Vancouver is one of the youngest cities in the world. Like many of the western cities and regions of North America, it was founded and developed much later than its east coast counterparts — by nearly 300 years in some cases.
The city was incorporated in the late 19th century, and for the region as a whole, most of its rapid population growth has occurred in the 20th century. According to Metro Vancouver, an entity that acts as regional district, in the 25 years between 1981 and 2006, the region grew from a population of 1.3 million to 2.2M. Before 2040, the population of the Vancouver region is expected to grow by more than one million people.
For Metro Vancouver, how the region further develops is a significant undertaking, and it is no surprise public transportation is one of its priorities.
"The cities of Burnaby, Port Moody and Coquitlam have been planning for this line for the past decade and they’ve been developing mixed use, high-density transit-oriented development along the Evergreen Line corridor, so there is a lot of built up development for residential and commercial use that are looking to feed into the Evergreen Line," says Raymond Louie, technical director for the Ministry of Transportation and Infrastructure of British Columbia.
Being delivered by TransLink, the transportation authority for Metro Vancouver, and the Ministry of Transportation and Infrastructure of British Columbia, the 11km Evergreen Line extension to the region’s rapid transit system will cost CAD 1.4bn (USD 1.44bn). The project includes a 2km-long tunnel.
On January 29, BC’s Ministry of Transportation and Infrastructure announced it had awarded the CAD 889M (USD 865M) contract to design, build and finance the extension to EGRT Construction, an SNC-Lavalin-led consortium.
The contract is a turnkey design-build-finance package for all elements of the project including building the elevated and at-grade guideways, the tunnel, seven stations, power substations, train operating systems and other related facilities.
With the contract awarded, the ministry announced major construction should start in February, and the extension is expected to open in summer of 2016.
Speaking with Louie, he explains the Evergreen extension will connect three cities, Burnaby, Port Moody and Coquitlam and the best way to do this is via Clarke Road.
"However the Clark Road alignment in this portion has grades of up to 12 per cent and the rail rapid transit vehicles that we are using can only handle maximum grade of 6 per cent," he says.
The 2km tunnel will cut through the hills in a single bore, 10km in diameter, with a dividing wall separating the inbound and outbound guideways. Depth will range between 17m and 55m. A geotechnical investigation including 24 boreholes along the tunnel alignment concerned twin tunnels. EGRT presented the option of single bore to avoid excavating cross passages, which reduces risk and provides a schedule advantage.
Louie says the ground conditions have been the biggest challenge to the design. "The soil conditions in this area are quite challenging. We’ve got a good team that has a good understanding of the soil conditions, and designing and constructing in those conditions.
"It’s not the easiest tunnel to construct with the mixed ground conditions, or the water pressure."
The tunnel with pass through mixed layers of glacial till with deposits, which consist of sands, silts, clays and gravels.
"We also expect a mix of cobbles and boulders within these layers, including granite rocks. Also, we expect fairly high water pressures. We’re expecting approximately 3 bars of pressure."
He adds, "The soils along the bore tunnel alignment also have minerals that are abrasive, such as quartz. Also, we may expect soil units containing clingy soils, which can create adhesion and clogging difficulties when excavated with a closed TBM."
The detailed tunnelling design is still underway according to the specifications set out by the client. EGRT Construction is procuring a TBM from Toronto-based Catepillar Tunneling. A spokesperson for the consortium says final discussions with CAT are still underway regarding the machine, which will operate wholly in EPB mode to balance the variable ground/water pressure. For the tunnel lining, a reinforced precast solution is being considered and it is planned to precast the units locally in BC.
Delivery of the TBM is expected in late 2013 and EGRT is planning to launch the machine at from the north portal. The launch site is still under final design, though EGRT says this is a confined site that will accommodate the appropriate ‘craneage’ to safely handle the TBM assembly, which will happen on a pre-constructed launch pad. The final back up sections will be added as the machine advances.
