Abstract Summary
Leakage in buried pipes is the main source of wastage in water distribution systems. The issue of promptly pinpointing and fixing the leaks is thus of great interest to minimize water wastage. One way to pinpoint a leakage is to measure two acoustic signals, on the pipe, one each side of the leak and estimate its position from the delay of arrival between the signals, given the velocity of the fluid-borne wave that propagates from the leak along the pipe. This technique is limited by the necessity of access points to the buried pipe, by the distance from the leak and measurement points and a good estimate of the velocity of the fluid-borne wave. Moreover, it is necessary to have some a priori knowledge of the probable location of the leak before taking the measurements. To complement this approach, we propose an alternative technique based on surface vibration measurements in an area above the leak. The technique involves a “seismic camera”, which measures the acoustic signal generated by the leak on the ground surface with an array of geophones and analyses the data using steering vector array algorithms. Although the proposed concept may appear to be similar to existing acoustic cameras, it differs drastically. Acoustic cameras are developed based on the acoustic wave propagation in fluids in which only longitudinal pressure waves propagate at the local sound velocity. In soil two or more different wave-types may propagate with different phase velocities. Also, the pressure oscillation caused by waves in a fluid is an omnidirectional scalar quantity, whereas the velocity oscillation of particles in a solid is vectorial. In this paper, the concept of the seismic camera is described, then the effects of multiple wave types and the measurement direction are investigated numerically. A simulation of a monopole source inside an infinite thin cylindrical shell in an unbounded media is performed to assess the array signal filtering performance. Results from the numerical simulation show that a specific wave type (shear or longitudinal) dominates the vibration response depending on the frequencies radiated by the leak. These observations are also investigated experimentally with measurement of vibration radiated by a buried pipe excited by an open valve to simulate the leak. The results show that the use of array signal processing in vibration measurements around the leakage may be a useful addition to existing techniques in the location of leaks in buried water pipes.
