利用地质雷达GPR(Ground Penetrating Radar)正演程序研究隧道环境下的地质情况,可以为隧道超前预报提供解释依据,提高解释精度,避免安全事故的发生。通过从理论上的正演数值模拟计算,成果表明:采用50 MHz的低频天线,地质雷达的有效预报距离在30 m左右;地质雷达在识别破碎带、溶洞等地质体顶界面的埋深和形状上比较准确,反射波同相轴与理论模型基本吻合;单道数据的波相位变化、振幅大小变化可以提供隧道前方围岩介电常数的变化趋势;复杂模型下电磁波衰减相对更迅速,模拟效果要弱于单一的地质模型。通过2段应用实例,验证了正演模拟部分的论证,为解释同等形状的反射波特征提供了参考依据。
Abstract
Forecasting tunnel’s geological conditions using forward procedures of GPR (ground penetrating radar) provides interpretation basis, improves the accuracy of interpretation and helps avoid accidents. Currently most forward modellings are focused on the tunnel lining, but less on the surrounding rock in front of the working face.Through theoretical forward simulation by establishing large-scale geological model together with low-frequency antenna, we conclude that 1) the effective forecast distance is about 30m by using low-frequency antenna of 50MHz; 2) GPR could accurately identify the depth and shape of fracture zone, caves and other geological bodies, and cophase axis of reflected waves is consistent with that in theoretical model; 3) the variation trend of dielectric constant of surrounding rock in the front could be obtained from the wave phase and amplitude changes of single-channel data; 4) the electromagnetic waves attenuate more rapidly in complex model, and the simulation result is weaker than that of single geological model. Finally, we give two application examples to verify the forward modelling and provide a reference for reflected waves with the same shape.
关键词
隧道工程 /
超前预报 /
GPR /
有限差分 /
正演模拟
Key words
tunnelling engineering /
advance forecast /
GPR /
finite difference /
forward simulation
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