干湿循环作用下弱胶结岩石声发射特征试验研究

Experimental study on acoustic emission characteristics of weakly cemented granular rocks affected by dry-wet cycling process

弱胶结岩石具有强度低、胶结弱、易风化、易水解和含水丰富等特点,针对干湿循环作用后引发工程岩体失稳的问题,通过弱胶结岩石单轴压缩试验和AE监测技术,对比分析了不同干湿循环作用次数后的岩样的变形破坏特征及破坏过程中声发射事件数、能量释放率、b值及熵值等参数的变化特征。研究结果表明:在干湿循环作用下弱胶结岩石强度劣化效应明显,弱胶结岩石到达峰值强度时轴向应变明显增加;不同干湿循环作用下弱胶结岩石破坏过程中声发射事件数和能量释放率变化趋势一致,在初始阶段较少,弹塑性阶段缓慢增加,峰值阶段达到最大值,而对于声发射b值在初始阶段相对较高,随之降低,弹塑性阶段再次升高,峰值阶段迅速降低,而峰后阶段b值依然相对较高,声发射熵值变化与b值变化恰好相反;随着干湿循环次数的增加,声发射参数的整体量发生明显变化,声发射事件数、能量释放率和熵值均随之降低,而声发射b值随之增加。在不同干湿循环次数作用条件下,弱胶结岩石破坏过程中的声发射多参数变化特征能够反映水对其宏观强度和细观结构物质的劣化作用及影响程度。

Weakly cemented granular rocks(WCGRs)normally have characteristics of low strength,weak cementation,being easily weathered and hydrolyzed.Meanwhile,WCGRs generally contain much moisture.This study focuses on the instability of engineering rock mass affected by dry-wet cycling process.Uniaxial compression tests of WCGRs and AE monitoring technique were adopted to comparatively analyze the deformation and damage characteristics of rock specimens experiencing varying dry-wet cycles.Meanwhile,the change characteristics of number of acoustic emission events(AEEs),energy release rate(ERR),b value and entropy value of AE in the rock damage process were also investigated.Results indicate that:when being subjected to dry-wet cycling process,WCGRs showed apparent deteriorating strength,and the axial strain increases at the peak strength.The number of AEEs and ERR of WCGRs under varying dry-wet cycling effects presented consistent change tendency,i.e.changing slightly in initial stage,gradually increasing when subjected to elastic-plastic deformation stage and reaching the maximum in peak stage.In contrast,the acoustic emission parameter of b value was relatively large in the initial stage,then it decreased before rising in elastic-plastic deformation stage.The b value declined rapidly in the peak stage,but it remained relatively high in post-peak stage.Changes of the AE entropy were opposite to changes of b value.With an increase in times of dry-wet cyclic process,all parameters of AE show following apparent changes:the number of AEEs,ERR and AE entropy all decreased,while the b value increased.Changing characteristics of multiple AE parameters of WCGRs corresponding to varying dry-wet cyclic processes could reveal the degradation influences of water on the rock macroscopic strength and mesoscopic structure matter,as well as the influencing degrees.