砂岩多步压剪的声发射特性研究

Study on Acoustic Emission Characteristics of Sandstone under Multi-step Compression and Shear Tests

为了了解砂岩多阶段性应力分布特征,进行了多步压剪实验,加载速率分别为0. 02kN/s、0.1 k N/s、0.5 kN/s,并同步采集全过程声发射信号。利用最大似然估计法分析了声发射能量统计分布特征,结果表明:(1)多步压剪试验的能量概率密度函数符合幂定律分布,并满足能量上的幂律无尺度分布;(2)加载阶段与恒压阶段声发射信号量相差较大,跨越能量数量级有所不同,但加载、恒压阶段的概率密度函数与整体概率密度函数具有统一性,并可以用同一个幂值来表征;(3)加载阶段与恒压阶段幂值分布具有相似性,与概率密度函数形成良好对应;(4)恒压状态下的岩石具有流变特征,声发射能量信号在小能量区间服从线性分布;(5)加载后期,由于裂纹的扩展以及成核过程岩石会发生相变,此阶段能量概率密度函数与全过程保持一致,不受之前能量信号影响。

In order to understand the characteristics of multi-stage sandstone stress distribution,multi-step pressure-shear experiments were carried out. The loading rates were 0.02 k N/s,0.1 k N/s and 0.5 k N/s respectively,and during the whole process,acoustic emission(AE) signals were collected synchronously. The maximum likelihood method was used to study the statistical characteristics of AE energy and results showed that:(1) the probability density function(PDF) followed the power-law distribution for the energy.(2) AE signals had different orders of magnitude between the loading stage and the constant pressure stage,but the PDF of loading stage and constant pressure stage was consistent with the whole PDF,and therefore could be characterized by the same exponent.(3)the exponent distribution was similar for both loading stage and constant pressure stage,being in good accordance with the PDF.(4) The rock sample had rheological characteristics under constant pressure,and the AE energies were subject to linear distribution in small energy regions.(5) The rock sample went through a phase transition due to crack propagation and nucleation in the later stage of loading. The energy’s PDF was consistent with the whole process at that stage and was not affected by the previous energy signals.