Experimental Investigation into the Influence of Backfill Types on the Vibro-acoustic Characteristics of Leaks in MDPE Pipe

Pipe leak location estimates are commonly conducted using Vibro-Acoustic Emission (VAE) based methods, usually using accelerometers or hydrophones. Successful estimation of a leak's location is dependent on a number of factors, including the speed of sound, resonance, backfill, reflections from other sources, leak shape and size. However, despite some investigation into some of the aforementioned factors, the influence of backfill type on a leak's VAE signal has still not been experimentally quantified. A limited number of studies have attempted to quantify the effects of backfill. However, all of these studies couple other variables which could be equally responsible for their observed changes in leak signal. There have been no controlled studies where one variable can be directly compared to one another (i.e. all variables remain constant, only changing backfill type). The aim of this paper is to better characterise the influence of backfill on a leak's VAE signal by individually isolating all variables. For the first time, this paper demonstrates the influence of backfill on leak VAE signal by keeping all other variables consistent. It was found that the backfill type had a strong influence on the frequency and amplitude of leak signals, which is likely to have a significant impact on the accuracy of leak location estimates

Wavenumber prediction and measurement of axisymmetric waves in buried fluid-filled pipes: Inclusion of shear coupling at a lubricated pipe/soil interface

Acoustic methods have been widely used to detect water leaks in buried fluid-filled pipes, and these technologies also have the potential to locate buried pipes and cables. Relatively predictable for metal pipes, there is considerably more uncertainty with plastic pipes, as the wave propagation behaviour becomes highly coupled between the pipe wall, the contained fluid and surrounding medium. Based on the fully three-dimensional effect of the surrounding soil, pipe equations for n=0 axisymmetric wave motion are derived for a buried, fluid-filled pipe. The characteristics of propagation and attenuation are analysed for two n=0 waves, the s=1 wave and s=2 wave, which correspond to a predominantly fluid-borne wave and a compressional wave predominantly in the shell, respectively. At the pipe/soil interface, two extreme cases may be considered in order to investigate the effects of shear coupling: the “slip” condition representing lubricated contact; and the “no slip” condition representing compact contact. Here, the “slip” case is considered, for which, at low frequencies, analytical expressions can be derived for the two wavenumbers, corresponding to the s=1 and s=2 waves. These are both then compared with the situations in which there is no surrounding soil and in which the pipe is surrounded by fluid only, which cannot support shear. It is found that the predominant effect of shear at the pipe/soil interface is to add stiffness along with damping due to radiation. For the fluid-dominated wave, this causes the wavespeed to increase and increases the wave attenuation. For the shell-dominated wave there is little effect on the wavespeed but a marked increase in wave attenuation. Comparison with experimental measurements confirms the theoretical finding

Difficulties with phase spectrum unwrapping in spectral analysis of surface waves nondestructive testing of pavements

This paper presents the results of a case study for near-surface profiling of a pavement site using the SASW method. In this study, inconsistencies were observed in the dispersion curve of the site when the usual procedure of unfolding the relative phase spectrum was followed. A correction procedure to eliminate these inconsistencies is suggested and discussed. The thickness and wave velocities of the various layers obtained with the SASW method, after applying the correction procedure, matched closely those determined from cored samples and crosshole tests.Ce document pr\ue9sente les r\ue9sultats d?une \ue9tude de cas relativement au profilage subaffleurant d?un site de rev\ueatement, selon la m\ue9thode de l?analyse spectrale des ondes de surface (SASW). Dans le cadre de cette \ue9tude, on a not\ue9 des discordances dans la courbe de dispersion du site lorsque la marche \ue0 suivre habituelle consistant \ue0 mettre en relief le spectre de phase relative a \ue9t\ue9 observ\ue9e. Une proc\ue9dure de correction permettant d?\ue9liminer ces discordances est ici sugg\ue9r\ue9e et examin\ue9e. L?\ue9paisseur ainsi que les valeurs de c\ue9l\ue9rit\ue9 des vagues des diverses couches obtenues avec la m\ue9thode SASW, une fois appliqu\ue9e la proc\ue9dure de correction, ont concord\ue9 de pr\ue8s avec celles d\ue9termin\ue9es \ue0 partir d?\ue9chantillons carott\ue9s et d?essais \ue0 per\ue7ages transversaux.Peer reviewed: YesNRC publication: Ye

Nondestructive evaluation of pavements using spectral analysis of surface waves in the frequency wave-number domain

Peer reviewed: YesNRC publication: Ye

Evaluation of human response to building vibration caused by transit buses

This paper demonstrates the application of these standards for the case of vibrations induced in residential homes by transit buses. Difficulties and ambiguities in applying the standards are revealed. Several vibration evaluation methods were applied and compared including rms, rmq, peak, and vibration-dose-value methods. Actual vibration levels measured in 6 residential homes were used to assess the various methods. Two evaluation methods were identified as the most appropriate.Nous d\ue9montrons dans ce document l?application de ces normes relativement aux vibrations produites dans les b\ue2timents d?habitation par les autobus urbains. Des difficult\ue9s et des ambigu\ueft\ue9s concernant l?application des normes sont ici mises au jour. Plusieurs m\ue9thodes d?\ue9valuation des vibrations ont \ue9t\ue9 mises en ?uvre et compar\ue9es, dont les suivantes : valeur efficace; valeur quadratique moyenne; valeur de cr\ueate; et valeur de la dose de vibrations. On a utilis\ue9 les niveaux de vibration r\ue9els ayant \ue9t\ue9 mesur\ue9s dans six (6) b\ue2timents d?habitation aux fins de l?\ue9valuation des diverses m\ue9thodes retenues. Deux (2) des m\ue9thodes d?\ue9valuation ont pu \ueatre identifi\ue9es comme \ue9tant les plus appropri\ue9es \ue0 cette fin.Peer reviewed: YesNRC publication: Ye

Researchers advance non-destructive method for testing of pavements using genetic algorithms

Aussi disponible en fran\ue7ais: Am\ue9lioration d'une m\ue9 thode d'essais non destructifs pour chauss\ue9es utilisant les algorithmes g\ue9n\ue9tiquesPeer reviewed: NoNRC publication: Ye

New leakfinderRT technology: how it works

Aussi disponible en fran\ue7ais: La technologie LeakfinderRT: mode d'emploiPeer reviewed: NoNRC publication: Ye

Analysis of wave propagation in unbounded media

A new procedure is presented to account for the radiation condition of unbounded media analysed using the finite- element method in the time domain. The medium is divided into a finite region that is of interest in the analysis, and the remaining unbounded medium. The stiffness contribution of the latter is properly represented by its boundary influence matrix, which is directly calculated in the time domain. This procedure is suited for situations in which many analyses of the finite region must be performed.Une nouvelle aproche est propos\ue9e pour tenir compte de l'aspect "infinit\ue9" des milieux non born\ue9s analys\ue9s au moyen de la m\ue9thode des \ue9l\ue9ments finis dans le domaine temps. Le mileu est divis\ue9 en une r\ue9gion finie, qui pr\ue9sente un int\ue9r\ueat dans l'analyse, et un milieu r\ue9siduel non born\ue9. L'apport en rigidit\ue9 de ce dernier est bien repr\ue9sent\ue9 par la matrice d'influence de sa limite avec la r\ue9gion finie; la matrice est calcul\ue9e directement dans le domaine temporel. Cette approche convient aux situations o\uf9 il faut effectuer de nombreuses analyses de la r\ue9gion finie.Peer reviewed: YesNRC publication: Ye