考虑岩石剪切局部化细观特征的Mohr—Coulomb强度修正准则

It is known to all that shear localization is a precursor to rock failure. The famous Mohr-Coulomb (MC) failure criterion, however, cannot explain this phenomenon when it was applied to relative geology disasters’ investigations. This application aims to a new modification of MC criterion by shear band width through a thorough survey of shear localization band during rock deformation and destabilization on meso-structure level. The new MC criterion, concluding the width of shear band, is firstly held out based on previous results by myself and meso-physical mechanism of material, with dimensional analysis. It also studies relationship between the shear band width and rock’s meso-structure. Secondly, the applicant is about to find a “precise” method to measure the shear band width. To accomplish this target, it carries out series experiments of rocks of all kinds and under different loading conditions, with width observations by methods such as particle image velocimetry (PIV), scanner of electronic microscope (SEM) and the monitoring and localization of acoustic emission (AE). Finally, factors that influenced shear band width are studied. Based upon mechanical experiments and a systematical investigation to rock’s meso-structure, it is looking for factors that influenced the shear band width through meso-structure and founding their quantitative relation with shear band width. It can be help to find the AE precursor of rock failure. The new modified MC criterion can give a more reasonable explanation to relative phenomenon of geology disasters and be applicable to more complex engineering geological conditions.

剪切局部化是岩石变形破坏的前兆，Mohr-Coulomb（MC）强度准则在用于地质灾害研究时，不能解释岩石的剪切局部化现象。本项目拟在细观结构层次研究岩石变形失稳的剪切局部化特征，用剪切带宽度对MC强度准则进行修正。首先，基于已做的研究成果及材料细观物理机制，运用量纲分析，推导含剪切带宽度的MC强度准则，确定剪切带宽度与材料微细观结构参数的关系。其次，利用粒子图像测速技术（PIV）、扫描电镜观测（SEM）和声发射（AE）监测定位结合，研究不同结构类型岩样在各种加载条件下的剪切带特征，建立“准确”测量剪切带宽度的实验方法。最后，研究剪切带宽度的影响因素。结合力学实验及岩石细观结构的系统分析，确定与岩石细观结构相关的各因素对剪切带宽度的影响，建立它们与剪切带宽度之间的定量关系，确定岩石破坏的声发射前兆。修正的MC强度准则，可以更好地解释各种相关的地质灾害现象，适用于更为复杂的工程地质条件。

项目完成了对传统Mohr-Coulomb强度准则的剪切局部化修正，通过Zhukov公式推导得到了较为准确的剪切局部化带宽度理论计算公式，将影响强度的温度、应变率、气体吸附等因素通过剪切带宽度嵌入MC强度准则，拓宽了MC强度准则在各种工程地质环境下的适用性，用实验数据进行了定性验证。. 通过不同岩性单轴压缩实验，利用纵应变、体应变、裂隙应变等将岩石应力应变曲线划分为七个不同的阶段，从声发射事件累积曲线、频率时间散点图、相关系数及相关长度、空间分布特征等多个方面的组合，可以独立确认岩石全应力应变曲线的各个阶段，将残余段根据声发射特征重命名为余震段。类似于地震弹性回跳理论，岩样峰前软化段的构造集聚形成剪切局部化，导致了峰后应力跌落主破裂的发生，声发射由弹性能释放造成的裂隙损伤过程激发，峰前软化段的声发射特征（AE大平台、AE阶梯，纵向AE主频线变稀疏、变贯通，相关AE数及相关长度出现峰值，多区加密集聚型，相关长度出现峰值）可以作为岩石破坏前兆。. 按力学性质，将岩石细观结构按照颗粒结构、排列方式、胶结强度、缺陷类别，综合划分为162类，结合岩石细观破坏方式，用便携式显微镜研究了岩石损伤的细观机制。基本可以确定，宏观可见弱胶结节理或其它面缺陷是控制岩石破坏方式的重要因素之一，它将在与剪切带分布的方向上起主导作用；细小的强颗粒、微少的弱颗粒等形成的细观微小缺陷、已重新强胶结的缺陷、与最大主应力方向接近的缺陷几乎不影响宏观破裂路径，在无明显缺陷应力集中影响的情况下，应力状态起主导作用，多数岩样呈现常见的锥形破坏。声发射的激发起源于这些细观裂隙过程。