In-Pipe Stress-Wave-Based Detection of Voids Behind Concrete Sewer Pipes

To identify voids around underground concrete sewer pipes, we investigate an automated in-pipe detection method. This method uses a robotic platform with a mechanical impactor to generate non-destructive stress waves at any angular position on the pipe's inner circumference. The resulting acoustic waves are recorded with a microphone and are analyzed to make a void location map around the pipe. To characterize the method, we developed numerical models where we examine the influence of void width, height, and shape, and the thickness of the pipe and the presence of reinforcement in the pipe on the void detection. We validated the proposed method by conducting experiments inside a concrete pipe with custom-made voids, and differently compacted areas in the pipe’s surrounding. The results showed that the method was able to detect voids and areas with less compacted sand around the pipe.