DISCRETE ELEMENT SIMULATION STUDY OF FAULT STICK-SLIP INSTABILITY PATTERNS AT DIFFERENT MICROCRACK DENSITIES
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.
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维普
