隧道衬砌空洞敲击回声特性

Knocking Echo Characteristics of Tunnel Lining Cavity

为提高隧道衬砌空洞检测效率、指导隧道衬砌空洞自动敲击检测装置研制,开展隧道衬砌空洞敲击回声特性研究。依托我国双线隧道结构形式建立隧道衬砌声-结构耦合模型,以边长分别为0.4,0.6和1.0 m、衬砌厚度分别为0.05,0.15和0.35 m的9种空洞为重点,仿真分析敲击力、敲击点位置、空洞边长和衬砌厚度与衬砌回声声场分布特性间的关系;通过模型试验,验证仿真模型参数设置及仿真分析方法的可靠性。结果表明:空洞边长越大或空洞处衬砌厚度越小,基频越低;9种空洞的振动主频在318~1 837 Hz,计算时按200~2 000 Hz取值,该范围下隧道空间内声模态对隧道衬砌敲击回声声场分布影响较小;为识别边长0.4 m、衬砌厚度0.15 m的最小空洞,敲击力幅值应不小于5 kN,脉冲宽度应不大于0.3 ms;回声采集传感器应布设在距敲击点不大于1.0 m,且与敲击点轴线夹角不大于30°的范围内;面积不小于1.0 m^(2)、衬砌厚度小于0.20 m的空洞,其敲击回声声压级超过50 dB,空洞特征易于识别。

In order to improve the detection efficiency of tunnel lining cavity and guide the development of the automatic knocking detection device for tunnel lining cavity,the study on the knocking echo characteristics of tunnel lining cavity was conducted.Relying on the structural form of double-track tunnels in China,an acousticstructural coupling model of tunnel lining was established;regarding 9 kinds of cavities with side lengths of 0.4,0.6 and 1.0 m,and lining thicknesses of 0.05,0.15 and 0.35 m respectively as key points,the relationship between the acoustic field distribution characteristics of the lining echoes and the impact force,impact position,cavity side length,as well as the lining thickness was simulated and analyzed.The reliability of the parameter settings for simulation model and simulation analysis methods was verified through model experiments.The results show that the larger the side length of the cavity or the smaller the lining thickness at the cavity,the lower the fundamental frequency.The main frequency range of vibration of the 9 kinds of cavities is 318-1,837 Hz,and the range is fixed as 200-2,000 Hz in the calculation,under which the acoustic modes in tunnel space have little influence on the acoustic field distribution of tunnel lining knocking echo.In order to identify the smallest cavity with a side length of 0.4 m and a lining thickness of 0.15 m,the amplitude of the knocking force should be no less than 5 kN,and the pulse width should be no more than 0.3 ms;the echo acquisition sensor should be located within a distance no more than 1.0 m away from the knocking point,and at an angle no greater than 30° with the axis of the knocking point.For cavity with an area no less than 1.0 m^(2) and a lining thickness less than 0.20 m,the sound pressure level of its knocking echo exceeds 50 dB,and the characteristics of the cavity are easy to be identified.