含裂隙砂岩破裂特征及微震和电荷感应信号规律试验研究

Tests for fracture characteristics of fractured sandstone and micro-seismic and charge induced signal laws

为了有效提取含裂隙砂岩失稳破坏的前兆信息,用试验方法研究了单轴压缩条件下完整砂岩和不同倾角裂隙砂岩的破坏特征及电荷感应信号和微震信号的规律。结果表明,裂隙的存在成为影响砂岩的单轴抗压强度和破坏特征的主要因素,随着裂隙倾角的减小,砂岩的单轴抗压强度会降低,破裂形式由拉剪复合破裂向剪切滑移破裂转变。完整试样微震与电荷信号只有在峰值应力附近出现高幅值波动,在加载初期压密阶段和弹性阶段信号较低;含裂隙岩样微震与电荷高幅值信号出现时间提前,高幅值脉冲数增多,且高幅值脉冲从完整试样只出现在峰值应力附近,到有裂隙时在岩石弹性后期出现多个高幅值脉冲数转变。当裂隙倾角由60°→45°→30°变化时,微震与电荷信号由开始的密集型信号向多个孤立型信号转变。微震信号与电荷信号并不是完全同步的,在岩石峰后阶段才有较好的"协同性"信号产生。岩石发生应力降是产生微震和电荷感应信号的充分非必要条件,将微震和电荷感应监测技术与岩体监测区域应力场分布结合指导现场实践有助于提高预测准确性和减少地质灾害的发生。

In order to effectively extract precursory information of instability failure of fractured sandstone,failure characteristics of intact sandstone and fissured one with different dips under uniaxial compression,and laws of charge induction signals and micro-seismic ones were tested and studied.Results showed that the existence of fractures is the main factor affecting uniaxial compressive strength and failure characteristics of sandstone;with decrease in fracture dip,the uniaxial compressive strength of sandstone decreases,and the fracture mode changes from tension-shear composite fracture to shear-lip one;micro-seismic and charge signals of intact specimens have high amplitude fluctuation only near peak stress,but they are lower in initial loading compaction stage and elastic one;if the occurrence time of micro-seismic and high-amplitude charge signals in fractured rock samples is in advance,the number of high-amplitude pulses increases;high-amplitude pulses only appear near peak stress in intact samples,if rock specimens have fractures,many high-amplitude pulses appear in rock elastic later stage;when fracture dip angle changes from 60°to 45°and then to 30°,micro-seismic and charge signals change from intensive ones to multiple isolated ones,micro-seismic signal and charge one are not completely synchronized,and better"synergistic"signals appear only in rock post-peak stage;stress drop of rocks is a sufficient and unnecessary condition to generate micro-seismic and charge-induced signals;combining micro-seismic and charge induction monitoring technique with stress field distribution of rock mass monitoring area to guide field practice is helpful to improve the prediction accuracy and reduce the occurrence of geological disasters.