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An Analytical Microcrack-Based Rock Model with Implications for Earthquake Mechanisms Induced by Stress Changes
Mathematical Geosciences ( IF 2.6 ) Pub Date : 2020-03-02 , DOI: 10.1007/s11004-020-09857-2
Xiaozhao Li , Chengzhi Qi , Liren Ban , Zhushan Shao

Abstract

Shear fracture triggered by subcritical crack extension in intact brittle rocks under long-term compressive loading plays a significant role in the evaluation of earthquake mechanisms. Changes in external loading strongly influence the subcritical crack growth of intact rocks during earthquake nucleation. An important conundrum is how to establish the relationship between shear fracture induced by subcritical crack growth and external loading path in brittle rocks under lithospheric conditions. A novel micromechanical method that introduces shear fracture behavior is proposed to predict the time-dependent shear properties induced by the subcritical cracking of brittle rocks when the initial state of rocks starts from the peak point of the stress–strain curve measured by the conventional triaxial compressive test. This approach is developed on the basis of the wing crack model, subcritical crack growth law, and Mohr–Coulomb strain-softening model. The effect of loading and unloading paths on the evolution of shear properties of rocks under lithospheric conditions is analyzed by drawing a function of historical stress. The corresponding evolution of strain, shear strength, cohesion, and internal friction angle caused by subcritical crack growth under different stress paths is studied. Cohesion and shear strength continuously undergo a weakening process, and the internal friction angle initially undergoes a strengthening and, finally, a weakening process during subcritical crack growth under constant compressive loadings. The effect of the sudden change in axial stress on shear strength is smaller than that of the sudden change in confining pressure. A sudden decrease in confining pressure causes a rapid drop in shear strength, leading to a dramatic rise and drop in the rate of shear strength. Implications for evaluating earthquake mechanisms triggered by stress changes from the evolution of shear properties caused by subcritical crack growth in brittle rocks are also proposed.



中文翻译:

基于微裂纹的解析岩石模型,对应力变化引起的地震机制具有影响

摘要

在长期压缩载荷下,完整脆性岩石中亚临界裂纹扩展引发的剪切断裂在评估地震机制中起着重要作用。在地震成核过程中,外部载荷的变化强烈影响完整岩石的亚临界裂纹扩展。一个重要的难题是如何在岩石圈条件下建立亚临界裂纹扩展引起的剪切断裂与脆性岩石的外部载荷路径之间的关系。提出了一种引入剪切断裂行为的新型微力学方法,以预测当岩石的初始状态从常规三轴压缩测量的应力-应变曲线的峰值开始时,脆性岩石的亚临界裂纹诱导的随时间变化的剪切特性。测试。该方法是基于机翼裂纹模型,亚临界裂纹增长规律和Mohr-Coulomb应变软化模型开发的。通过绘制历史应力函数,分析了加载和卸载路径对岩石在岩石圈条件下剪切特性演化的影响。研究了在不同应力路径下亚临界裂纹扩展引起的应变,剪切强度,内聚力和内摩擦角的演变。内聚力和剪切强度持续经历弱化过程,并且在恒定压缩载荷下,在亚临界裂纹扩展过程中,内摩擦角首先经历了强化过程,最后经历了减弱过程。轴向应力的突变对剪切强度的影响小于围压的突变。围压的突然降低导致剪切强度迅速下降,导致剪切强度速率急剧上升和下降。还提出了评估应力变化触发的地震机制的意义,这些应力变化是由脆性岩石中的亚临界裂纹扩展所引起的剪切特性的演化引起的。

更新日期:2020-04-13
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