Acoustic Wave Attenuation through Buried Water Mains

Abu Hena Muntakim, Ashutosh Sutra Dhar, Amgad Hussein

In the proceedings of: GeoOttawa 2017: 70th Canadian Geotechnical Conference; 12th joint with IAH-CNC

Session: Transportation Geotechnics III - Roads B

ABSTRACT: This paper describes a laboratory facility developed at Memorial University of Newfoundland for the study of acoustic wave propagation from leak noise through buried pipes and the results of acoustic emission testing in the new laboratory facility. The facility is designed and developed to investigate the propagation of leak noise through water mains. The developed test facility is used to investigate leak noise attenuation through an in-air and a buried pipe. The buried pipe is backfilled with crushed stone. The laboratory study indicates that the leak noise attenuates during propagation of acoustic wave. The attenuation is higher for the high frequency waves. The attenuation also increases with the increase of flow rate through the pipe. Between the in-air pipe and the pipe buried in crushed stone, the attenuation is higher for the buried pipe. For a distance of 0.6 m, the amplitude ratio (the ratio of the amplitude at two locations at a distance of 0.6 m and 1.2 m from the source, A0/A1) is 0.987 for in-air pipe and 0.93 for pipe buried in crushed stone at a frequency of 2000 Hz and an inflow rate of 6.7 gallons per minute (25.36 litres per minute). An attenuation parameter is calculated based on the amplitude ratio to be 0.032 dB/m for in-air pipe and 0.12 dB/m for the buried pipe. Using the experimental results, a finite element modelling technique is developed for simulating the acoustic wave propagation and determining the effective distance of sensor from the leak source for successful identification of the leak noise. RÉSUMÉ. - dans les nutilisée pour étudier lle tuyaux tuyaux enfoui dans la pierre concassée à une fréquence de 2 000 Hz et un 0,12 dB/m pour le tuyaux enfouis. À partir des résultats expérimentaux, une technique de modélisation par éléments finis a été développé pour simuler la propagation des ondes acoustiques et déterminer la distance effective du capteur de la source de la fuite pour une identification réussie du bruit de fuite. INTRODUCTION 1. Acoustic is often used for inspecting, testing, evaluating material and elements for discontinuities in continuum. Acoustic emission method is one of the popular methods used for detecting leak in water mains. In this technique, acoustic noise from leak is propagated through pipe that is received at two access points to the pipe. Successful leak detection using this method depends on the propagation characteristics of the acoustic noise. Noise can be attenuated while propagating through the pipeline. Thus, if the sensors are not located close enough, the leaks may remain undetected. Understanding the propagation behaviour of acoustic wave is therefore very important for determining the distance over which the method would be successful. In order to develop a better understanding of the wave propagation through buried pipe, an experimental investigation under controlled conditions is required. A full scale pipe test would be ideal for the experimental investigation. Full-scale experiments are however complex and expensive. Literature on full-scale testing on acoustic wave propagation is therefore limited. Juliano et al. (2013) tested a 304.8 m long buried steel water pipe for leak detection using acoustic emission technique. They used a 305 mm diameter, welded steel pipeline. Vertical access tubes were used to gain access to 17 different locations along the pipe. In their tests, a range of leak rates from 15.2 mL/s to 16.6 mL/s was successfully detected when the maximum sensor distance was 65.5 m. However, for a sensor distance of 78 m or above, the acoustic emission method was not successful, potentially due to the attenuation of the sound wave. The attenuation characteristics were however not investigated. Pollock and Hsu (1982), Lee and Lee (2006) and Thenikl et al. (2012) studied attenuation characteristics of acoustic wave propagation during leak detection using amplitude ratio. In the method of Thenikl et al. (2012), noise is recorded at two different locations along the length of the pipe and ratio of the averaged amplitude was taken to determine the exponential law of attenuation. The attenuation characteristic is given by Equation 1.

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