次生黄土介质环境地下管线雷达探测正演模拟及实践

FORWARD MODELING AND PRACTICE OF PIPELINE DETECTION IN SECONDARY LOESS ENVIRONMENT

西北地区城镇地下管线大多敷设于自然和人工形成的次生黄土介质环境中,次生黄土介质的介电分布的不均匀性,对探地雷达所探测地下管线反射信号造成的干扰,却往往被工程师忽略,增加了地下管线雷达探测信号解译误差。本文根据西北地区地下管线敷设的次生黄土介质环境特征,基于gprMax建立了非均质和均质土体介质环境中包含金属管及塑料管的介电模型,对上述模型进行了正演。在开展反射信号图像分析、单道反射信号分析和幅度谱分析的基础上,利用工程实践对次生黄土介质环境中敷设的金属管和塑料管探测信号特征进行验证。结果表明:非均质土体介电模型与实际岩土介电模型的图像信号更接近;奇异值法可将实测信号的目标可辨度提升2倍以上;金属管的反射波峰值比塑料管高3.7倍;金属管计算深度比实际深度浅,塑料管计算深度比实际深度深;次生黄土介质环境中,金属管与塑料管的幅度谱的主频应集中在200~400 MHz范围。研究结果可以指导次生黄土环境中金属管和塑料管的信号分析和特征识别,提高探地雷达图像的解译的效率。

Most of the underground pipelines in northwest cities and towns are laid in the natural and artificial formation of secondary loess media environment.When interpreting the radar detection signals of underground pipelines,engineers often overlook the interference caused by the dielectric inhomogeneity of secondary loess on the reflection signals of underground pipelines detected by ground-penetrating radar,thus causing interpretation errors.We established the inhomogeneous and homogeneous soil dielectric models with metal pipeline and plastic pipeline based on gprMax according to the environmental characteristics of secondary loess media for underground pipeline laying in Northwest China,and performed the positive evolution of the above models.On the basis of reflection signal image analysis,single channel reflection signal analysis,and amplitude spectrum analysis,we used engineering practice to verify the signal characteristics of metal pipeline and plastic pipeline laid in secondary loess medium.The results show that:the image signal of the inhomogeneous soil dielectric model is closer to the actual geotechnical dielectric model;the singular value method can improve the target discriminability of the measured signal by more than 2 times;the reflection peak of the metal pipeline is 3.7 times higher than that of the plastic pipeline;the calculated depth of the metal pipeline is shallower than the actual depth,and the calculated depth of the plastic pipeline is deeper than the actual depth;in the secondary loess medium,200~400 MHz is the dominant frequency range of the amplitude spectrum of metal pipeline and plastic pipeline.The research results can guide the signal analysis and feature identification of metal and plastic pipes in the secondary loess environment.