Project : Broadway Metro Extension, Millennium Line, Vancouver
In Vancouver, tunnel boring is underway for the Broadway extension to the Millennium Line, adding another 5.7km (3.5 miles) stretch to the city’s metro network with the mostly underground, east-west line, and six new stations.
The Acciona-Ghella joint venture has the design and construction contract for the Broadway extension project. They also worked together recently in Norway on long TBM-bored rail tunnels.
At the eastern of the line, the initial stretch, from the existing station of VCC-Clark out to the first new station, Great Northern Way-Emily Carr, is an elevated section.
Thereafter, the Broadway line runs underground to the west and has four intermediate stations (Mount Pleasant, Broadway-City Hall, Oak-VGH, and South Granville) en route to its end at Arbutus station.
Two 6m-diameter (19.7ft) Herrenknecht TBMs – ‘Elsie’ and ‘Phyllis’ – were launched from the first underground station in the east – Great Northern WayEmily Carr station – in early October and late November, respectively. Driving west, they have parallel 5km-long (3.1 miles) drives. They will pass through the four intermediate stations before finishing at Cypress Steet, near the future Arbutus station.
The machines are each expected to take about a year to complete their respective drives.
The overall Broadway extension project is due to be completed in early 2026.
Project: Site C Hydro
BC Hydro, a key power utility in the province and also a major player in both the Canadian and North American electricity markets, has its third large hydropower project under development on the Peace River, near Fort St John. The full name of the project is Site C Clean Energy Project and it is a large hydropower scheme in its own right, planned to have 1.1GW installed capacity to generate electricity from water stored behind a dam and spillway.
Contractor on the project is Acciona Infrastructures Canada and Samsung C&T Canada, in a 50/50 joint venture. Acciona is leader of the JV. The contract was awarded in Spring 2016 with a 96-month civils construction period.
Key structures to help facilitate construction of the Site C hydropower project included two large, if relatively short, diversion tunnels on a bank of the river channel. The parallel diversion tunnels were crucial structures for the construction phase as they take the river waters away from the dam construction site. With lengths of 700m (765yd) and 792m (866yd), respectively, and excavated widths of 12m (39.4ft) (14m (45.9ft) in spots), the tunnels were sized with sufficient capacity for pass flows safely and keep the dam site dry and safe, over the construction phase, as river levels vary with seasons.
A further role for the critical structures was to regulate flows during reservoir filling – which took a while, as the impounded body is about 85km long (53 miles). Once the river was impounded, the gates installed across the tunnel portals would be fully closed and the tunnels decommissioned, their tasks done.
But there was the challenge of excavating to be completed first.
The diversion tunnels are located in the rock of north bank of the river (left bank, looking downstream). The south bank houses the surface powerplant and spillway structures. To construct the tunnels, though the river also needed to be held back first, at the inlet area. With their inverts more than 20m (65.6ft) below the river level, cofferdams were installed into the river bed at each end of the tunnel to establish the construction zones for the inlet and outlet portals. The tunnels are 37m apart, at their centers.
While the JV designed a number of M&E elements as well as some temporary works for the diversion tunnels and final design of the cofferdam, BC Hydro was responsible for final design of the diversion tunnels, diversion inlet and outlet. The final size of the tunnels was 10.8m-wide (35.4ft) with thick concrete lining, cast by pouring with circular clip forms.
To construct the twin diversion tunnels, the JV used 4 x Sandvik roadheaders to excavate through bedrock geology consisting of interbedded siltstone, sandstone and shale of the Shaftesbury Formation. Exploratory adits in the area gave good site data for design. The shales are Cretaceous origin, generally dark gray and massive, and has 70 degree dip relaxation joints close to slopes and sub-horizontal bedding planes. The stratigraphy is similar on both banks of the river.
The bedrock is overlaid by fine-grained glaciolacustrine deposits and morainic silty and clayey diamictons, arising from the extended glacial history of the area.
With the Site C project in planning for some decades, and with more intensive ground investigation over 2009-2015, the project owner had undertaken a notable degree of site investigation. The work helped to establish that the diversion tunnels would be entirely in bedrock, generally with cover of about 80m, except near the portals.
While the glacial period is long gone, the region experienced very low temperatures of below -40°C during the works, adding to the tunneling challenge for the JV.
The roadheaders used on the job were 3 x MT520/023 (2 x new, 1 x refurbished) and 1 x MT720/084 (refurbished).
Opening up each tunnel in head and bench steps, the JV used the roadheaders to excavate downstream to take out approximately 180 000m3 (235 430yd3 ) of bedrock, in total. Each tunnel had a 6m (19.7ft) radius profile and flat bottom. The top benches were opened up to 7m-height (23ft) (60m2 (71.7yd2 ) face area), and the bottom benches excavated out the same face area again.
Excavation support was generally shotcrete layers with rockbolts, except for near the portals where steel ribs were also used. A further challenge was the demanding silica exposure controls.
For the final lining each diversion tunnel, slip forms (12m-long (39.4ft), self-launching) were used to cast concrete in 600mm (2ft) thick walls to create a circular finish. A total of 80 000m3 (104 636yd3 ) of concrete was poured from the telescopic distribution hose pipe. Contact grouting was then undertaken to fill any voids remaining behind the permanent concrete walls.
The JV undertook design and production of all mix designs for grout, shotcrete and concrete.
The two diversion tunnels were completed during the start of the covid pandemic and the river was diverted in Fall 2020.
While significant, the diversion tunnels were not the only tunneling works on the project. Other tunnels were excavated on the opposite river bank for groundwater drainage.
