探地雷达检测隧道衬砌渗漏水方法研究

A Tunnel Lining Leakage Detection Method Using Ground Penetrating Radar

渗漏水是危害隧道安全的常见病害之一,针对衬砌表面有装饰层遮挡的隧道,提出了在装饰层外检测渗漏水的探地雷达方法。首先,根据对电磁波传播特性进行分析,从理论上论证了该方法的可行性,得出衬砌有无渗透水时其表面电磁波反射系数不同。当衬砌表面的反射系数小于-0.433时,可认为该处有渗漏水发生。然后,给出了从雷达回波中判定渗漏水的方法,通过试验探测获得衬砌无渗漏条件下的探地雷达回波作为参考信号,将检测得到的雷达回波与已知无渗漏水条件下的雷达回波做差,有渗漏水时在衬砌表面会出现负向反射,且渗漏量越大反射越强烈。最后,通过数值模拟试验对所提出的方法进行验证,采用电磁波时域有限差分法模拟探地雷达在隧道装饰层外对衬砌进行探测,分别模拟衬砌无渗漏有渗漏情况下的探地雷达回波。将模拟的回波减去衬砌无渗漏条件下的回波后,从振幅分析可以得出:衬砌无渗漏发生时,振幅保持为零,在有渗漏水位置负向振幅显著增大,且渗漏水越严重的位置反射越强;该方法能有效检测出衬砌出现渗漏的部位,且通过对回波的振幅分析可定性评价渗漏量的大小。所提方法有效易行,在实际工程中具有一定的应用推广价值。

Leakage is a common disease jeopardizing the safety of tunnels. Aiming at the tunnels covered by decorative layers on the lining surface, a novel method for detecting lining leakage from outside the decorating layer using GPR is proposed. First, according to the analysis of electromagnetic wave propagation, the proposed method is proved feasible from electromagnetic theory. The value of reflection coefficient from leaky lining is different from that of dry one. When the reflection coefficient of the lining surface is less than-0.433,it can be considered that there is water leakage there. Then, the leakage identification method from GPR echo is provided. The GPR echo under the condition of no leakage of lining is obtained as a reference signal through experimental detection. To subtract the known GPR signals of drying lining from the obtained ones, the result will be the indicator. Negative reflections from lining surface represent leakage of lining, and the larger the leakage, the stronger the reflection. Finally, the proposed method is verified by numerical simulation. The GPR detection of a tunnel lining from outside the decorating layer is simulated by using finite-different time-domain method, and the GPR echos of lining with and without water leakage are simulated respectively. After subtracting the echo without water leakage from the simulated echos, it can be seen from amplitude analysis that(1) the amplitude remains zero when no leakage occurs, while the negative amplitude increases significantly at leakage locations, and the reflection is stronger when the leakage is more severe;(2) this detection method can find the location of leaky areas effectively, and leakage amount can be evaluated qualitatively from amplitude analysis of echos;The proposed method is efficient and convenient, it has certain application and promotion value in practical engineering.