To understand the influence of shear on the hydraulic properties of rock fractures, shear-flow tests were carried out on rock fractures with different surface roughnesses. Each rough-walled fracture was replicated in four specimens, which were sheared at different displacements under normal stresses that varied from 0.5 to 2.0 MPa. At each shear displacement, a series of hydraulic tests with different hydraulic gradients were performed, and the nonlinear flow regimes of the fluid within the fractures were investigated. The results show that Forchheimer’s law can well describe the nonlinear relationship between the flow rate and the hydraulic gradient in rough-walled fractures. Both the linear coefficient and nonlinear coefficient decrease during shearing but increase as the normal stress increases. The critical hydraulic gradient increases with an increase in the shear displacement and normal stress. With an increase in the joint roughness coefficient, the critical hydraulic gradient decreases. The normalized transmissivity exhibits a strong correlation with the Reynolds number. As the shear displacement increases, the fitted curves of the normalized transmissivity versus the Reynolds number shift upward but the curves shift downward with an increase in normal stress. Additionally, the Forchheimer coefficient decreases with an increase in the shear displacement but increases with an increase in the applied normal stress. Visualization tests show that the number of flow paths is large when the shear displacement is small due to various distributions of the contact areas and that the flow of dyed water over the entire fracture decreases. As the shear displacement increases, the flow resistance decreases due to the shear dilation-induced increase in the aperture, and the advantage channel flow is distinct in the fracture. The contact ratio rapidly decreases as the shear displacement increases from 1 to 3 mm and then slightly varies with a continuously increasing maximum shear displacement of 9 mm.

中文翻译：

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剪切过程中流体在三维粗糙壁裂缝中非线性流动特性的实验研究

为了了解剪切对岩石裂缝水力特性的影响，对不同表面粗糙度的岩石裂缝进行了剪切流试验。每个粗糙壁裂缝都在四个试样中复制，在 0.5 到 2.0 MPa 的法向应力下以不同位移进行剪切。在每个剪切位移下，进行一系列不同水力梯度的水力试验，研究裂缝内流体的非线性流态。结果表明，Forchheimer定律可以很好地描述粗糙壁裂缝中流速与水力梯度之间的非线性关系。剪切过程中线性系数和非线性系数均减小，但随着法向应力的增加而增加。临界水力梯度随着剪切位移和法向应力的增加而增加。随着接头粗糙度系数的增加，临界水力梯度减小。归一化透射率与雷诺数有很强的相关性。随着剪切位移的增加，归一化透射率与雷诺数的拟合曲线向上移动，但随着法向应力的增加，曲线向下移动。此外，Forchheimer 系数随着剪切位移的增加而降低，但随着施加的正应力的增加而增加。可视化测试表明，由于接触面积的不同分布，当剪切位移较小时，流道数量较大，整个裂缝上的染色水流量减少。随着剪切位移的增加，由于剪切膨胀引起的孔径增加，流动阻力减小，裂缝中的优势通道流动明显。随着剪切位移从 1 毫米增加到 3 毫米，接触比迅速下降，然后随着最大剪切位移 9 毫米的不断增加而略有变化。