Paula Wallis, TunnelTalk

Metro Vancouver is preparing to tender the construction contract on a new water tunnel, and is days from issuing a request for proposals for preliminary design on a second tunnel. The deep water tunnels are key components in a Can$600 million system upgrade designed to protect the region's main water supply in the event of a major earthquake.

Fig 1. Port Mann Tunnel alignment

The 1,000m long x 3.2m diameter Port Mann tunnel will run under the Fraser River conveying water in an internal welded-steel pipe from Coquitlam to North Surrey (Fig 1).

The design team has completed the detailed design and Contract Manager, Hatch Mott MacDonald, is currently doing a risk review, said Frank Huber, Division Manager of Engineering Support and Technical Services with Metro Vancouver. "We hope to have the pre-qualification documents ready in the next few weeks and the issue of an invitation to pre-qualify released by the end of October 2009. In the New Year we expect to have a short list of three or four contractors and, at that point, tender the work with the expectation of mobilizing by spring of next year." The design team is the Fraser River Tunnel Group consisting of Sandwell Engineering, Jacobs Associates and Golder Associates.

The pipeline crosses the Fraser River downstream of the Port Mann Bridge and is a primary water supply link to communities south of the river. The single construction contract, valued at roughly Can$100 million, will include, two 60m deep shafts on either side of the river, the tunnel, and the lining.

"The geology along the alignment is mainly clays and till-like deposits," said Huber. "There are a few short stretches of more granular material, but I would say 90% is either clay or till-like. There will be a couple of challenges, especially with the sinking of the shafts, which are are quite deep, and the contractor will have to deal with artesian pressures. Water pressure of up to 5 bar are also expected along the alignment."

Huber said design engineers are still debating whether to specify an EPB TMB or leave it up to the contractor to decide between EPB or slurry excavation. "The capabilities of both types of machines overlap now days and our consultants are still debating which machine will be best suited to the tunneling conditions. We will make a decision before the contract is tendered."

Fig 2. Second Narrows Tunnel

Unlike other Canadian clients, including the Toronto Transportation Commission for its new Spadina Line metro extension, and the Regional Municipality of York for its Southeast Collector Sewer (SEC) just north of Toronto, Metro Vancouver does not plan to purchase the TBM ahead of the contract. "The shaft sinking will provide sufficient lead time for the contractor to select and order its own machine," said Huber.

The Second Narrows tunnel is moving from the conceptual to the preliminary design phase. This 1100m water tunnel will be the primary supply link from the Seymour watershed across the Burrard Inlet to Burnaby (Fig 2). "Metro Vancouver is two or three weeks away from putting out requests for proposals for preliminary design on the Second Narrows Tunnel," said Huber.

This larger, 4.1m diameter, tunnel crosses under the Burrard Inlet with the southern portal located in northwest Burnaby and within city-owned land at Montrose Park. Metro Vancouver hopes to expedite the design phase to start construction of this tunnel in three years. Meantime construction on the Port Mann Tunnel is scheduled for Spring 2010 with a completion date of 2013.

Meanwhile, Metro Vancouver has confirmed that Frontier Kemper has mobilized on its contract to take over of the public authority's Seymour-Capilano twin water tunnels project after terminating the initial construction contract in May 2008. Frontier Kemper is awarded the contract to compete the 3.8m diameter TBM drives using the two new Robbins TBMs purchased by Bilfinger Berger for the original construction contract that came to a standstill in January 2008 due to claimed unsafe tunneling conditions and eventual termination of the contract. Frontier Kemper will complete the 7.1km long tunnels from their current mid-point progress to the Capilano end of the deep twin tunnel drives. Tunneling resumed on the treated water tunnel in July 2009, and the raw water tunnel in August 2009. The project has a scheduled completion date of Spring 2013.

References

Toronto Metro gears up for tender - TunnelTalk, Sep 2009
Client EPBM order to jump-start sewer project - TunnelTalk, Sep 2009
Rebid reprieve for Seymour Capilano - TunnelTalk, Jan 2009
Vancouver's twin tunnels contract terminated - TunnelTalk, May 2008