探地雷达探测围堰抛石层厚的正演模拟与工程应用

Forward modeling and engineering application of ground penetrating radar in detecting riprap layer thickness of cofferdam

基于有限时域差分法,对空气-抛石-土层3层介质进行探地雷达正演模拟,分析雷达波传播过程和典型接收图谱。结果表明,雷达波在介质中以球面波形式传播,能量随传播距离逐渐分散,遇到电学属性不同的界面将产生反射和透射;根据雷达波反射和同相轴连续特征可推测抛石层与土层交界面,根据波形反射异常、波形反向、波速变慢可圈定疑似夹泥等软弱异常区,但多次回波使接收图谱畸变,易引起误判。将探地雷达应用于实际抛石围堰工程探测并结合钻孔勘测,探明了抛石层厚分布和抛石体内异常。

We carry out the ground penetrating radar forward modeling for three layers of air,cofferdam and silt on the basis of finite difference time domain,and analyze the radar wave propagation process and typical receiving patterns.The results show that the radar wave propagates in the form of spherical wave in the medium,and the energy disperses gradually with the propagation distance.When it encounters the interface with different electrical properties,reflection and transmission will be generated.The interface between the riprap layer and the soil layer can be inferred according to the radar reflection and the continuous characteristics of the in-phase axis,and the weak abnormal areas such as suspected mud impregnation can be delimited according to the abnormal reflection of the waveform,reversal waveform and the slow wave velocity.However,the receiving graph is distorted by multiple echoes,which is easy to cause misjudgment.By applying the ground penetrating radar to the actual riprap cofferdam project and combining with the borehole survey,the distribution of riprap layer thickness and the anomaly in riprap body are found out.