电脉冲循环冲击作用对花岗岩抗剪性能弱化研究

Weakening of shear strength of granite with cyclic shock of electrical pulse

为探究坚硬岩体在高压电脉冲循环冲击作用下的致裂效果,开展花岗岩高压电脉冲循环冲击后的直剪试验,研究冲击次数对抗剪强度和裂纹扩展的影响规律。研究结果表明:花岗岩试样内部损伤程度随冲击次数增加而逐步累积,5 kV电压条件下,前3次冲击作用在试样内部几乎无新裂纹产生,冲击4次后试样内部开始萌生微小裂纹,并最终扩展形成贯穿裂缝;冲击4,5和6次后,试样内部损伤面积占比依次增加至6.65%,66.72%和70.80%;抗剪强度随冲击次数增加不断弱化,与未受冲击试样相比,冲击6次后试样抗剪强度弱化71.59%,剪切过程中声发射振铃计数降低58.41%,累积能量降低82.85%;声发射(AE)累积能量呈现出明显的“平静期—缓慢增加期—急速增加期”阶段变化特征;当冲击无明显裂纹产生时,试样剪切载荷加载过程中平静期延长,缓慢增加期缩短;当产生明显裂纹后,平静期缩短,缓慢增加期延长;冲击后,试样均在急速增加期呈现出更活跃的声发射信号,可以将声发射信号的突变作为试样剪切破坏的前兆,声发射事件点空间演化分布呈现出“抗剪破坏所需外部能量更低且声发射信号提前”的特征。

In order to investigate the cracking effect of high voltage electric pulse cyclic impact on hard rock mass,direct shear tests after high voltage electric pulse cyclic impact on granite were carried out to study the effect of impact number on shear strength and crack propagation.The results show the internal damage degree of granite samples accumulates gradually with the increase of the number of shocks.Under the condition of 5 kV,there are almost no new cracks in the sample with the first three shocks.After the fourth shocks,micro cracks begin to sprout and eventually expand to form penetrating cracks.After the fourth,fifth and sixth shocks,the damage area ratio increases successively to 6.65%,66.72%and 70.80%,respectively.The shear strength weakens with the increase of the number of shocks.Compared with the samples without impact,the shear strength weakens by 71.59%after 6 shocks,the acoustic emission ringing count decreases by 58.41%and the cumulative energy decreases by 82.85%during the shear process.The accumulated acoustic emission(AE)energy shows an obvious change characteristic of"quiet period−slow increase period−rapid increase period".When no obvious crack is generated during the impact,the quiet period increases and the slow increase period shortens during the shear loading process.When obvious cracks occur,the calm period is shortened and the slow increase period is prolonged.After impact,all the samples show more active AE signals in the period of rapid increase,and the abrupt change of AE signals can be taken as the precursor of shear failure of the samples.The spatial evolution distribution of AE event points shows the characteristics of"lower external energy required for shear failure and advanced AE signals".