Canadian Consulting Engineer

INFRASTRUCTURE: Maintenance Issues

The maintenance of Canada's urban infrastructure systems requires huge financial commitments from municipalities and provincial governments. They must make tough decisions every day regarding products...

January 1, 2002  By Robert Bullis for Institute for Research in Construction, Nation

The maintenance of Canada’s urban infrastructure systems requires huge financial commitments from municipalities and provincial governments. They must make tough decisions every day regarding products, services, materials, equipment and practices, and they and their consulting engineers are constantly searching for better ways of doing things.

Fortunately, the National Research Council’s Institute for Research in Construction (IRC) has a number of co-operative projects giving insights into the causes of infrastructure problems. The research is being carried out in IRC’s Urban Infrastructure Rehabilitation Program. IRC also offers tools to help clients develop cost-effective solutions.

On the surface — dealing with utility cuts

Surveys show that pavement restoration following underground work on utilities is a major challenge facing municipalities and utility providers, with huge cost implications for both.

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IRC researcher Dr. El Hussein Mohamed heads a utility cut research project launched by IRC in collaboration with the Cold Regions Research and Engineering Laboratory (CRREL) of the U.S. Army Corps of Engineers and 26 other partners. The partnership list includes cities, state transportation departments and utilities in the U.S. and Canada. The project is in its second year, but new partners are still being invited to join in order to increase the number of experiments carried out.

The project is examining more effective options for reinstating utility cuts, and will develop models to predict how reinstated roads will perform. The models will provide the basis for a best-practice guide and guide to selecting materials. The researchers will also develop a software tool that will predict the performance of a reinstated road and evaluate alternative strategies. The ultimate goal is to arm municipalities and utilities with information enabling them to make informed decisions before issuing permits and sending contractors out to dig up a street.

To date, four field experiments have been constructed as part of the investigation — in Ottawa, Toronto, Chicago and Los Angeles. As well, IRC and CRREL conducted a North America-wide survey of municipalities and utility providers. The survey asked questions about typical road composition, construction procedures and standards, materials and equipment, quality control measures etc. It also touched on management approaches. The results are being analyzed, with the results due May 2003.

For more information, contact Dr. Mohamed at (613) 993-3817, e-mail mohamed.hussein@nrc.ca.

A seal in time —

road maintenance

More than two-thirds of Canadian roads fall under municipal jurisdiction, notes Dr. Jean-Franois Masson, IRC researcher. Of those, 90 per cent are in need of immediate repair. Preventive maintenance is the key to delaying road reconstruction, and sealing cracks as they occur is an increasingly important way to do this. Effective crack sealing can increase pavement service life by 10-20 per cent and save Canadian municipalities more than $800 million over the next 20 years.

“Effective” is the key word. “As easy and common as the technique is, crack sealing is not being used as effectively as it should,” Dr. Masson says. “Sealant failure within three years of application is common, and failures often occur within the first year, usually because of inappropriate selection and installation of materials — a direct result of inadequate performance guidelines.”

IRC reviewed the installation of sealant in its publication, Effective Sealing of Pavement Cracks in Cold Urban Environments. While this guide is now used throughout Canada, it left open the issue of sealant selection. Now, in partnership with the Virginia Tech Transportation Institute, IRC is building a consortium to study that issue.

Over several years, the consortium project will develop procedures to measure the aging effects of bituminous sealants, a method to assess sealant performance, a sealant adhesion test that takes into account aggregate type, and performance guidelines for sealant selection. These guidelines, says Dr. Masson, will help users select sealants based on specific local needs such as climate conditions, thus extending the product’s service life.

To find out more, contact Dr. Masson at (613) 993-2144, e-mail jean-francois.masson@nrc.ca.

Going underground — managing large sewers

The failure of deeply buried large sewer structures (more than 900 mm in diameter) can have enormous consequences, both physically and financially. And maintaining these systems can be equally difficult and expensive. A new IRC publication, Guidelines for Condition Assessment and Rehabilitation of Large Sewers, can help municipalities and their consulting engineers more efficiently manage large sewer assets (both flexible and rigid pipes). The publication was written by the IRC research team of Dr. Jack Zhao, Shelley McDonald and Dr. Yehuda Kleiner.

Like many other IRC research initiatives, says Dr. Zhao, the publication is the product of a collaboration between IRC, government departments and private companies including R.V. Anderson Associates, Toronto; and M.E. Andrews Associates, Ottawa.

The systematic assessment approach goes beyond identifying defects and coding them, to assessing the condition of the structure, its importance to the system, and its rehabilitation requirements. The first step in the process is to compile an inventory database of all pipes and access holes. An impact assessment is then carried out using a rating system that considers factors such as location, type of soil, pipe size, burial depth, sewer function and seismic zone. An evaluation of the results gives an overall impact rating for a pipe segment, and these ratings are placed on a map of the sewer system for easy identification of “hot spots.”

The impact rating allows municipalities to determine the most likely locations for problems, and to prioritize segments for inspection. During the course of the inspections, defects are identified and coded using IRC’s approach to rate their type and severity. The approach recognizes two main types of defect — service or structural — and up to three levels of severity.

The final step is a condition assessment based on the impact, structural and service ratings. This condition assessment provides the basis for decisions about the rehabilitation approach: do it now, do it within the next five years, or leave it alone. Once the decisions have been made about rehabilitation and required inspection frequency, the pipe or access hole is returned to the database until its next scheduled inspection.

To order Guidelines for Condition Assessment and Rehabilitation of Large Sewers, contact 1RC’s Publication Sales office, 1.800-672-7990, (613) 993-2463.

The sound of running water – locating leaky pipes

Clean, safe drinking water is a precious commodity in today’s world, and delivering huge amounts of it with as little waste as possible is critical. Unfortunately, in most water distribution systems, a large amount of water — 20-30 per cent in typical systems, and as high as 50 per cent in older ones — is lost in transit between treatment facilities and consumers. The major cause of these losses is usually leakage.

Water utilities primarily use acoustic devices to locate leaks, but Dr. Osama Hunaidi, IRC researcher, points out that these devices have limitations, particularly in the detection of leaks in plastic pipes (increasingly used in water distribution systems), large-diameter concrete pipes, or pipes in clay soils or below the water table.

In 1998, IRC researchers participated in a project funded by the American Water Works Association Research Foundation to investigate ways of improving leak detection for plastic pipes. The project produced several improvements to acoustic equipment and practices, and also developed a new leak detection system called LeakFinder.

LeakFinder calculates a leak’s location based on the time it takes for a sound from a suspected leak to travel to two vibration sensors or hydrophones (underwater microphones) that brack
et the leak. It combines the advantages of acoustic detection with the power of a personal computer: a PC’s soundboard records and plays back leak signals, and its CPU filters interfering noise and cross-correlates the location.

Using Windows 2000, NT, 98 or 95, LeakFinder gives field-verified accuracy on PVC, cast and ductile iron, asbestos cement and large-diameter concrete pipes. It provides an adjustable playback speed for listening to otherwise inaudible low-frequency leak sounds in plastic pipes. It also permanently stores leak sounds for off-site re-analysis and evaluation. It is easily modified to incorporate hardware and signal processing advances, and can be integrated with commercial off-the-shelf equipment to provide a complete leak detection system.

“LeakFinder’s low cost makes it practical for users who can’t afford existing commercial systems,” says Dr. Hunaidi. For a demonstration of LeakFinder, visit www.nrc.ca/irc/leak/leakfinder.

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