Shani Wallis, Editor

Three bids were received in early August for the 7.6km deep TBM-driven water tunnels in Vancouver. Lowest at $99.65 million is a bid from the Bilfinger Berger/Frucon JV. Second is Frontier Kemper/AECON at $186.24 million and highest at $237.54 million is from Peter Kiewit & Sons.

The contract covers excavation of twin 3.5m (I 1ft) o.d. rock TBM tunnels for the new SeymourCapilano Filtration Project for the Greater Vancouver Water District (GVWD). Raw water will be pumped from the Capilano reservoir to the Seyour watershed filtration plant through one tunnel and treated water will flow by gravity back through the second tunnel to Capilano and into the distribution system.

Designed by the Toronto office of Hatch Mott MacDonald for the client's overall program manager SNC Lavalin, the tunnels pass through granite bedrock characterized by deep U-shaped valleys filled with extensive glacial deposit. Driven between deep access shafts, the tunnels lie at up to 640m (2,099ft) deep. High quality granite/ granodiorite bedrock of up to 250MPa and generally greater than 75% RQD will allow substantial portions of the tunnels to remain unlined.

Two TBMs are needed to meet the GVWD's 2006 project completion date. Both will drive from a 185m (606ft) deep access shaft at the Seymour working site. At the Capilano end of the drives, two 3.5m (11ft) diameter shafts of about 220m (721ft) deep will be raise bored.

Andy Saltis, Project Manager for GVWD said the bids are now in review and evaluation before contract award.

Shani Wallis, Editor

More than 7.6km (4 miles) of deep TBM-driven tunnels will provide cleaner, better tasting drinking water to more than a million customers in the greater Vancouver area. Contracts for the new Seymour-Capilano Filtration Project are scheduled to be advertised in April with bids returned about eight weeks later; award announced in July; and work starting in August.

The project area's Cleveland Dam spillway

The project will link the Capilano and Seymour watersheds east and west of Grouse Mountain respectively. Located in Northern Vancouver, they are the primary watersheds for the Greater Vancouver Water District GVWD). Twin 3.5m (11ft) diameter tunnels will connect a 1,200 million liter/day (ml/day) pumping station to an 1,800ml/day filtration plant more than 4 miles away. The pumping station at the Capilano reservoir will send raw water through one tunnel to the filtration plant in the Seymour watershed. Gravity will then feed the treated water back through the second parallel tunnel to Capilano and into the distribution network.

New federal and regional water quality standards, lower turbidity requirements, and future demand are the forces driving the project. Within the overall project estimate of Can$600 million, tunnel excavation is estimated at roughly $100 million. The site is located across the Burrard Inlet from downtown Vancouver in the Pacific Ranges subsection of the Coast Mountains - region heavily modified by glaciation characterized by granite bedrock. Deep U-shaped valleys between sharp, high mountain peaks and lower rounded peaks are in-filled with extensive glacial deposits. These deposits cover relatively deep buried valleys at both ends of the tunnel alignment.

The Toronto office of Hatch Mott Macdonald (HMM) was retained to carry out preliminary studies for project definition and confirmed the preference for deep tunnels in bedrock for conveyance. "The tunnels will lie at a maximum depth of 640M (2,099ft)," said Brian Garrod, Project Engineer for HMM. "The high quality granite bedrock means substantial portions of the tunnels will be unlined although the deep glacial deposits at each end of the tunnels will require deep access shafts and reaches of in-situ concrete lining."

Working with SNC Lavalin, overall program manager for the filtration project, HMM has also completed the geotechnical site investigation. It is now completing the final design for the twin tunnels and will provide engineering services through the construction phase. Final design was about 90% complete when TunnelTalk contacted HMM's head office in Toronto in late February.

The predominant rock type on the tunnel alignment is a strong granite/granodiorite. Unconfined compressive strength tests on initial samples are in the range of 80 to 250MPa. This is reflective of the mineral assemblage and the degree of alteration. The geotechnical report describes the rock quality as good to very good with a rock quality designation (RQD) generally greater than 75% which is typical of good quality granite.

While the ground water table is near surface, initial borehole packer testing indicates a low rock mass permeability. Phase 11 of the geotechnical study however raised serious questions about the location of the proposed 12m diameter Seymour Shaft. High groundwater flow rates in about 100m of water-bearing overburden were found. "We initially considered ground freezing," said Garrod, "but this proved too costly, so we looked at alternative shaft sites. After evaluating 10 different sites we decided on a location about 250m (820ft) from the original site. The bedrock at this location is about 30m (98ft) below surface and pipelines will be installed to connect to the filtration plant."

Investigating conditions along the tunnel route

The selection of the tunnels' vertical alignment is driven by the requirement to pass with adequate rock cover beneath the two buried valleys. The geotechnical study showed significant variability in rock surface profile with bedrock depths in excess of 600m (1,968ft).

The tunnels will run in bedrock between 160m (524ft) and 640m (2,099ft) below the surface. Sections of steel lining are specified for zones in which the measured stress levels in the host rock are found to be inadequate to prevent hydraulic leakage.

Because of significant restrictions on construction at the environmentally sensitive residential Capilano end, the Seymour end will serve as the working site and launch shaft for two TBMs required to meet GVWD's project schedule. The shaft will be about 185m deep and 12m diameter and the tunnels will be driven on a 2%+ downhill gradient.

A minimum 3.5m (11ft) excavated diameter was selected for the tunnels to provide sufficient clearance for the installation of initial support in poor quality rock. This diameter will also accommodate a minimum 3m (10ft) diameter inside final lining. At the Capilano pumping station end, two 3.5m (11ft) diameter raise bored shafts will be constructed. Again, because of the depth of the buried valley, these shafts will be at least 220m deep.

As work on the new filtration plant gets underway, tree clearing and site grading started near the Capilano Reservoir Cleveland Dam in late January 2004. This phase will include some controlled blasting.

The tunnel construction contract will contain risk-sharing provisions including a Geotechnical Baseline Report, a Differing Site Conditions clause, and a Disputes Review Board. "Completion of the design phase is only days away now," said Goran Oljaca Senior Engineer with GVWD. "The pre- qualification process closed early in February and we received eight requests for qualifications (RFQ). We are on schedule to advertise the contracts in April and open bids about eight weeks later. We hope to award the tunnel excavation contracts in July and for work to start in August." If all goes as planned safer, better tasting water will be flowing to GVWD customers by 2006.