack information of bending fracture of sandstone, and the fractal box dimension value of the micro crack is calculated. The results show that the proportion of transgranular fracture increases with the increase of loading rate; the crack fractal dimension also increases with the increase of loading rate, and at the same time, the fractal dimension is proportional to the bending fracture load and bending strength. It can be seen that the loading rate has a certain effect on the fracture mode, and the greater the loading rate is, the greater the failure energy requires, and the wider the crack distribution is, indicating that mining speed is closely related to rock burst and other dynamic catastrophe of rock mass.