Research on probing and predicting the diameter of an underground pipeline by GPR during an operation period

• A new method for interpreting the diameter of underground pipeline by GPR.
• This paper verify the reliability of this method by model test and actual project.
• Those factors about the accurate of this method are analysed by FDTD method.

It is very important that the existing networks of underground pipelines be clearly surveyed when the underground space of an old urban area is rebuilt and expanded. The GPR method is always used to locate the embedded pipes; however, it is hard to determine their diameters, especially, when the underground pipe is full of a lossy medium (i.e., water, oil, or gas) during the operation period. First, this paper proposes a new method for probing and predicting the diameter of underground pipelines filled with lossy media based on GPR using the shape of a certain circle determined by the coordinates of three points on this circle. The operational procedure of this method is listed in detail. Secondly, this method is used to detect the diameters of underground pipelines in a model experiment and the project for the detection of a sewage pipe network in Yi’xing chemical industrial park. The measurement value is approximately consistent with the real value. Lastly, some factors influencing the accuracy of this method were comprehensively analysed by applying the finite difference time domain method (FDTD). These factors are the buried depth of the pipe, the detecting frequency of the GPR, the material of the pipe and the spacing of the measured points. The results showed that the proposed method has sufficient applicability and accuracy for practical engineering. These works demonstrate that the proposed method achieves good result.