循环载荷下含水砂岩裂纹演化与损伤特征试验研究

基于矿井地下水库岩体频繁受到矿震、采动应力等循环荷载扰动这一工程背景，在实验室条件下开展了不同含水率砂岩单轴及循环加卸载试验，采用数字散斑技术，揭示了不同含水率砂岩裂纹扩展及破坏规律，基于电镜扫描微观分析，获得了循环载荷下不同含水砂岩微观劣化机制。试验结果表明：单轴及循环加卸载条件下，随着含水率增大，砂岩峰值强度均逐渐降低。干燥砂岩峰值轴向应变经历初始变形、等速变形、加速变形和失稳破坏4个阶段，含水砂岩经历初始变形、等速变形和失稳破坏3个阶段；随着含水率的增大，对应阶段内峰值轴向应变逐渐减小。通过变形率分析法验证发现，水对砂岩的变形记忆特性并无影响。单轴循环加卸载条件下，砂岩的破坏模式由干燥时的张拉?劈裂破坏逐渐向拉?剪混合破坏过渡，至饱和状态时呈现单一的剪切破坏。电镜扫描结果表明，随含水率增大，破裂结构面逐渐由光滑结构、浑圆状结构、片状结构向完全破碎结构过渡。随着含水率增大，绝对损伤参数不断增大，从侧面反映水岩耦合损伤的正相关性；累计损伤参数累积速率更快，同一循环周次下，累计损伤参数也更大。

Experimental study on crack evolution and damage characteristics of water bearing sandstone under cyclic loading

Based on the engineering background that rock masses of underground reservoirs in mines are frequently disturbed by cyclic loads such as mine earthquake and mining stress, uniaxial compression and cyclic loading tests for sandstones with different water contents were carried out in laboratory. The crack propagation and failure laws of sandstones with different water contents were revealed by digital speckle technique. Based on SEM micro analysis, the micro deterioration mechanism of sandstones with different water contents under cyclic loading was obtained. The test results show that the peak strength of sandstone decreases gradually with the increase of water content under both uniaxial compression and cyclic loading conditions. The peak axial strain variation of dry sandstone experiences four stages of initial deformation, constant velocity deformation, accelerated deformation, and instability failure, and that of the water bearing sandstone experiences three stages of initial deformation, constant velocity deformation, and instability failure. With the increase of water content, the peak axial strain in the corresponding stage gradually decreases. It is verified by the deformation rate analysis method that water has no effect on the deformation memory characteristics of sandstone. Under uniaxial cyclic loading condition, the failure mode of sandstone gradually transits from tension–splitting failure at dryness to tension–shear mixed failure, and presents a single shear failure at saturation. SEM results show that with the increase of water content, the fracture structure plane gradually transits from smooth structure, round structure, and sheet structure to completely broken structure. With the increase of water content, the absolute damage parameter increases, which reflects the positive correlation of water–rock coupling damage, and the cumulative damage parameter larger at the same cycle accumulates faster.