Understanding the shear-flow-transport processes in rock fractures is one of major concerns for many geo-engineering practices, yet the effect of shear direction change on the flow and transport properties through rough-walled rock fractures has received little attention. In this study, a series of shear tests on artificial fractures with different surface roughness are conducted, in which the shear direction is altered perpendicularly. The distribution of apertures and its evolution during shearing are evaluated, which are further applied to simulate fluid flow and solute transport through fractures in the directions parallel and perpendicular to shear direction using a finite element method code. The effect of shear direction change on flow and transport properties of rock fractures is systematically investigated. The results show that when the shear direction is changed perpendicularly during shearing, the normal displacement changes from increasing (i.e., dilation) to decreasing (i.e., closure) with increasing shear displacement. The final normal displacement depends on the competition between dilation and closure induced by the shear in two directions, which directly determines the aperture distribution thereby affecting the flow and transport processes through fractures. The closure is more significant for the fracture with a smaller JRC, resulting in a more dramatic decrease in equivalent permeability. The historical shear stress can either promote or block the solute transport depending on the distributions of void spaces and contact obstacles induced by shearing in two perpendicular directions. The Peclet number decreases during shearing in spite of the magnitude of historical shear displacement, indicating that the dispersion becomes much significant with shearing due to the increasingly concentrated contact areas and flow channels.

中文翻译：

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单条粗壁岩裂缝剪切方向变化对剪切流输运过程的影响

了解岩石裂缝中的剪切流输运过程是许多地球工程实践的主要关注点之一，但剪切方向变化对通过粗糙壁岩石裂缝的流动和输运特性的影响很少受到关注。在这项研究中，对不同表面粗糙度的人工裂缝进行了一系列剪切试验，其中剪切方向垂直改变。评估了剪切过程中孔隙的分布及其演变，并进一步应用于模拟流体流动和溶质在平行和垂直于剪切方向的方向上通过裂缝的输运，使用有限元方法代码。系统地研究了剪切方向变化对岩石裂缝流动和输运特性的影响。结果表明，当剪切过程中剪切方向垂直变化时，法向位移随剪切位移的增加而由增加（即膨胀）变为减少（即闭合）。最终的法向位移取决于两个方向剪切引起的膨胀和闭合之间的竞争，它直接决定了孔径分布，从而影响通过裂缝的流动和输运过程。对于 JRC 较小的裂缝，闭合更为显着，从而导致等效渗透率更显着降低。历史剪切应力可以促进或阻止溶质传输，这取决于空隙空间的分布和由两个垂直方向剪切引起的接触障碍。