不同粒径黄砂岩微观−宏观裂纹演化机制研究

为了探讨粒径对黄砂岩微观-宏观裂纹演化机制的影响，系统地开展了不同粒径黄砂岩单轴压缩声发射试验。基于声发射监测技术以及震源机制反演方法，对岩石变形破坏过程中微裂纹演化机制进行了研究，同时利用电镜扫描技术与几何分形理论，对破坏后的砂岩表面裂隙宏观形态及试件断口的微观形貌特征进行了分析。试验结果表明：粒径的大小、胶结物类型的不同均可影响岩石强度，通过室内试验得出随着黄砂岩粒径的逐渐增大，其峰值应力呈逐渐下降的变化趋势；对比不同粒径黄砂岩试件变形破坏过程中的声发射改进 b 值（ bI 值）与平均声发射能率，所有试件峰值破坏前平均声发射能率均存在“激增”与“激降”现象，且声发射 bI 值在砂岩试件达到峰值破坏时下降到最小值，该现象可以作为岩石的失稳破坏前兆特征；随着构岩矿物颗粒粒径的增大，岩石内部微裂纹的破坏模式由张拉型为主导向剪切型为主导进行转变；破坏后岩样表面宏观裂隙的分形维数随着岩石粒径的增加呈现下降的变化趋势，即粒径大小对岩石表面宏观裂隙演化过程具有一定控制作用。

Microscopic-macroscopic crack evolution mechanism of yellow sandstone with different particle sizes

In order to investigate the influence of particle size on the micro-macro crack evolution mechanism of yellow sandstone, uniaxial compression acoustic emission tests on yellow sandstone with different particle sizes were carried out systematically. Based on acoustic emission monitoring technology and focal mechanism inversion method, the evolution mechanism of microcracks in the process of rock deformation and failure was studied. Meanwhile, the macroscopic morphology of surface cracks and the microscopic morphology characteristics of specimen fracture were analyzed by scanning electron microscope and geometric fractal theory. The test results show that the size of the particle size and the type of cement can affect the strength of the rock. The laboratory test shows that the peak stress of the yellow sandstone decreases with the gradual increase of the particle size. By comparing the bI values (improved b values) and average acoustic emission energy of different sizes of yellow sandstone specimen in the deformation damage process, it was found that before the peak failure of all specimens, the average acoustic emission energy rate had phenomenon of "surge" and "plunge", and the bI values dropped to the minimum value when the sandstone specimen reached the peak failure, this phenomenon could be regarded as a precursor of rock instability and failure. The failure mode of microcracks in the rock changed from tension-oriented to shear-oriented as the mineral particle size increased. After failure, the fractal dimension of macroscopic fractures on rock surface decreased with the increase of rock particle size, that is, particle size has a certain control effect on the evolution process of macroscopic fractures on rock surface.