Modelling of ground penetrating radar backscatter for water pipeline leakage detection

Abstract

Subsurface water leaks not only waste precious natural resources, but also create substantial damages to the transportation system and structures within urban and suburban environments. While many geophysical techniques have been suggested for detecting water leakage including ground-penetrating radar (GPR), acoustic devices, gas sampling devices and pressure wave detectors, there is no ideal solution for it. Nonetheless, GPR, a non-destructive geophysical technique which uses high frequency electromagnetic waves to acquire subsurface information has been regularly utilized as GPR responds to the changes in electrical properties, which is a function of soil and rock material, and moisture content. To evaluate the feasibility of GPR in detecting water pipe leakage, a finite-difference time-domain (FDTD) numerical modelling is conducted together with water pipe leakage detection fieldwork and experimental test. To properly design the features of the imaging approach, and test its capabilities in controlled conditions, the synthetic data was generated in a two dimensional FDTD forward modelling solver capable of accurately simulating real world GPR scenarios. Different types of simulate conditions involving sizes of leakage area, frequencies (250 MHz and 700 MHz), pipe materials (AC, DI, PVC, MS and HDPE) and pipe sizes (100mm, 200mm and 300mm) were conducted. For the fieldwork, case studies were carried out using GPR scanning equipment (Detector Duo) to validate FDTD numerical model. For the experimental test, Detector Duo was used to collect data on top of District Metering Areas testbed. More understanding regarding the signature of leakage was gained in radargram. Compared to a distinct hyperbola or line as shown in radargram of intact pipes, the leakage zone is disturbed by the wave reflection caused by saturated soil. Numerically simulated results seem to be in agreement with the case studies and experimental results. The signature of pipe and leakage are clearly visible in the simulated radargram compared with those in the case studies and experimental radargram. Therefore, GPR survey seems promising as an efficient non-destructive geophysical technique for leakage detection approach. This finding is useful to provide protocols for GPR profile interpretation, particularly in underground water pipe leakage detection.