基于RA与AF值的声发射指标在隧道监测中的可行性

Feasibility research of AE monitoring index in tunnel based on RA and AF

基于华蓥山隧道掘进爆破过程中的声发射监测结果,对比了上升时间/振幅比值(RA)与平均频率(AF)在不同传播距离下的分布规律,结果表明,随传感器与震源间距离增加,RA最大值增加,AF的分布范围基本不变.为验证基于RA与AF值描述岩体破裂情况的有效性,研究了RA/AF比值r在破裂过程中的变化规律以及r的变异系数的发展规律,并与常用的参数指标绝对能量、b值等参数进行对比验证.本文提出了3种变异系数(CV)计算方法,对比计算结果并探讨了各方法的适用条件.由计算结果可知,r值变异系数能够较好地描述岩体中的破裂发展过程,其中CV1计算方法适用于声发射信号较离散的情况,而CV3的计算方法更适用于存在连续声发射信号的围岩监测.

Risetime/amplitude(RA)and average frequency(AF)have been usually used for qualitative analysis of fracture mechanism in acoustic emission(AE)monitoring.However,regardless whether fracture is shear or tensile in macroscopic view,it can be observed in laboratory experiments that the AE signals of shear increases when it is close to the failure stage of specimens.Therefore,RA and AF may also have the potential in indicating the violent reputure of rock.Furthermore,as the value of RA would increase with the distance within some limits,the observed RA and AF would be closer to the shear feature,which means the index is relatively safer under attenuation and is appropriate for in-situ monitoring.Based on the data monitoring of Huayingshan Tunnel,Yuguang Expressway during the construction process,the distributions of RA and AF on positions of different distances of the seismic source were compared.Results show that the maximum value of RA increases distinctly with the distance increase between the sensors and the seismic source,whereas the distribution of values of AF are nearly the same at different distances.To verify the validity of RA and AF in indicating the rupture of rock,parameter r of RA/AF ratio was set and the time history of r and coefficient of variation(CV)of r during the rupture process were studied and compared with other regular indexes,such as absolute energy and b value.The variation of CV could describe the intense rupture of rock properly and the analysis of CV could get a safer evaluation result especially when dealing with small-scale failure in rock mass.To find the best statistical method of CV,three statistical methods of CV were compared and results show that the CV of r can well illustrate the rock rupture,CV1 is more suitable for situations that the AE signals vary and are discrete,and CV3 is appropriate for monitoring of continuous AE signals.