Abstract Full understanding of the compression and permeability behaviors of weakly anisotropic sandstones is a major challenge. The present work aims to address this challenging task through a series of triaxial compression tests equipped with permeability measurement on sandstone specimens to examine their mechanical properties and permeability evolution during the failure of weakly anisotropic rock. The influences of bedding angle and osmotic pressure are examined. It is revealed that when the bedding angle is lower than 30°, the strength decreases with an increasing angle and sliding fracture along the weak bedding occurs. When the bedding angle increases to 45°, the strength increases simultaneously accompanied by a mixed failure of cracks crossing the bedding and sliding along the bedding. When the bedding angle increases to 90°, the strength decreases as the angle increases, and cracks crossing the bedding dominates the failure. These phenomena indicate that under a certain osmotic pressure, the lower the bedding angle, the greater the influence of bedding on the strength. After loading, the degree of anisotropy for permeability is larger than that of strength as permeability is more sensitive to the distribution of cracks (i.e., the seepage channels), which is essentially controlled by the bedding orientations. Numerical simulations are also performed with the use of two-dimensional discrete element method, in which the numerical model is calibrated to match the stress-strain and permeability-strain responses of the experimental results. Simulation results reveal that concentrations of contact force chains appear near the shear band of the specimen, and the zones of sparse force chains are found in the surrounding areas. For the specimen with a larger bedding angle, the permeability when it fails increases faster than other orientations.

中文翻译：

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弱各向异性砂岩压缩渗透行为试验研究及离散元法建模

摘要 充分了解弱各向异性砂岩的压缩和渗透行为是一项重大挑战。目前的工作旨在通过一系列配备了砂岩试样渗透率测量的三轴压缩试验来解决这一具有挑战性的任务，以检查它们在弱各向异性岩石破坏过程中的力学性能和渗透率演变。检查了层理角度和渗透压的影响。结果表明，当层理角度小于30°时，强度随角度增加而降低，沿弱层理发生滑动断裂。当层理角度增加到45°时，强度增加的同时伴随着裂缝穿过层理并沿层理滑动的混合破坏。当层理角度增加到 90°时，强度随着角度的增加而降低，并且跨越层理的裂缝主导了破坏。这些现象表明，在一定的渗透压下，层理角越小，层理对强度的影响越大。加载后，渗透率的各向异性程度大于强度的各向异性程度，因为渗透率对裂缝（即渗流通道）的分布更敏感，这主要受层理方向的控制。还使用二维离散元方法进行数值模拟，其中校准数值模型以匹配实验结果的应力-应变和渗透-应变响应。模拟结果表明，接触力链集中出现在试样剪切带附近，并且在周边地区发现了稀疏的力链区域。对于层理角度较大的试件，其失效时渗透率的增加速度比其他方向快。