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12 May 1995 Remote infrared thermal sensing of sewer voids
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Many sewers in America's cities are more than 125 years old and are subject to structural failure. In one year alone, St. Louis, Missouri had 4,000 sewer collapses that carried an astronomical repair tag. When a sewer caves in, it often takes the street, sidewalks, and surrounding buildings along with it endangering public health and safety. The ideal situation would be to repair a sewer before such cave-ins occur, as emergency repairs are far more costly than preventive measures. The question addressed by this paper is how to detect unseen problem areas in sewer systems before collapses occur. At the present, progressive sewer administrations may use crawl crews or remote controlled video cameras to inspect sewers at suspected problem locations. This can be extremely costly, dangerous, and not very accurate, as a void around the outside of the sewer is often invisible from within. Thus, even a crawl crew can fail to detect most voids. Sewer districts and independent engineering firms have found infrared thermography, a nondestructive testing method, to be extremely accurate in finding sewer voids, and accompanying pipeline leaks, before they can cause expensive and dangerous problems. Infrared thermography is a non-contact, remote sensing method, with the potential for surveying large areas quickly and efficiently.
© (1995) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Gary J. Weil "Remote infrared thermal sensing of sewer voids", Proc. SPIE 2454, Nondestructive Evaluation of Aging Utilities, (12 May 1995);

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