Jumbo Repair

The City of Victoria finds a winning trenchless strategy for a major rehabilitation project on a critical 5-mile-long water transmission main

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The City of Victoria, B.C., is undertaking the replacement of a 5-mile stretch of 20- to 24-inch steel water main installed in the 1920s, 1930s and 1940s — believed to be the largest trenchless program of its kind in Canada.

 

The deteriorated condition of the main and the affected distribution lines convinced the city that only a rapid-fire program of trenchless rehabilitation and replacement on a large section of line would serve city residents and businesses.

 

“Essentially, the process started in September 2001, when we had a geyser coming out of the road from one of the mains in the worst-affected areas,” says Bruce Kerr, project manager for underground utilities with the Engineering Department.

 

“When we dug down to see how bad the condition of the pipe was, visual inspection showed that the pipe had old welded-on patches. The engineering people started talking with the operations people, and we realized something had to be done.”

 

The city completed most of the repair with a modified slip-lining process using a folded, pulled-in-place HDPE liner system. The first phase of the repair is complete, and the second and final phase was to be finished in spring 2010.

 

Assessing the issues

Victoria is the capital of British Columbia, one of 13 municipalities that comprise the province’s Capital Region District, which in turn is responsible for the area’s sewer and water supply. While the District oversees the supply and purification of water derived from nearby Sooke Lake Reservoir, distribution is the responsibility of each member city.

 

An extensive review by the Engineering Department from 2002 to 2003 showed that some areas of the city were built on corrosive soil with high acidity. “In those areas, pieces of the road were settling, and we could see water showing up on the surface,” says Kerr. “Often, where we were finding the ground was wet around the mains, there weren’t any obvious leaks. The pipes were pitted like a soaker hose of pinhole leaks.”

 

In 2004, the Engineering Department retained Levelton Engineering Ltd. of Richmond, B.C. to prepare a report on the life expectancy of the mains. With few exceptions, the firm’s recommendations involved replacement and rehabilitation, ranging from immediate to within about five years.

 

A water-distribution system computer model prepared by the Engineering Department found that the existing mains provided enough capacity to meet current and future needs. The city established a reserve fund in 2006 to finance construction in advance of the project start.

 

“We told the consultant that we favored the use of trenchless technology wherever possible, not only because it would save time and money and reduce traffic congestion, but because it would reduce the impact on the city’s tree canopy and reduce the total amount of carbon emissions when compared to open-cut,” says Kerr. The consultants reported that about 90 percent of the work could be done using trenchless technology.

 

Construction staging

Staging the repairs provided the next challenge. The targeted area of the water system consists of a series of regulated and unregulated mains. Work had to be scheduled so as to provide a consistent water supply at adequate pressure during repairs.

 

“We split the project into two phases,” says Kerr. “We decided to work backwards from the source — the municipal boundary where the Capital Region District main supplying water enters Victoria. The plan was to get the lines downstream ready first so we would be in good shape to maintain flow as we worked upward to the source.”

 

The city chose the office of Insituform Technologies Inc., in Edmonton, Alta., to handle the trenchless rehabilitation. Burnell Contractors of Cobble Hill, B.C. took on the open-cut work as a subcontractor. A city arborist worked with the contractors to ensure maximum health and survival of trees during construction.

 

Phase 1 of construction involved a 2.8-mile section between the city’s Hillside Avenue and Pandora Avenue. “We were converting about 1.5 miles of the main from regulated to unregulated pressure,” says Kerr. “The open-cut phase of the project began in November 2008. We had to make some system improvements, including the open-cut replacement of some sections of main with ductile iron, and the installation of a pressure-relief valve station to strengthen the integrity of the overall water-distribution system.”

 

Redundant main retained

The first section slated for attention was a regulated main on Pandora, located farthest from the water source. “Our computer model showed that the system derived no real advantage from that main, so we decided we would temporarily convert it to an unregulated main, so we could maintain water service during construction,” says Kerr.

 

“When we found out that the main was actually in pretty good shape, we decided to leave it operating as a permanent unregulated main that would provide redundancy to the distribution system. It essentially turned the water system from a series of branches into a loop.”

 

The city also had to examine one of the system’s oldest components, a series of butterfly valves installed as long as 80 years ago. While some of the valves passed muster, the engineers decided to replace every valve along the route before trenchless rehabilitation could begin.

 

Communication with the contractor was critical, says Kerr. Because the system was so complex, city engineers had to remain in constant contact with Insituform to ensure that the correct valves were being open and shut to isolate the target pipe segments and to maintain the city’s water supply.

 

Modified slip-lining

Rehabilitation, which began in March 2009, used InsituGuard®, a close-fit, modified slip-lining process. Since the smallest internal diameter of the affected mains measured 500 mm, the liner was designed to a diameter of 494 mm, offering a 6-mm leeway.

 

Under the process, a cross-section of a circular HDPE liner is temporarily folded and lubricated with a bentonite slurry to permit insertion to the host pipe. Plastic bands maintain the folded profile of the liner while a winch pulls it into place. Exposed bands at both ends are then cut and Kevlar-reinforced air bags are inserted to the liner to expand it to a round shape. Liner ends are then restrained and capped with flanges before the liner is pressurized to 160 psi to expand it to its full diameter.

 

Camera inspection showed that the steel main was coated on the inside with coal tar enamel. The mains were cleaned out using high-pressure jets, and a chain flail to remove encrustation at welded pipe joints. A robotic router was sent into the main to smooth out any imperfections that might damage the liner or cause it to hang up. “We also found a section of main that was finished with a cement-mortar lining,” says Kerr. “Luckily, its thickness fell within the tolerances we required to insert the liner.”

 

Smooth operation

Phase 1 of construction went off without a hitch, ending in December 2009. “The only delay we had was in getting a delivery of some Viking Johnson flange adapters that needed to be specially ordered from England,” Kerr says. “These were required to marry up the liner and the steel mains, but they took a few weeks longer to manufacture than we had anticipated. The contractor actually had to fly in a few of the units from England so we could get that part of the work started.”

 

Phase 2 of construction, scheduled to begin in spring 2010, couldn’t have been staged more advantageously from a fiscal perspective. The Canadian government’s Federal Provincial Infrastructure Grant program, launched as a stimulus measure in 2009, favored shovel-ready projects that could be completed by the spring of 2011.

 

Instead of shouldering the full budget of this phase of construction, the grant will allow the city to share the costs evenly with the province and federal government. The project specified trenchless rehabilitation.

 

“On this 2.2-mile phase, there will be virtually no open-cut at all, although the line is largely regulated, so we’ll need to dig a lot more holes to make service connections,” says Kerr. “Judging from our experience with the trenchless work in phase 1, we should be able to meet the government deadline for completion in 2011 without any problem.”



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