基于三轴周期载荷声发射实验的煤岩疲劳损伤破坏机理及前兆特征

The strip pillar, room and pillar and various protective coal pillar would produce fatigue damage inevitably under the multiple repeated mining stress, the basic experiment study on triaxial cyclic loading and acoustic emission of coal is of has important meanings in theory and practice to deeply research fatigue damage mechanism and acoustic emission characteristics. Based on the study of reasonable triaxial cyclic loading acoustic emission experiment method, MTS815 servo-controlled rock mechanical test system is used to take experiments on coal samples under different cycle loading factors, the strength and deformation characteristics of coal fatigue damage would be revealed; then, analyzing the relationship between fatigue damage and energy dissipation, fatigue damage evolution model of coal would be established by using the acoustic emission parameters as damage variable, and the mechanism of coal fatigue damage would be revealed from different angles; additionally, comprehensively analyzing the acoustic emission precursor characteristics(criterion) of coal fatigue damage based on the deeply analysis of relationship between fatigue damage and mutation characteristics of acoustic emission precursory information such as characterization parameters, spectrum characteristic parameters and structure parameters; what’s more, according to the fractal and chaos characteristics of acoustic emission time series, reasonable method of nonlinear prediction of coal fatigue damage based on acoustic emission precursor characteristics(criteria) would be researched.

煤矿井下条带煤柱、房柱及各种保护煤柱在多次重复采动应力作用下必然产生疲劳损伤，开展煤岩三轴周期载荷声发射基础实验，深入研究煤岩疲劳损伤破坏机理及声发射前兆特征具有重要的理论及实际意义。课题拟在研究合理三轴周期载荷声发射实验方法的基础上，采用MTS815岩石伺服试验系统进行不同影响因素下的煤岩三轴周期载荷声发射试验，基于试验结果分析煤岩疲劳损伤破坏的强度及变形特征；探讨煤岩内部能量耗散与其疲劳损伤破坏演化关系，建立以声发射参数为损伤变量的煤岩疲劳损伤破坏演化模型，从不同角度深入揭示煤岩疲劳损伤破坏机理；在对声发射表征参数、频谱特征参数及构造参数等前兆信息的突变特征与疲劳损伤破坏相关关系深入研究的基础上，综合分析确定煤岩疲劳损伤破坏的声发射前兆特征（判据）；根据声发射时间序列的分形及混沌特征，研究基于声发射前兆特征（判据）的煤岩疲劳损伤破坏非线性预测方法。

煤炭地下开采过程中，房柱、条带煤柱和区段保护煤柱在重复采动应力作用下必定产生损伤累积，直至出现疲劳破坏失稳现象。系统研究煤岩疲劳损伤破坏演化过程中的力学机制及声发射前兆特征，对于采用声发射监测方法预测工程煤体的疲劳破裂失稳、保证煤矿安全高效生产具有重要理论指导意义。.课题采用将声发射检波器置于岩石力学试验系统三轴室之内合理声发射试验方法，对其疲劳损伤破坏演化机理及声发射前兆特征进行了系统研究，取得了以下主要成果和结论。. （1）随着应力水平的不断提高，轴向应变和环向应变均呈现出逐渐增加的发展态势。与单轴周期载荷试验相比，煤岩试样在三轴周期载荷下的不可逆应变呈现出更为缓和的发展变化特征。煤岩试样的弹性模量和损伤演化均呈现出明显的阶段性发展规律。除极限应力水平外，煤岩试样在周期载荷下的耗散能呈现出“L”型发展演化规律，而在极限应力水平则呈现出“U”型发展演化规律。. （2）探讨了应力水平和加载频率对声发射表征参数的影响，建立了基于声发射累计能量计数的疲劳损伤演化模型。. （3）初始应力水平阶段主要以拉伸裂纹为主，而后呈现出张剪复合破裂形式，临近疲劳破坏时声发射RA值出现陡增现象。与单轴周期载荷试验相比，三轴周期载荷下煤岩试样内部小尺度微破裂居多，声发射b值总体上呈现出相对稳定的发展变化规律。b值的突降可作为周期载荷下煤岩疲劳破坏的前兆特征。. （4）Hilbert边际谱中的声发射幅值随着应力水平的不断提高呈现出高频、中频、低频循序运移的发展态势。在极限应力水平阶段，声发射信号的“低频突升”可作为周期载荷下煤岩疲劳破坏的重要前兆信息。