MAY 2005 ISSUE
THE KEYSER FILE
A ‘Small’ Tunnel Project Earns Big Recognition
Edmonton’s South LRT Tunnel Presents Unique Challenges – and Wins Two CEA Showcase Awards
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BY Tom Keyser
Freelance Columnist
During a distinguished career in project management, Art Washuta, P.Eng., has worked on plenty of high-profile construction jobs. He has reason to be proud of each one.
Among them were the Oldman River Dam spillway, the environmental cleanup of DEW Line sites for the Department of National Defence, and the Anthony Henday Drive Southeast extension in Edmonton, to name a few.
But the Edmonton-based regional vice-president for UMA Engineering Ltd. professes a soft spot for one of his most recent efforts: the $30-million tunnel and portal project for Edmonton's south LRT extension, which captured awards of excellence in project management and in transportation infrastructure in the 2005 Consulting Engineers of Alberta Showcase Awards.
“Yes, that would rank right up near the top," agrees Mr. Washuta, whose company shared the honour with Stantec Consulting Ltd., the City of Edmonton's managing consultant for the project. “Just rubbing shoulders with the world-class experts we worked with was a pleasure as well as a learning experience.”
Mr. Washuta adds with a chuckle: “I wouldn't call it a huge project but it sure had its unique challenges.”
From Singapore in Pieces
Mr. Washuta isn’t kidding. Among the more startling of those unique challenges was the minor matter of importing a massive earth pressure balance tunnel boring machine from a remote job site in Singapore — piece by piece.
The enormous machine, manufactured in Etobicoke, Ont., by Lovat for its first application in 1999, crossed the Pacific by freighter. Once the expensive cargo reached Edmonton, technicians at
the site began the task of reassembly, a process that took several months.
But this tunnel boring machine was worth the time and trouble. Though he's managed tunnel projects in the past, Mr. Washuta was particularly impressed by the efficiency of the state-of-the-art monster.
As the name implies, the Lovat machine minimizes the risk of ground loss by balancing earth pressure at the tunnel face against the thrust pressure of the machine, while controlling the rate at which soil is removed by a screw conveyor.
The Trouble With Small
A number of other wrinkles set the LRT tunnel and portal project apart from the ordinary.
Right from the start, Mr. Washuta worried that it might be difficult to attract qualified private tunnelling contractors required to complete a project that could be considered small potatoes, in a relative sense. So the design team tendered the project in two different methodologies, in the hopes of creating greater contractor interest.
“Early on, we realized that both methodologies (either tunnel boring or sequential excavation) were perfectly feasible and cost-effective," he says. That freed up the team to go either way, depending on contractor response.
Meanwhile, his team advised the city to advertise internationally for expressions of interest and the effort drew a promising response: a dozen bites. A process of pre-qualification narrowed the bidders to six.
In the end, PCL-Maxam a Joint Venture came aboard as general contractor, with Aecon-McNally a Joint Venture acting as tunnelling subcontractor. The contractors booked on to a tricky job, because the geometry of the project presented problems.
“We had two tunnels, six metres in diameter and only
two to six metres apart. Within a distance of 300 metres for each tunnel, we had to contend with a 250-metre horizontal curve and a six per cent vertical grade," Mr. Washuta recalls.
“In addition, the tunnels traversed a number of different geological ground conditions. Plus we passed beneath a couple of buildings and a major utility services tunnel."
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Coming Through |
Subterranean Smorgasbord
As it dug its relatively short passage, the tunnel boring machine churned through a veritable smorgasbord of subterranean strata: dry sand, glacial clay till with wet sand layers, and finally Edmonton formation bedrock. Still, it forged its way towards University Station, twice.
The team had to keep close tabs on nearby buildings.
“I think we had 150 instrumentation points to monitor for building and ground settlement, as we were tunnelling under the University of Alberta Education Car Park and St. Joseph’s College. Every day we assessed the situation," Mr. Washuta says.
Settlement of the car park’s footings never exceeded 23 millimetres, which is “pretty remarkable.”
The TBM also had to proceed with extreme caution when their route took them beneath the 1960s-vintage utility services tunnel, which carries water, electrical and mechanical systems to the U of A.
It all adds up to just another “small" project, in Mr. Washuta's modest estimation. Clearly, the Showcase judges