Clay-rich rocks are integral to subduction zone dynamics and of practical importance, for example, as barriers in nuclear waste and CO₂ repositories. While the effects of swelling strain on the self-sealing capabilities of these rocks are relatively well-established, the implications of polar fluids interacting with charged clay particles on the frictional behavior, and the role of swelling stress in initiating slip in critically stressed faults, remain ambiguous. To address these uncertainties, we conducted triaxial friction experiments using saw-cut samples, with the upper half composed of Opalinus claystone (OPA) and the lower half of Berea sandstone (BER). The frictional strength of the non-wetted OPA-BER interface was estimated based on experiments at confining pressures of 4–25 MPa and constant axial loading rate (0.1 mm/min). Fluid injection friction experiments were performed using decane (non-polar fluid) or deionized water (polar fluid) at 10 and 25 MPa confining pressures and constant piston displacement control. Macroscopic mechanical data were complemented by distributed strain sensing on the sample surface. Compared to decane, the frictional strength of the OPA-BER interface tended to decrease when injecting water, which is attributed to phyllosilicate lubrication and the transition of the OPA from a solid rock to an incohesive mud near the saw-cut surface. When injecting water, slip was initiated during initial hydration of the OPA-BER interface, although the apparent stress state was below the yield stress. To explain this behavior, we propose that the swelling stress is a crucial factor that should be integrated into the effective stress model.

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水-粘土相互作用对于富含粘土的岩石中断层滑动的重要性

富含粘土的岩石是俯冲带动力学的组成部分，具有实际重要性，例如，作为核废料和CO ₂储存库的屏障。虽然膨胀应变对这些岩石自密封能力的影响相对明确，但极性流体与带电粘土颗粒相互作用对摩擦行为的影响，以及膨胀应力在临界应力断层中引发滑动的作用，保持暧昧。为了解决这些不确定性，我们使用锯切样品进行了三轴摩擦实验，上半部分由蛋白石粘土岩（OPA）组成，下半部分由伯里亚砂岩（BER）组成。非润湿 OPA-BER 界面的摩擦强度是根据 4-25 MPa 围压和恒定轴向加载速率 (0.1 mm/min) 下的实验估算的。使用癸烷（非极性流体）或去离子水（极性流体）在 10 和 25 MPa 围压和恒定活塞位移控制下进行流体注入摩擦实验。宏观机械数据通过样品表面的分布式应变传感得到补充。与癸烷相比，注入水时 OPA-BER 界面的摩擦强度趋于降低，这是由于页硅酸盐润滑以及 OPA 从固体岩石转变为锯切表面附近的非粘性泥浆。当注水时，尽管表观应力状态低于屈服应力，但 OPA-BER 界面初始水合期间会引发滑移。为了解释这种行为，我们认为膨胀应力是一个关键因素，应该集成到有效应力模型中。