On the role of vibro-acoustics in leak detection for plastic water distribution pipes

Leaks have been detected and localized in water distribution in many countries for years, by using the cross-correlation of pipe vibration measured either side of a suspected leak and/or by using listening sticks. However, in modern plastic pipes this is problematic because of the strong coupling between the water and the pipe which results in significant attenuation of the coupled fluid-pipe wave, which in turn is responsible for the propagation of leak noise. Hence leak noise does not propagate as far as it did in older metallic pipes. This paper discusses how the vibro-acoustic behavior of the water-pipe-soil system influences leak noise propagation. To investigate this, a numerical model is developed, and the results are compared with those from an analytical model for two water pipe systems, one in the UK and one in Brazil. Experimental results are also presented. It is shown that the important difference between the two systems is the shear stiffness of the surrounding soil, which has a profound effect on both the speed of leak noise propagation and the attenuation of the noise along the pipe