Abstract:

This study examines the impact of in-situ stress and mining-induced disturbances on fault stability, specifically focusing on the influence of micro-crack density on the fault stick-slip instability process. The rock masses on the hanging wall and footwall of a fault are often characterized by micro-cracks, which alter their load-bearing structural system and thus influence the fault's sliding behavior, leading to various failure modes. Therefore, understanding the mechanical behavior and damage patterns associated with fault stick-slip instability under different micro-crack densities is essential. Acoustic emission(AE)monitoring, a critical tool for studying fault stick-slip failure, provides valuable information on fault activation. However, the fault structure constrains AE wave propagation paths and intensity, limiting insights into the interaction between fault planes and surrounding rock masses.

The study uses the Particle Flow Code(PFC), a discrete element method(DEM)simulation governed by force-displacement laws and Newton's second law, to model and analyze fault stick-slip instability. PFC simulates the motion and interaction of rigid particle assemblies, representing material fracture, damage, and crack propagation. In this framework, particle contact models define the mechanical properties of particle assemblies. The study constructs discrete element numerical models under varying micro-crack densities to simulate the stick-slip process of faults. By monitoring mechanical behavior at particle contacts, the study provides insights into the AE characteristics and evolutionary patterns of fault stick-slip. The AE system, constructed via the moment tensor method, reveals micro-fracture interactions within the rock mass and enables identification of fracture types and the spatio-temporal distribution of AE events. During fault stick-slip instability, the moment tensor represents the displacement generated by contact forces on particles, akin to the effect of body forces. By tracking displacement and force changes during particle-bond fracture, the moment tensor is calculated based on contact forces within the fracture region.

Key findings reveal that different micro-crack densities significantly influence the fault stick-slip instability process. The results detail stress-strain relationships(e.g., stick-slip event frequency, onset stress, stress drop at onset, and maximum stress drop)and AE signal evolution patterns. The fault stick-slip instability process can be divided into four stages, with numerous tensile micro-cracks generated near the fault surface. As micro-crack density increases, structural damage within the rock mass intensifies, reducing the fault's self-locking effect. This, in turn, affects fault stick-slip instability. Increased micro-crack density generally leads to a larger maximum stress drop, while onset stress drop tends to decrease. High micro-crack density also correlates with a higher frequency of minor stress drops in the latter stages of stick-slip.

In conclusion, this study provides valuable insights into the effects of micro-crack density on the fault stick-slip instability process, presenting a novel numerical simulation approach for examining fault activation mechanics. These findings offer a reference for laboratory AE experiments on fault stick-slip and contribute to field-based microseismic monitoring research.

Key words: fault stick-slip, acoustic emission, microcrack density, mechanical behavior

摘要：

在原岩应力及开采扰动作用下, 断层上、 下盘的岩体内部为微裂隙赋存状态, 改变了岩体的受力构架体系, 对断层上、 下盘滑动行为模型产生影响, 继而形成了不同的破坏模式。因此, 对不同微观裂隙密度下断层黏滑失稳运动过程的力学行为和损伤规律亟待开展进一步研究。声发射监测是研究断层黏滑破坏模型的重要手段, 可用来获取断层活化过程中的有效信息。然而, 断层结构面对岩体破裂声发射波的传播路径和强度造成了一定的阻碍, 从而在研究断层上、 下盘与岩体结构面的响应机制方面存在一定的局限性。文中采用离散元数值模拟方法构建了不同微观裂隙密度条件下的数值模型, 以模拟断层的黏滑失稳破坏过程。此外, 通过记录颗粒间接触的力学行为变化, 更深入地研究了断层黏滑的声发射特性和演化规律。研究结果详细地阐明了不同微观裂隙密度对黏滑失稳运动过程的影响, 包括应力-应变关系(如黏滑次数、 启滑应力、 启滑应力降和最大应力降)及声发射信号特征的演化规律。文中成果为深入理解岩体微观裂隙密度对黏滑失稳过程的影响提供了重要见解, 并为断层活化的力学行为研究提供了一种新的数值模拟方法。此外, 文中研究可作为室内断层黏滑声发射实验和现场微震监测研究的重要参考。

关键词: 断层黏滑, 声发射, 微观裂隙密度, 力学行为