Abstract Frictional behaviour of joints/faults is of great importance in many geo-engineering applications across different scales. It is known that the joint surface roughness is one of the critical parameters controlling the frictional behaviour of rock joints. While nominal normal and shear stresses acting across the joint asperities are calculated based on overall shearing area, the actual normal and shear stresses can be much greater due to smaller actual contact area. The actual contact area on the other hand is known to be related to the joint surface roughness. In order to investigate the effect of contact area on the shear behaviour of rock joints, an extensive set of direct shear experiments at different normal stresses on dry and saturated shale, limestone and sandstone tensile joints were undertaken. To compare the frictional properties of natural and artificial samples, synthetic samples were also fabricated, and their frictional properties were evaluated. Results of this study revealed that the predominant parameter controlling the frictional strength is the actual contact area. While the common models in predicting the shear strength of rock joints were unable to fit the experimental data based on nominal contact area, the results based on actual contact area fit the measured values accurately. In addition, it was observed that when the actual contact area is considered, Mohr-Coulomb criterion is sufficient to fit the experimental data irrespective of the rock type, joint surface roughness or whether dry or saturated. This highlights that the Mohr-Coulomb criterion can appropriately predict the frictional strength if the actual contact area can be estimated. More importantly, the results showed that the surface roughness cannot dictate the shear behaviour of rock joints without considering the actual contact area.

中文翻译：

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接触表面积对干饱和岩石节理摩擦行为的影响

摘要 接头/断层的摩擦行为在许多不同尺度的地球工程应用中非常重要。众所周知，节理表面粗糙度是控制岩石节理摩擦行为的关键参数之一。虽然作用在接头粗糙面上的标称法向应力和剪应力是根据总剪切面积计算的，但由于实际接触面积较小，实际法向应力和剪应力可能要大得多。另一方面，已知实际接触面积与接头表面粗糙度有关。为了研究接触面积对岩石节理剪切行为的影响，在干燥和饱和的页岩、石灰岩和砂岩拉伸节理上进行了大量不同法向应力下的直接剪切实验。为了比较天然和人造样品的摩擦性能，还制作了合成样品，并评估了它们的摩擦性能。这项研究的结果表明，控制摩擦强度的主要参数是实际接触面积。常用的岩石节理抗剪强度预测模型无法拟合基于名义接触面积的实验数据，而基于实际接触面积的结果与实测值吻合。此外，观察到当考虑实际接触面积时，Mohr-Coulomb 准则足以拟合实验数据，而不管岩石类型、节理表面粗糙度或干燥或饱和状态。这突出表明，如果可以估计实际接触面积，则 Mohr-Coulomb 准则可以适当地预测摩擦强度。更重要的是，结果表明，如果不考虑实际接触面积，表面粗糙度不能决定岩石节理的剪切行为。