Detecting underground water leak from the pipelines by radar and infrared techniques

Water leaks in urban underground pipelines not only cause economic losses but also result in structural damage to roads and buildings. Currently, there are several methods for detecting water leaks, such as pressure/flow sensors or fiber optics, but they require sensors to be installed in advance. Acoustic methods are effective for detecting leaks in metal pipes, but they are less effective for plastic pipes. Considering that in France, around 45% of drinking water pipes are made of plastic, we need methods that are user-friendly, sufficiently accurate, and that can work for all types of pipes. Therefore, the application of radar and thermal infrared (TIR) camera can be alternatives. Radar detection operates on the principle of dielectric contrast between dry and wet soils, whereas TIR relies on their temperature difference. Considering the complex constituents in unsaturated soils, in this study, firstly to understand the material’s effects on radar signals propagation, we discussed the relations between dielectric properties and water saturations in three types of soils. Secondly, we prepared a laboratory-scaled model (80*60*50 cm) to observer water leaks process in three soils. A stepped-frequency radar and an IR camera were employed to monitor the changes in signals and TIR images resulting from water drainage and potential soil deconsolidation due to liquefaction. Finally, we built a full-sized site to detect the water leak under the depth of 1m by ground penetrating radar. Based on these experimental results, we hope to propose a way to summarize an optimal nondestructive methodology for on-site detecting.