Experimental study and discrete element method modeling of compression and permeability behaviors of weakly anisotropic sandstones
Experimental study and discrete element method modeling of compression and permeability behaviors of weakly anisotropic sandstones
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DOI：
10.1016/j.ijrmms.2020.104437
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发表时间：
2020-10-01
影响因子：
7.2
通讯作者：
Zhu, Yaoliang
中科院分区：
文献类型：
--
作者：
Yu, Jin;Yao, Wei;Zhu, Yaoliang
充分理解弱各向异性砂岩的压缩和渗透特性是一项重大挑战。本研究旨在通过对砂岩试样进行一系列配备渗透率测量的三轴压缩试验来应对这一挑战性任务，以检验弱各向异性岩石破坏过程中的力学性能和渗透率演变。研究了层理角度和渗透压的影响。结果表明，当层理角度小于30度时，强度随角度增大而降低，并沿软弱层理发生滑动断裂。当层理角度增大到45度时，强度同时增大，伴随有穿过层理的裂纹和沿层理滑动的混合破坏模式。当层理角度增大到90度时，强度随角度增大而降低，且穿过层理的裂纹在破坏中起主导作用。这些现象表明，在一定渗透压下，层理角度越低，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，因为渗透率对裂纹（即渗流通道）的分布更为敏感，而裂纹分布本质上受层理方向控制。还利用二维离散元方法进行了数值模拟，其中对数值模型进行了校准，使其与实验结果的应力 - 应变和渗透率 - 应变响应相匹配。模拟结果显示，接触力链集中出现在试样的剪切带附近，而稀疏力链区域出现在周边区域。对于层理角度较大的试样，其破坏时的渗透率比其他方向增加得更快。
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 degrees, the strength decreases with an increasing angle and sliding fracture along the weak bedding occurs. When the bedding angle increases to 45 degrees, 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 degrees, 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.