裂隙砂岩裂纹扩展声发射响应及速率效应研究

Macro-crack propagation process and corresponding AE behaviors of fractured sandstone under different loading rates

冲击地压等动力灾害是含裂隙结构面岩体破裂发育、成核的动态演化结果,借助声发射监测可精确感知破裂演化过程进而实现灾害的有效预警。测试不同加载速率下含平行贯通雁行裂纹砂岩声发射行为的全程动态时变演化规律,借助声发射三维定位重点分析裂纹扩展关键特征点处声发射时–空–频–非线性响应及其加载速率效应。结果表明:(1)裂隙砂岩裂纹扩展及声发射响应行为存在着明显的加载速率效应:随着加载速率增大,声发射计数峰值、多重分形谱宽度Δα及主频幅值均逐渐增大,Δf(α)和主频则逐渐减小,岩体破裂过程的动力显现及非线性特征也越来越明显,破裂模式也由剪切破坏过渡为张拉破坏。(2)裂隙砂岩受载全程中随着应力增大声发射计数、分形谱宽度Δα、主频幅值及低频成分占比逐渐增大,多重分形参量Δf(α)逐渐减小;特别在亚失稳阶段,声发射计数表现出多次"突增+平静"特征,频谱及多重分形参数表现出波动特性,可以根据声发射信号动态时变趋势和"突增+平静"特征对动力灾害做出临灾预警。(3)裂隙砂岩宏观裂纹起裂、扩展形成主破裂过程就是锁固体不断破裂的过程,每一次锁固体断裂均对应着宏观裂纹发育、应力突降、声发射计数高值响应、频谱及多重分形参数极值。基于微破裂演化成核多锁固体破裂理论定量地解释裂隙砂岩力学性质的加载速率效应及亚失稳阶段声发射信号几起几落的"突增+平静"前兆行为。

The geodynamic disaster is the process of development and nucleation of fractured structures in rock mass. With the aid of acoustic emission（AE） monitoring,the failure process can be monitored to realize the accurate early-warning of the disasters. In this paper,the AE response varying with time including the AE counts,multifractal and frequency spectrum of fractured sandstone were measured in the entire loading process under different loading rates. The AE behaviors at the key points of crack propagation and the loading rate effects were studied using 3D locating according to the AE events. The loading rate was found to have significant effects on the propagation of macro-cracks and AE behaviors of fractured sandstone. The peak AE counts,the multifractal spectrum width Δα,and the amplitude of dominant frequency increase gradually but the dominant frequency and multifractal Δf（α） decrease gradually with the increasing of loading rates. The dynamic and nonlinear characteristics of rock failure process become more obvious,and the failure modes change from shear failure to tensile failure. In the whole loading process,the AE counts,the multifractal spectrum width Δα and the low frequency component proportion increase gradually,while the multifractal parameter Δf（α） decreases gradually with the increasing of axial stress. The AE multifractal and spectral parameters show fluctuation characteristics,and the AE counts show＂pulse ＋ calm＂feature for multiple times when the sandstone specimen enters into the meta-instable stage. These time-varying trends of AE can be used to early-warn the dynamic disaster. The initiation,propagation,coalescence and nucleation of macro-cracks are the processes of rupture of locked bodies inside rock. An event of fracturing of locked body corresponds to a drop of stress,a large value of AE count,and an extremum value of the multifractal and spectral parameters. The loading rate effects and the AE response precursor behaviors of repeated suddenly increasing then quiet at the meta-instable stage can all be explained reasonably with the established theory of rupture nucleation of multiple locked bodies.