Mississauga-based contractor Ward and Burke Microtunnelling Ltd. recently completed a pair of projects that further demonstrate the capabilities of microtunnelling. In October, the firm completed tunnelling on the Reconstruction of the West Don Sanitary Trunk Sewer project that involved a 250-m radius curve, the tightest curve completed in North American to date. In November, crews holed through on the 37th Street SW Storm Trunk Relocation, which at 2,500 mm ID, marks the largest microtunnel completed on the continent.
“The microtunnelling industry is strong at the moment in Canada,” said John Grennan, director of Ward and Burke Microtunnelling Ltd. “The market is driven by clients and consultants who are open to new technology and who want to work with microtunnel contractors in a collaborative approach. They are tired of problems with traditional open-face tunnelling below the water table in glacial tills, and they are moving to closed-faced technology where schedule and costs can be controlled and accurately predicted.”
The recently completed projects mark a trend of increasing innovation in the microtunnelling market across North America. The first curved drive in North America didn’t occur until 2010, with the first curved drive in Canada taking place in 2013. Longer drive lengths, compound curves, and now tighter radii and larger diameters increase the range of what can be accomplished with microtunnelling techniques. Longer distances and curves offer the benefit of fewer shafts, which creates less disruption and lowers the construction costs.
“A few years ago we would see a lot of jobs with open specifications, allowing the contractors to select the means and methods, but now we are seeing more and more jobs specified as microtunneling as owners have gained more confidence,” Grennan said.
Reconstruction of the West Don Sanitary Trunk Sewer
For this project, the City of Toronto needed to replace a sanitary trunk sewer located beneath G. Ross Lord Dam and Reservoir due to the deteriorated condition of the existing sewer that was built in the 1950s.
Ward and Burke was awarded a $12.3 million contract from the City of Toronto in April 2015. The project involved the construction of 787 m of 1,200- and 900-mm ID microtunnel including four deep tie-in shafts to relieve existing sewers under the reservoir that were in distress.
Ward and Burke began construction in May 2015, with access roads followed by the construction of the deep launch, reception and tie-in shafts. Cast in-situ concrete caissons were sunk at depths to 20 m on the project through glacial till consisting of silts, sands and gravels. Most tunnelling took place below 10 m of water pressure.
A key component of the project was the construction of the curved microtunnel around the existing dam wall. Due to restrictions with oil and gas utility corridors and overhead powerlines, a curved microtunnel with a radius of 250 m was required over a length of 350 m. Jackcontrol AG was awarded the subcontract to produce the hydraulic packer system from between each jacking pipe. Munro Ltd. produced the pipes for the project.
A Herrenknecht AVN 1200 MTBM with ancillary ITE Gmbh separation plant constructed all tunnels between July 2015 and October 2015. The job was a huge success, finishing three months ahead of schedule. Crews used VMT guidance equipment. The curved microtunnel is the tightest radius curved microtunnel in North America, according to Ward and Burke.
The job was specified as a microtunnel with the curve by WSP, the owner’s consultant, because surface conditions did not allow for the construction of intermediate shafts. The alternative to microtunnelling would have conventional tunnelling using an EPB TBM with segments, which would have resulted in a larger ID tunnel and increased costs.
37th Street SW Storm Trunk Relocation
In preparation for the construction of the southwest segment of the Calgary Ring Road project, the City of Calgary needed to relocate an existing trunk sewer. The project comprised 985 m of open-cut and 420 m of trenchless installation of 2,400-mm ID conduit. Whissell Contracting Ltd. was awarded the project by the City of Calgary in July 2015, and Ward and Burke was selected as subcontractor for the trenchless work as well as the construction of a 10.4-m ID x 15-m deep launch shaft.
Of the allowable tunnelling options —TBM tunnelling, open-shield tunnelling and microtunnelling — Ward and Burke opted for microtunnelling. Crews began launch shaft (reinforced concrete caisson) construction at the end of August 2015. A Herrenknecht AVN 2500 MTBM and ITE GmbH ancillary separation plant were mobilised from Toronto for the tunnel installation. The pipe was upsized from 2,400 mm to 2,500 mm to suit the existing machine.
To ensure that jacking pipe was up to standard, Munro Ltd. was awarded the subcontract to produce 2,500-mm ID RCP, which were hauled across Canada for the project. The huge logistical task was seen worthwhile given the microtunnel system dependence on quality pipe product, said Grennan. Munro Ltd. has been making pipe specifically for microtunnelling in its Utopia, Ontario, facility since 2012.
The ground presented mixed conditions, including 320 m through shale and 100 m through glacial till, which included silts, sands, gravels and boulders below the water table.
Microtunnel installation began Oct. 26 and was complete on Nov. 25, 2015. Maximum output obtained was 48 m in a day with all ancillary separation equipment able to keep up with the huge volume of muck.
The drive went without any issue and is believed to be the largest internal diameter microtunnel installation that has ever taken place in North America. What makes it even more notable is that the microtunnelling is still new in Calgary as the first microtunnelling project — the Bowness Sanitary Trunk — was completed in November 2014. That project involved more than 2 km of microtunnelling through ground conditions even more challenging than the 37th Street project, said Grennan, but its successful completion laid the groundwork for the record-setting 2,500-mm ID project.
“The fact that we were able to complete the Bowness project gave the city the confidence in the system,” he said. “When you have a few successful tunnels behind you then the fear of new technology and new systems is lessened.”