利用自主研发的煤岩剪切细观试验装置，以砂岩为研究对象，开展了不同饱和度数条件下的岩石剪切细观开裂演化与贯通机制试验研究，分析了砂岩剪切细观开裂演化过程和贯通机制，探讨了饱水系数对细观开裂和裂纹形态特征的影响。研究结果表明：剪切过程中，伴随着应力降，裂纹一般首先出现在剪切面中部，几条裂纹间断分布，距离较近的裂纹相互连通形成大裂纹，在应力继续下降的一瞬间，各裂纹连通形成贯通面；水的弱化作用影响了岩石的强度，使得试件底部出现较大的次级裂纹；饱水系数越大，分叉裂纹越多，使得试件的表面裂纹形态更加复杂，断裂面弯折段的数目越多，下端部次级裂纹越发育，整体损伤范围越大；细观上，局部独立裂纹贯通过程伴随着胶结颗粒岩桥的梁式旋转和弯曲折断，水的弱化作用，使得岩桥内部和外部微裂纹增多；随着饱水系数的增加，岩石剪切过程中出现的独立和次级裂纹的数目均呈增加趋势。

To investigate mesoscopic cracking propagation and coalescence mechanisms of rocks under shearing conditions, tests on sandstone samples are conducted using a self-developed mesoscopic test equipment. The effects of saturation degree on mesoscopic cracking and crack morphology are discussed. It is shown that in general cracks initially appear at the middle of the shear plane with stress dropping during the shearing process. Several cracks distribute discontinuously, and cracks within a short distance coalesce into large cracks. At the moment of stress dropping, all cracks connect with each other into a coalesced surface. The rock strength is affected by water weakening, which leads to large secondary cracks appearing at the bottom of specimens. When the saturation degree is higher, there are more bifurcation cracks appear around the main crack, and the specimen has more complicated surface patterns. When the number of fractured surface is increased, the secondary crack is growing slower and overall damage area is increasing faster. From the mesoscope aspects, the local independent crack coalescence process is accompanied by the beam rotation and bending fracture of the cemented rock bridge; the weakening effect of water results in the internal and external microcracks in the rock bridge increase. With the increase of saturation degree, the numbers of both independent cracks and secondary cracks show an increasing trend during shear process.