单轴多级加载岩石破坏声发射特性试验研究

在单轴多级加载条件下，进行花岗岩破坏全过程的声发射试验研究，得到应力-应变、声发射参数与应力和时间的关系。研究结果表明：每级荷载稳压时AE事件率、能率降低，而AE事件数基本稳定或增加平缓，表明稳压阶段试样内原有裂纹未发展、新生裂纹少、声发射水平低。随时间的延长和轴向荷载的增加，AE事件率增加，表明试样内裂纹逐渐增多或其内在裂隙逐步贯通。室内单轴多级加载试验在一定程度上反映出地下厂房分级开挖时应力调整前后声发射的趋势变化，建议在高地应力区进行水电地下厂房岩爆等地质灾害的现场声发射监测时，应选取合适的监测时机，特别要在上下台阶贯通时加强监测。整个加载过程中存在初始区、剧烈区和下降区，多数试样临近峰值强度时声发射活动活跃，尔后AE事件数趋于平缓，AE事件率下降，出现声发射平静期现象。与其他学者的室内和现场试验研究成果作一对比，认为岩体破坏发生前多出现声发射的突然下降或相对平静期现象，并在物理过程上对此作一探讨，为现场岩体稳定性监测与预报的判据提供借鉴和思路。

EXPERIMENTAL STUDY ON ACOUSTIC EMISSION CHARACTERISTICS OF ROCK FAILURE UNDER UNIAXIAL MULTILEVEL LOADINGS

Experiments on acoustic emission(AE)characteristics of complete granite failure process are carried out under uniaxial multilevel loadings.Relations between stress and strain,and relations of time with AE characteristics and stresses are obtained.The results show that during load stability period,AE rate and AE energy decrease,but AE events remain constant approximately,which show that cracks are not developed and AE level is low.During load increase period,AE rate raises,indicating that cracks are developed.The uniaxial multilevel loading experiments reflect AE trend during stress regulation to certain degree when underground powerhouse is excavated step by step.It is suggested that,for rockburst geologic hazards,appropriate monitoring opportunity should be adopted during AE monitoring,especially AE monitoring should be strengthened when the upper and nether steps are joined.AE progress of rock failure includes initial phase,tempestuous phase and drop phase.When the curve reaches to its peak phase,major AE of events rock samples are active.Then AE events remain constant approximately and AE rate drop,indicating that there is a relatively quiet period.Compared with experimental studies of other scholars both in laboratory and in field,it is considered that relatively quiet period of AE appears before rock failure,and then,the phenomenon is discussed with physical mechanism.The relatively quiet period of AE before rock failure can provide reference to rock mass stability monitoring and prediction.