The inherent anisotropy of shale makes it exhibit different mechanical properties when measured in different directions. Generally, the measurements of the anisotropic mechanical properties of shale are generally conducted on cylindrical samples, and the computation of elastic constants is usually an empirical approximation. To accurately estimate the elastic parameters of shale rocks, an iterative method for approaching the crack initiation stress threshold was proposed in this work. Several uniaxial compression experiments were performed on cuboid Longmaxi shale samples with different bedding plane orientations. With a newly presented method, the apparent elastic modulus and Poisson’s ratios and five elastic constants were simultaneously determined. By examining the volumetric strain reversal point, the crack damage stress was obtained for each sample. The results demonstrate that the elastic regime, which was the range in which the elastic parameters were determined, significantly varies with bedding plane orientation. A transverse anisotropy ratio of 1.28 between in-plane modulus and out-of-plane modulus was determined for Longmaxi shale. Additionally, with the obtained elastic parameters, the energy releasing and dissipating behaviors of the samples during uniaxial loading were quantitatively characterized. The energy dissipation was found to rapidly increase once the crack damage stress was reached. However, before rock failure occurred, the total dissipated energy in each sample was very limited, indicating that microcrack propagation and rock damage were quite limited before rock rupture and that the shale samples were essentially destroyed by rapid energy release.

中文翻译：

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单轴压缩下龙马溪组页岩弹性及能量流各向异性表征

页岩固有的各向异性使其在不同方向测量时表现出不同的力学性能。一般而言，页岩各向异性力学性质的测量一般是在圆柱形样品上进行，弹性常数的计算通常是经验近似。为了准确估计页岩岩石的弹性参数，本文提出了一种逼近裂纹萌生应力阈值的迭代方法。对不同层理面方位的长方体龙马溪组页岩样品进行了多次单轴压缩实验。采用新提出的方法，同时测定表观弹性模量和泊松比以及五个弹性常数。通过检查体积应变反转点，获得每个样品的裂纹损伤应力。结果表明，弹性状态（弹性参数的确定范围）随层理面方向的变化而显着变化。龙马溪页岩的面内模量与面外模量之间的横向各向异性比值为 1.28。此外，利用获得的弹性参数，定量表征了单轴加载过程中样品的能量释放和耗散行为。一旦达到裂纹损伤应力，能量耗散就会迅速增加。然而，在岩石破裂发生之前，每个样品中的总耗散能量非常有限，这表明在岩石破裂之前，微裂纹扩展和岩石损伤相当有限，页岩样品本质上是被快速能量释放破坏的。