岩石破坏声发射平静期及其分形特征研究

STUDY ON QUIET PERIOD AND ITS FRACTAL CHARACTERISTICS OF ROCK FAILURE ACOUSTIC EMISSION

通过岩石加载的室内试验方法,测试不同岩石破裂全过程的力学特征及其声发射特性,得到岩石破坏全过程力学特性——岩石的全应力-应变曲线、声发射事件累积数、声发射事件率等相关曲线及参数,给出声发射事件数、事件率与应力水平、时间之间的关系。着重讨论一次性加载过程中塑性变形阶段明显的岩石在加载接近峰值强度时单位时间内的应力增长速度减小,也即这一阶段出现明显的"耗时"现象;并且在此阶段监测到的声发射事件率出现明显下降,出现声发射相对平静阶段;而对于塑性变形阶段不明显的岩石来说,这一阶段则基本不存在明显的"耗时"现象,声发射的监测中也没有发现声发射相对平静期现象。另外,还运用分形理论,研究分析处于不同加载应力比的岩样在各个阶段的声发射分形维数,特别是研究声发射平静期维数变化情况。指出在加载初期分形维数处于较低值,且分形维数随加载应力增加而逐步增加;在加载到峰值应力的40%左右时,分形维数开始下降;在加载接近到峰值应力时,即处于声发射平静期阶段时分形维数逐步降到最低,且此时预示着岩石的破坏。此外,结合室内试验,还对现场岩体失稳破坏声发射监测中的一些实际问题进行总结和分析,为更好地应用声发射手段进行岩体稳定性现场监测预报提供理论依据、方法和手段。

Through the load test of rock,different rocks are tested and the mechanical and acoustic emission（AE） characteristics of rocks are studied.Stress-strain curves,AE accumulative total number and AE rate of rock failure are gotten.And AE features including the relationships between AE and time,AE and stress are studied.This study discusses emphatically the AE quiet period of the loading processes to those rocks whose plastic deformation is obvious.In this AE quiet period,the stress increment will be diminished in unit time when stress approaches to peak value strength and it will need more time.Moreover,AE rate will be declined and AE quiet period will also appear in this stage.But for those rocks whose plastic deformation is not obvious,this AE quiet period will not appear.In addition,by fractal theory,the AE values of different stress rates especially at quiet period are calculated and analyzed.It is found that the fractal values are lower in initial loading stages and increase gradually along with stress,about at the 40% of stress rate,fractal values begin to fall down.The fractal values go down to the minimum near the peak value stress and foreshow rock failure.Furthermore,combined with indoor experiment,some problems of in-situ monitoring and prediction are discussed,It gives the theoretical basis and methods for in-situ rock mass monitoring and forecast by AE technology.