Over two years ago, twin Robbins TBMs sat idle for 18 months, hundreds of metres below North Vancouver, British Colombia due to a ground conditions dispute. Completion concerns about Metro Vancouver’s Seymour Capilano twin tunnels have now been addressed following the successful restart of the 3.8m diameter machines in July and August 2009. The TBMs completed tunneling on 4 November, 2010, capping off the final 3.1km of excavation in each tunnel ahead of the revised schedule.
The project’s second contractor, the Seymour Cap Partnership (SCP – a JV of Frontier-Kemper Constructors ULC, Aecon Constructors and JF Shea) achieved up to 29m per day with both machines in sometimes difficult ground conditions, including stress release events and faulted and sheared rock. “We are all miners at heart here. When someone else says something can’t be done, we show them that it can be. This should be taken as a big pat on the back for all those involved,” says Richard Boutelle, Special Projects Manager for Frontier-Kemper.
Project Background
The Seymour Capilano Water Filtration Project, for owner Metro Vancouver, is part of a large scheme to improve the quality of drinking water in Vancouver, British Columbia. The completed filtration system will clean 1.8bn litres of water a day and will lower the water turbidity (cloudiness) and micro-organism levels to meet federal standards for drinking water.
The project design consists of parallel tunnels connected to deep shafts at either end. One tunnel will pump untreated water from the Capilano Reservoir to a filtration plant in the Lower Seymour Conservation Reserve. The second tunnel will return treated water to the Capilano Area Water Transmission Mains for public consumption. Once in operation, the two tunnels will be pressurised. A gap of 100m between the tunnels will prevent crossflow, while 0.6 miles (1 km) of steel lining at either end of each tunnel will prevent leakage where they converge at the shaft sites. The 4.5km of tunnel in between will be lined with a layer of sprayed concrete.
The deep tunnels are up to 640m below the surface at a 2.3 per cent downgrade, a design taken to avoid two unstable glacial valleys identified during geotechnical surveys. The glacial deposits are quite extensive, requiring the relocation of the initial site of the Seymour shaft after investigations revealed 100m of water-bearing glacial material and shattered bedrock. The chosen site for the shaft is in more stable rock, and the tunnels are located entirely in granitic and metavolcanic geology up to 285MPa UCS.
Project startup and machine launch
While excavation would normally start from the Capilano end, allowing the TBM bores to proceed uphill, launch was instead planned at the Seymour shaft to minimize public impact. The Capilano shaft site has a small available footprint and is located very close to a residential area and popular park. The Seymour location offered a large site area and muck storage close by, with minimal effects to the environment.
The site of the Seymour shaft, tucked away in dense evergreen trees at the base of the North Shore Mountains, features a unique crane system suspended over the 185m-deep, 11m-diameter shaft. The crane features two 70-t hoists that were used to lower TBM components down the shaft, and that are now used as elevators for crew members and for removing spoils from the tunnels in two buckets of 30m3 capacity. Six trains of side dumping muck cars (three for each tunnel) were designed for removal of the spoil at one train for every 1.5m TBM stroke.
Both Robbins machines were launched from a common cavern in July and September 2006 to bore the parallel 7.1kmlong tunnels. The two 3.8m-diameter Robbins High Performance (HP) Main Beam TBMs were supplied to the original contractor, Bilfinger Berger (Canada). Both machines came equipped with 26 cutters of 19-inch (482 mm) diameter and installed power of 1,250 kW (1,675 HP).
Machine assembly took place in very short starter tunnels at the bottom of the Seymour shaft. The first TBM, for the raw water tunnel, was launched from a 60.5-m starter tunnel and the second TBM, for the treated water tunnel, was launched from a 70.5-m starter tunnel. Because of the short tunnel lengths, both TBMs began excavation with just the first 11 of their 35- section back-up systems installed.
Initial tunnelling
The project’s initial contractor, Bilfinger Berger (Canada), had excavated approximately 50 per cent of the raw water tunnel and 45 per cent of the treated water tunnel by mid-January 2007. At the time, Bilfinger Berger cited challenging blocky and weak rock conditions as a safety concern to its crew and ordered a halt to work in the tunnels. Owner Metro Vancouver responded to concerns by developing a revised ground support program with designer and consultant Hatch Mott MacDonald. The owner’s dispute with Bilfinger Berger resulted in a termination of contract; the case has a hearing date of November 2011 in British Columbia’s Supreme Court. The Seymour Cap Partnership was awarded the new completion contract in April 2009. Following maintenance of the machines, excavation restarted after an 18-month delay.
Surmounting granitic ground
Frontier-Kemper utilised the contractual ground support programme to combat stress release events, faulting, and shearing in the hard granitic rock. Ground conditions and rock support ranged from bare rock in good ground (Class I), to rock bolts, wire mesh, and channel straps, as well as steel sets every 760mm in Class V poor rock. Continuous water inflows of 30 to 35 litres per second, well below limits, were effectively contained in both tunnels.
On October 14 this year, after 30 months of combined excavation (and just over a year from the project re-start) the first Robbins machine completed its excavation in the raw water tunnel, ahead of the revised schedule. The second Robbins TBM holed through at an angle into the raw water tunnel, in order to hollow out an initial cavity for excavation of a chamber. As of November the chamber was being excavated as a site to conduct raise drilling of the 270m deep Capilano shaft.
“We are quite pleased with the breakthrough. The success of this project can be attributed to having an excellent crew of knowledgeable people, good preplanning of the work and very good TBMs,” says Frontier-Kemper project manager, Serge Moalli.
Capilano shaft construction utilising a raise borer will begin with a pilot-hole drill capable of vertical accuracy to within 0.2 per cent. After removal of the TBMs raisebore reamers will be brought through the tunnels and attached to the drill string to excavate two 4m diameter shafts. Three metre diameter steel pipe will be grouted into the raisebored shafts, and then connected to the steel lined tunnel by cross structures. Frontier-Kemper estimates that the shaft construction, combined with final shotcrete and steel lining in the tunnels, will take about two years.
New Canadian expertise
The 13-person crew operated the TBMs 20 hours per day, five days per week, installing continuous wire mesh and 1.5mlong rock bolts up to the second machine’s breakthrough. A four-hour maintenance shift was part of the daily schedule, along with regular inspection of the cutterhead and disc cutters. “We chose to continue with Robbins disc cutters… they worked well for us, and we are happy with the production of up to 110m in one week,” says Boutelle.
Much of the crew from Bilfinger Berger was retained, with a significant portion having worked on another TBM project in the region.
“We have a very experienced crew here. A lot of these people worked at the Ashlu Creek project in Vancouver, and so they know how to react to the rock and work with the machine.” says JT Thorn, for Frontier-Kemper. The 4.4km long Ashlu Creek hydroelectric tunnel was bored in 2009 through broken and faulted rock up to 300MPa UCS.
“One of the most interesting results of this project is that we have created a new type of expertise in British Columbia. There is not a lot of TBM tunneling experience here in BC, but we’ve trained and developed a good work force. We are generating more interest in TBMs now that people can see the success of this project,” says Moalli.
The completion of the project is one of several examples of TBM tunneling in British Columbia, with the vast majority of hard rock tunneling being done using traditional drill and blast. “I think we’ve proven here that you can tunnel through the hard granitic rock of British Columbia, even with all its quirks and stress releases. We’ve shown that this is an effective alternative to drill and blast,” says Moalli.
Spoil is removed from the 185m deep Seymour shaft using a special portal crane The second of two Robbins Main Beam TBMs finished boring on 4 November 2010 The two Robbins TBMs began excavation of twin 7.1km-long tunnels from a common launch chamber The experienced Seymour Capiliano Partnership crew advanced the two Robbins TBM at daily rates of up to 29m, hear maintaining the machine Ground support in the granitic and metavolcanic rock ranged from none in good round to rock bolts, wire mesh, steel sets, and channel straps in poor rock The Seymour Capliliano Partnership crew celebrate the completion of tunnelling with two Robbins TBMs after 30 months of excavation
