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

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

Peer reviewed: YesNRC publication: Ye

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

New leakfinderRT technology: how it works

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

Investigating traffic vibration problems

Aussi disponible en fran\ue7ais: \uc9tude des probl\ue8mes de vibration caus\ue9s par la circulationPeer reviewed: NoNRC 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

A New procedure for evaluating the time domain boundary influence matrix of unbounded media

The finite element method can only deal with finite domains with well defined boundaries. For dynamic problems involving unbounded media, the boundaries of the finite model distort the real physical behaviour of the problem if they remain untreated. For many problems it is possible to formulate so-called silent boundary conditions which perfectly simulate the effect of the truncated unbounded medium. Unfortunately, most of these conditions are properly formulated in the frequency domain. The present paper introduces a new procedure which employs these frequency-dependent boundary conditions to calculate the time domain influence matrix of the truncated unbounded medium. This matrix, which was introduced in a previous publication, is used to calculate the reflection-free response of the truncation boundary one time step ahead of the present time station. The known boundary response is then used as a prescribed condition for the finite model. A one-dimensional example with a frequency-dependent boundary condition si presented to examine the effectiveness of the new procedure. Two other silent boundary conditions formulated directly in the time domain are also examined.La m\ue9thode des \ue9l\ue9ments finis ne peut s'appliquer qu'aux domaines finis comportant des limites bien d\ue9finies. Dans le cas des probl\ue8mes dynamiques mettant en cause des milieux non born\ue9s, les limites du mod\ue8le fini, si elles restent non trait\ue9es, donnent une fausse id\ue9e du comportement physique r\ue9el du probl\ue8me. Pour bien des probl\ue8mes, il est possible de formuler les conditions de limites dites muettes, qui reproduisent parfaitement l'effet du milieu non born\ue9 tronqu\ue9. Malheureusement, la plupart de ces conditions sont formul\ue9es correctement dans le domaine fr\ue9quentiel. Ce document fait \ue9tat d'une nouvelle proc\ue9dure qui permet d'utiliser ces conditions de limites d\ue9pendant de la fr\ue9quence pour calculer la matrice d'influence, dans le domaine temporel, du milieu non born\ue9 tronqu\ue9. Cette matrice, qui a \ue9t\ue9 d\ue9crite dans un document publi\ue9 plus tt, sert \ue0 calculer la r\ue9ponse sans r\ue9flexion de la limite de troncation une phase de temps avant la position pr\ue9sente dans le temps. La r\ue9ponse connue de la limite sert alors de condition prescrite pour le mod\ue8le fini. Afin de d\ue9terminer l'efficacit\ue9 de la nouvelle proc\ue9dure, l'auteur pr\ue9sente un exemple unidimensionnel comportant une condition de limite d\ue9pendant de la fr\ue9quence. Il examine aussi deux autres conditions de limites muettes formul\ue9es directement dans le domaine temporel.Peer reviewed: YesNRC publication: Ye