Low Static Shear Modulus Along Foliation and Its Influence on the Elastic and Strength Anisotropy of Poorman Schist Rocks, Homestake Mine, South Dakota
Low Static Shear Modulus Along Foliation and Its Influence on the Elastic and Strength Anisotropy of Poorman Schist Rocks, Homestake Mine, South Dakota
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DOI：
10.1007/s00603-020-02182-4
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发表时间：
2020-08-09
影响因子：
6.2
通讯作者：
Wang, Herbert F.
中科院分区：
文献类型：
--
作者：
Condon, Katherine J.;Sone, Hiroki;Wang, Herbert F.
研究了片理取向和细尺度褶皱对Poorman片岩静、动弹性特性和无侧限强度的影响。来自三轴和单轴实验室实验的测量结果揭示了静态和动态杨氏模量的显著变化，这取决于相对于片理平面的样品方向。横向各向同性介质的动态p波模量和s波模量在平行于片理面方向上更硬，epsilon和gamma的平均Thomsen参数分别为0.133和0.119。静态杨氏模量在21 ~ 117 GPa之间变化显著，当对称轴（x(3)-轴）斜面向加载方向时，观察到一个特殊的趋势，即一些片理样品组的静态杨氏模量出现异常下降。利用横向各向同性介质的应力和应变关系，我们推导出杨氏模量作为弹性模量lie(1)、E-3、nu（31）和g（13）的函数和样品方向的解析表达式，以拟合静态杨氏模量测量值。将方程与杨氏模量数据进行回归，发现在斜对称轴方向上的静态杨氏模量的降低直接受到低剪切模量G（13）的影响，我们将其归因于当叶理面受到剪切应力作用时，在静态变形过程中沿着叶理面发生的剪切滑动。我们认为这种动静各向异性的差异是近零孔隙度各向异性岩石的特征。单轴抗压强度在21.9 ~ 194.6 MPa之间变化显著，当对称轴方向与加载方向为45°或60°时，单轴抗压强度最低，这也是静态变形过程中沿理面剪切滑动的结果。
We investigate the influence of foliation orientation and fine-scale folding on the static and dynamic elastic properties and unconfined strength of the Poorman schist. Measurements from triaxial and uniaxial laboratory experiments reveal a significant amount of variability in the static and dynamic Young's modulus depending on the sample orientation relative to the foliation plane. Dynamic P-wave modulus and S-wave modulus are stiffer in the direction parallel to the foliation plane as expected for transversely isotropic mediums with average Thomsen parameters values 0.133 and 0.119 for epsilon and gamma, respectively. Static Young's modulus varies significantly between 21 and 117 GPa, and a peculiar trend is observed where some foliated sample groups show an anomalous decrease in the static Young's modulus when the symmetry axis (x(3)-axis) is oriented obliquely to the direction of loading. Utilizing stress and strain relationships for transversely isotropic medium, we derive the analytical expression for Young's modulus as a function of the elastic moduliE(1),E-3,nu(31), andG(13)and sample orientation to fit the static Young's modulus measurements. Regression of the equation to the Young's modulus data reveals that the decrease in static Young's modulus at oblique symmetry axis orientations is directly influenced by a low shear modulus,G(13), which we attribute to shear sliding along foliation planes during static deformation that occurs as soon as the foliation is subject to shear stress. We argue that such difference between dynamic and static anisotropy is a characteristic of near-zero porosity anisotropic rocks. The uniaxial compressive strength also shows significant variability ranging from 21.9 to 194.6 MPa across the five sample locations and is the lowest when the symmetry axis is oriented 45 degrees or 60 degrees from the direction of loading, also a result of shear sliding along foliation planes during static deformation.