瞬时应变型岩爆模拟试验中花岗岩主频特征演化规律分析

利用深部岩爆模拟试验系统对花岗岩进行室内瞬时岩爆模拟试验,同时利用声发射系统采集试验过程中声发射信号,得到试验全过程应力和声发射波形信息时域图。结合声发射累计能量曲线特征,找到5个关键拐点,即花岗岩初始加载能量激增后产生的第一个拐点A、岩爆发生前两次明显的上升台阶处拐点B和C、岩爆发生时的能量突跃点D、最终峰值点E。将关键点处波形信号从全时域波形中提取出来并进行快速傅里叶变换,得到各关键点二维功率谱图,结果表明:花岗岩声发射主频值在加载初期时为106 k Hz,随着荷载的增加,频率由低频向高频过渡,频带变宽且由单峰向多峰转化,频率成分复杂预示多种破裂模式的发生。岩爆前和最终岩爆时刻频带又变窄并恢复单峰,主频值降低至与初始加载时一致,约为106 k Hz,预示着岩爆时刻花岗岩岩石高能量的释放。

Feature evolution of dominant frequency components in acoustic emissions of instantaneous strain-type granitic rockburst simulation tests

This paper presents the experimental study of instantaneous strain-type granitic rockbursts. It uses the nondestructive acoustic emission (AE) testing method to monitor the rock internal damage during the simulation test. Using real-time waveform signals, we can plot the evolution of stresses and voltage signals in full time-domain. Combining with the cumulative AE energy curve, we can determine five key points which are the first inflection point A (positioned at initial load), the two turning points B and C (located at obvious rise ledges), the dramatic increasing point D and the final peak point E. The five points can be extracted and processed with the Fast Fourier Transform (FFT) in Matlab commercial software. The results indicate that the dominant frequency component of the granitic rock sample is 106 kHz at the initial loading stage. As the load increases, the frequency changes from low value to high value, the band of frequency becomes wider and wider, and the shape of wave changes from unimodal to multimodal. These frequency changes indicate the complicated frequency components and various fracture modes. At the time of rockburst occurring, the band of frequency becomes narrower and the shape of wave changes back to unimodal. The dominant frequency decreases to 106 kHz and equals to the initial value, which indicates a large amount of energy is released.