Many underground infrastructure capital improvement projects are driven by capacity issues.
The South Surrey Interceptor project is no different. Work is wrapping up on Phase 2 of the Johnston Road Section of the project and — what many believe to be — the largest diameter microtunnelling project in North America.
The project owner, the Metro Vancouver Regional District (Metro Vancouver), manages approximately 530 km of trunk sewers for the 23 communities and serves approximately 2.5 million people in the Lower Mainland. When complete, the South Surrey Interceptor will collect sewage from South Surrey, White Rock and Langley and convey it to the Annacis Island Wastewater Treatment Plant.
The project is a twinning and is needed to enhance capacity and enhance environmental protection in the region. When the project is complete in 2022, Metro Vancouver can use both pipes to convey sewage, adjust flows as needed and even use one of the lines to hold sewage before delivering it to the treatment plant.
Johnston Road Section Phase 1, an open-cut section, was completed in December 2018. Phase 2 of the section began in June 2018 and consists of approximately 800 m of 3,050-mm ID (3,600-mm OD) reinforced concrete gravity sewer in Surrey, British Columbia. Key project challenges include tunnelling beneath business parks and city streets, bouldery ground and tunnelling near several utilities.
“The existing South Surrey Interceptor is a concrete box sewer that was constructed in the 1970s,” says Mike Jokic, senior project engineer for Metro Vancouver. “The twinning of the 10.5-km interceptor began in 1999 and these phases are the last of the project.”
The Johnston Road Section Phase 2 project was designed by Stantec Consulting Ltd. (Stantec) with Phase 2 microtunnelling handled by Ward & Burke Microtunneling Ltd. Stantec was also involved in preceding open cut sections.
Stantec’s original plans for Phase 2 called for two short tunnel sections totalling approximately 400 m and two open-cut sections. The originally designed open-cut sections were adjacent to buildings — approximately 10 m away — and across 152nd Street, a busy North-South route that intersects with British Columbia Highway 10.
According to Anil Dean, P.Eng., Stantec’s global practice leader for its water tunneling and trenchless practice, there were initial concerns about settlement and low cover — less than 2 m — that resulted in the two open-cut segment designs. However, a value-added proposal in the Ward & Burke bid submission eliminated those segments in favour of microtunnelling the whole stretch.
“We allowed several different construction methods to maximize contractor flexibility. We liked microtunnelling because of the ground and groundwater pressures through the glacial type materials, some of which were granular. Also, the water table could have been in the tunnel heading, so ideally, we wanted the contractor to use a technology that could handle the water bearing soil,” Dean says. “We had one curved alignment in the original design and Ward & Burke added a second curved alignment to Drive 4.”
Ward & Burke proposed the change in plans because it would make the project less expensive per metre, improve logistics and mobilization, stay within Metro Vancouver’s approved right of way and would only add one caisson shaft to the project.
“There were several benefits to Ward and Burke’s proposal. The main one was that it eliminated the open-cut section through the Benchmark Business Centre and across 152nd Street,” Dean says. “As you can imagine, open cutting with a 3,600-mm OD pipe, there is a lot of impact. With it being tunnelled, the only impact is through the four shafts.”
Jokic adds, “The main issue with crossing 152nd Street is that it is about 450 m away from the intersection with Highway 10. We would have had to completely close the road to get it done via open cut. We were also concerned about the 10 services in the road including a city sanitary sewer and an intermediate pressure gas line.”
Because this project marks Ward & Burke’s first in British Columbia, Metro Vancouver completed its due diligence before agreeing to go ahead with the adjusted plan. Jokic notes that similar Ward & Burke projects in Ontario and the United States gave Metro Vancouver the confidence that this was the right decision. He adds that even if the costs were equal, the decreased disruption of microtunnelling made this the way to go.
“The biggest reason we proposed microtunnelling the whole project was because of cost. For us to mobilize, from Alberta, for two short tunnel drives, it makes it far more expensive per metre, whereas we do the whole project (800 m) it was less expensive per metre for Metro Vancouver.” Cillian Cotter, main site engineer for Ward & Burke. “We were able to add a second curve to stay within Metro Vancouver’s right of way with the addition of an extra shaft.”
The project is divided into four drives with approximate lengths as follows — drive one is 370 m, drive two is 110 m, drive three is 40 m and drive four is 285 m — and the curved sections were in drives one and four.
Familiar Equipment, New Pipe
Ward & Burke is using a Herrenknecht AVN2500D, which they had up-skinned in Germany to a 3.6 m OD, two centrifuges for slurry handling and separation and a VMT guidance system for steering. Cotter notes that Ward & Burke has used this same machine on 2 m and 2.7 m projects in Alberta and Manitoba. Cotter notes that it is the success of these other projects — and the experience of its TBM operator — that they were confident in the success of this project.
To date, Ward and Burke has relied on Decast to supply its jacking pipe for Canadian projects, for logistical and costs reasons, the reinforced concrete pipe for this project is sourced locally.
“The big consideration, especially with a project going through the winter, is transporting the pipe through the Rocky Mountains,” Cotter says. “For us, that is a high risk if you have a bad winter, your pipe supply could be severely interrupted and could have a significant impact on the project.”
Ward and Burke worked with Langley Concrete Group in Chilliwack, British Columbia, about an hour away from the project on the jacking pipe manufacturing. This is the first jacking pipe Langley has produced and Ward and Burke provided the pipe specs and the mold, as well as assistance from the mold manufacturer.
“They grasped the production of the microtunnelling pipe quickly and have made high quality pipes for this project,” Cotter says. “The biggest consideration with this pipe is the logistics of making the pipe and transporting it to the job. Langley made the pipe for the open cut section, so that was not a concern.”
As with any large capital improvement project, challenges always come up. The only problems with the construction process happened during drive one beneath a less populated area and an arterial road.
“In this drive, we had clay over sand and we had some inadvertent returns while Ward & Burke was working out its grout and slurry pressures. Once they got the grout and slurry pressures adjusted, Ward & Burke, at times were going 12 to 15 m a day, which was good. They have used mostly one shift except in areas where the jacking pressures got too high, where they worked 24 hours.” Jokic says. “The inadvertent returns are less concerning than settlement, which was a big concern because of the low cover and we were tunnelling within 10 m of buildings.”
To address settlement concerns, the project called for a thorough settlement and vibration monitoring layout, which has yielded useful data about this machine’s vibration and noise levels that Ward & Burke will use on future projects, as well as valuable settlement data. At the more critical sections, Ward & Burke installed a hydroshield to help mitigate settlement and increase the tunnels stability.
Another challenge that cropped up post bid acceptance, but before the work commenced, was the Province’s Ministry of Environment decreased the threshold for allowable iron in soil; this meant that Metro Vancouver and Ward & Burke had to find a facility that not only could accept its wet spoils, but also one that was allowed to handle the iron laden soil. Though this was a headache, Jokic notes that had the project remained a mix of open-cut and microtunnel, the soil displaced would have been greater.
Despite these project challenges, Jokic says that installing the line via microtunnelling proved to be the right alternative. He doesn’t need to look any further than the meeting he attended with Metro Vancouver’s public information officer for the project. Jokic recalls that the owner of the business park — originally slated for open-cut — was not happy, but when they sat down to discuss the microtunnel approach they almost jumped for joy.
“Yes, it’s disruptive, but we have managed to keep the site as tight as possible. They may have lost some parking spaces, but there wasn’t a big trench dividing their business park in half,” Jokic says.
Microtunnelling is on track for completion in May, and Jokic says that Metro Vancouver is pleased with the project team and the progress made.