不同卸载速率下岩爆破坏特征试验分析

Rockburst characteristics based on experimental tests under different unloading rates

对北山花岗岩进行4种不同速率卸载的岩爆试验,收集试验后产生的碎屑,进行粒径分布和基本尺寸量测,得到碎屑尺度特征。利用声发射系统采集试验过程中声发射信号,采用典型的时频分析手段,提取每一个声发射波形信号的主频值,绘制整个试验全局主频分布图,找到花岗岩岩爆主频分布带。试验结果表明:随着卸载速率的降低,碎屑总数量,块状、板状碎屑所占百分比均呈下降趋势。而声发射分布带主要位于中低频带内,且随着卸载速率降低逐渐上移,由密集变离散。根据声发射参数RA和AF特征值分布情况,结合核心密度定义,揭示裂纹类型演化过程。发现在卸载岩爆过程中产生了大量张拉裂纹和一定量的剪切裂纹,随着卸载速率的降低,声发射信号量减少,预示着岩石内部裂纹数量明显减少。以上室内试验结果对于认识不同卸载速率下岩爆机制具有重要意义,同时为工程实际中通过调整开挖速率降低岩爆风险的可行性提供了室内试验支持。

This paper presents the experimental study of the granite rockburst under four different unloading rates. With the help of the collected fragments measurement after tests, the scale features of fragments can be obtained. Acoustic emission system is used to monitor the internal damage of the rock;and the typical time-frequency analysis tool is applied to the major frequency extraction of every acoustic emission （AE） waveform. The tested results indicate that the total number of fragments and the portion of fragments with blocky structure and plate shape have a decreasing trend with the unloading rate dropping down. The AE major frequency band is found to be located in the moderate low frequency band and it is up-shifting as the unloading rates decrease changing from intensive broadband to discrete narrowband. According to the distribution of RA and AF, the crack type evolution can be determined. During the unloading rockburst test, the cracks generating in the specimen are mainly tensile cracks. Further decreases in unloading rate do appear to drive the AE signals reduced indicating crack amount decrease. All these results will be helpful for us to understand the rockburst mechanism under different unloading rates and prove the feasibility of adjusting excavation speed to reduce rockburst risk in field site.