In Canada, significant investment has been made over recent years to develop a variety of new tunnel projects for transport projects but construction of underground assets to provide or support conveyance of utility services also have been in development in the Toronto and Vancouver areas.

In Toronto, one of the recently completed major tunnelling jobs was excavations for the Ashbridges Bay outfall tunnel, undertaken as part of construction of a replacement wastewater treatment project for the city.

Over in British Columbia, in Vancouver, there is a large programme of capital spend underway for the phased construction of new tunnels to carry water mains. With the region having seismic risk, the projects are required to improve the resilience of the water supply network in the expanding coastal city.

The utility, Metro Vancouver, has completed one water supply tunnel (WST) project and it is well advanced on building a second (Second Narrows), while construction activity is beginning on a third (Annacis) and it has planning underway for yet another (Stanley Park).

Elsewhere in BC, recent tunnelling work has involved finally completing a second, for years only partly-built, water tunnel for the Kemano hydropower facility, owned by mining company Rio Tinto.

At another hydroelectric power plant site, the provincial energy company BC Hydro is developing the Site C facility that requires underground works. Sticking with energy in the province though, but natural gas this time, a contract was recently awarded to construct a tunnel that will carry pipelines for the Eagle Mountain- Woodfibre project.


Project: Ashbridges Bay outfall

At Ashbridges Bay, Toronto, the 70-year old treatment plant and its outfall discharging treated effluent into Lake Ontario constitute one of the oldest such facilities in the city and the entire country. In addition to problems of age, the facility does not meet discharge standards nor has it sufficient capacity for modern needs, and it is also approaching the end of its service life.

More investment was required from the city to overcome the problems. But the capital spend will bring improvements in water quality of the lake and to its shoreline and beaches, which will also bring benefits to the economy of the region.

The resulting choice made by the City of Toronto is to have a new wastewater treatment plant along with a new 3.5km-long (2.2 miles) outfall tunnel, which will convey treated effluent up through 50 vertical risers and ports at its end for diffusion into the lake waters.

Hatch undertook the design, project and construction management for the Ashbridges Bay wastewater treatment project, including preparation of contracts with the geotechnical baseline report (GBR) – which included baselining marine conditions to reduce contractor risk.

The contractor awarded the job is a joint venture of Southland/Astaldi. For construction of the outfall tunnel, that passes offshore under the lake, the JV chose a Robbins single shield TBM. The machine was launched from an 85m-deep (279ft), 14m i.d. (46ft) shaft, in Spring 2021.

Before launch, the 7.95m-diameter (26.1ft) machine had already won plaudits for its entirely remote acceptance, performed during the covid pandemic. The TBM was assembled in Mexico and detailed communications work with the US and Canada enabled the all-remote achievement, which won praise from the Tunnelling Association of Canada (TAC), in late 2021

On the tunnelling project, the TBM bored through geology comprising mainly shale with other sedimentary rocks – limestone, siltstone and sandstone. The tunnel is entirely within the Georgian Bay Shale Formation, and such shales in southern Ontario have been known to cause time-dependent deformation (TDD) and this factor had to be accounted for in the design of the 7m (23ft) i.d. concrete segmental lining.

During tunnelling, the JV’s crews worked 2 x 12- hr shifts on weekdays. A Robbins-made continuous conveyor for muck removal also included vertical transport up the shaft. The TBM achieved best daily progress rates of up to 47m (154ft), or 30 rings.

The excavation sequence included probing ahead every 25 machine cycles. Only seven cutters were changed on the drive and wear was low, at 2mm- 5mm, surprising the tunnelers. However, when the machine reached the final stretch of the tunnel – along the portion that would house the vertical risers – the advance was hindered by groundwater ingress, calling for extra probing and grouting measures, says Hatch.

The JV’s project manager, Joe Savage, said of the challenge, in a statement: “The team really worked together to overcome some tough ground conditions and high water inflows.”

Tunnelling was successfully completed in early 2022.


Projects: Metro Vancouver’s water supply tunnels

Metro Vancouver’s existing water supply mains went into service over 1940s-1970s but they are vulnerable to earthquake damage as well as nearing the end of their service lives. As the utility serves up to 2.7 million people, it is improving the seismic resilience of its regional water supply network by building a number of new deep tunnels to hold new water mains.

The WST projects so far are: Port Mann, Second Narrows, Annacis and Stanley Park.

Port Mann WST

The first of the water supply tunnels (WST) to pass below marine waters was the Port Mann project, for which TBM tunnelling was performed under Fraser River and completed in mid-2015. The finished project went into service in 2017.

Underground works on Port Mann WST involved the excavation of two 60m-deep shafts to enable a 3.5m-diameter (11.5ft) tunnel to be bored approximately 30m (98.5ft) below the river bed. The 1km-long (0.63 miles) tunnel is between Coquitlam’s Maquabeak Park on the north shore and CN Thornton Yard on the south side, in the City of Surrey. The completed tunnel carries a 2.1m-diameter (6.8ft) steel water main.

Second Narrows WST

The 1.1km-long (0.7 miles), 5.8m i.d. (19ft) segmentally lined water conveyance tunnel runs 30m (98.5ft) under Burrard Inlet. Contractor for the project is Traylor-Aecon, which was awarded the job in late 2018.

Metro Vancouver said main tunnelling was performed with a 6.69m-diameter (21.9ft) Herrenknecht Mixshield/slurry TBM that set off from a 50m-deep (164ft) shaft in August 2020. The TBM drive proceeded from north side of the inlet (District of North Vancouver) to the south side.

Geology along the alignment comprises three distinct geological zones – sand and silt mixtures; a soil-torock transition zone with cobbles and boulders; and, mostly weak sandstone.

A little over a year after the TBM launch, the utility announced completion of main tunnelling work, in Winter 2021. The machine had reached the more than 100m-deep (328ft) shaft on the south side of the inlet, in Second Narrows Park, in the City of Burnaby.

Following main excavation of the shafts and tunnel, the construction project has had three steel water mains (2 x 2.4m dia (7.8ft), 1 x 1.5m dia (4.9ft)) installed and then backfilled with concrete, plus new valve chambers built, connected to the existing water system. The project is expected to be completed in 2025, says Metro Vancouver.

McMillen Jacobs Associates is Engineer of record for the underground structures and prime consultant for the design team, which also included Aecom and WSPGolder.

Mott MacDonald Canada is construction manager with Jacobs as sub-consultant.

Annacis WST

The 2.35km-long (1.46 miles) tunnel will run below the Fraser River between the City of Surrey and the City of New Westminster. At the beginning of 2022, while still working on the Second Narrows project, Traylor-Aecon was awarded the Annacis WST contract to excavate the shaft and tunnel as well as undertake installation of a single water main, valve chambers and surface pipework.

Early site activities have been getting underway. Tunnelling will be undertaken from an entry shaft (45m-50m deep (147.6ft – 164ft)) in Surrey to the exit shaft (60m deep (196.8ft)) in New Westminster. The TBM’s northward drive will advance at a depth of approximately 50m (164ft) below the river level.

Design for the project began in 2017. The main construction period is late 2022 to 2027 for final completion. Ancillary structures include a large underground box, 8m-deep, to house the control valve. The tunnel is to hold a 2.6m dia (8.5ft) steel water main. Landscaping/ restoration of the project sites is due by 2028.

Stanley Park WST

The next major new WST, to replace one of the oldest water mains, is to run below Stanley Park and has reached detailed design stage, says Metro Vancouver. The water system received supplies coming in by pipeline from the network running below Burrard Inlet.

This project, however, calls for three shafts and two linked tunnels. Unlike the other WST projects, this tunnel will stay onshore as it carries the new water main below the park. There will also be two underground valve chambers.

Procurement for the construction stage will commence in the near future.

The project schedule now anticipates construction getting underway by the end of 2023 or early 2024. The programme was recently pushed back by more than a year but the planned completion date remains as 2028, says Metro Vancouver.

The development work for the Stanley Park scheme began in 2016 with conceptual design that lasted until mid-2018. Immediately following after came the preliminary design work, until Fall 2019, and then detailed design began.

Project: Kemano Hydro

Rio Tinto has added a fully completed, second water conveyance tunnel (T2) for its Kemano hydropower plant, which generates electricity for an aluminium smelter in Kitimat.

The 16km-long (10 miles) tunnel was partly built for some decades, beside the first fully completed and operational tunnel (T1) constructed in the 1950s to tap Tahtsa Lake.

Early development of T2 saw only a stub tunnel built alongside T1 and it was not until the 1990s that more excavations took place in earnest toward completion of the second hydro tunnel. By 1995, however, when T2 was about half-built with 8.4km (5.2 miles) constructed, the tunnel works were halted. Excavations did not to resume for 23 years.

The main works to complete T2 involved excavation of the final 7.6km-long (4.7 miles) stretch. The tunnelling works were performed over 2018-2022, undertaken by Frontier-Kemper/Aecon joint venture. Hatch was the designer.

A Herrenknecht TBM was used to bore the final stretch of T2 but the tunnelling works also included some drill and blast excavations.

The recent completion activities on T2 has also included refurbishment of the first stretch of the tunnel that was built and left dormant.

Project: Eagle Mountain-Woodfibre gas pipeline

Frontier-Kemper, which is part of the Tutor-Perini construction group, is working on another energy project in BC that requires underground works. Working with Michels, the JV has a contract from FortisBC Energy, Inc, to build a tunnel to house a 24” natural gas pipeline for the Eagle Mountain-Woodfibre project, located at Squamish.

Contract award was in Spring 2022. Main works for the approximately 9km-long (5.6 mile) tunnel portion of the pipeline project are due to start on site in 2023. The project is to use two TBMs to excavate the tunnel, which has different geological conditions and cover as the route runs across part of Squamish, from the Woodfibre LNG industrial site.

The tunnel is to be constructed at depths varying from 25m-450m below the varying ground surface. While most of the excavation will be by tunnel boring there will be some drill and blast, said Frontier-Kemper.

The stretch of tunnel with higher cover is where the alignment passes below a hill, near the LNG industrial site. This 5km-long (3.1mile) section is to be bored by a 4.5m-diameter (14.8ft) hard rock TBM.

The remaining 3.8km-long (2.4 mile) section has shallower cover but passes below the Skwelwil’em Squamish estuary and wildlife management area, calling for tunnelling boring by 4.1m-diameter (13.5ft) slurry machine.

The tunnel will hold two gas pipelines and the entire project is expected to be substantially completed by Fall 2025.