Paula Wallis, TunnelTalk
- A tough, high stakes decision paid off with final breakthrough coming ahead of schedule to complete the 13-mile (20.9km) Brightwater Conveyance Tunnel in Seattle.
- The Lovat EPBM or BT-3c machine made its final pushed through a concrete plug and into the shell of the stranded TBM Tuesday August 16, some 50 days ahead of schedule (Fig 1).
- "It just feels really good to see the excavation come to an end, almost four years after the first of four TBMs went into the ground," said Judy Cochran, Project Manager for the owner King County. Cochran was in the tunnel for the breakthrough along with about 20 members of the construction team. "It was the people that have directly built this tunnel and we've all worked together very closely so it was great to be there and see it happen," she said.
- The hole through came 300ft (91.4m) below Lake Forest Park at 2.26pm. Greg Hauser, Project Manager for the contractor, Jay Dee/Caluccio JV (JDC) said, overall the drive went better than anticipated. "We expected a lot of problems because we were mining downhill. We had a lot of precautionary measures as far as duplication of pumps and power, and a call out notice if we started to get water in the heading, because water in the heading was one thing that would have put us out of business. We also had procedures for bringing the loaded muck cars uphill. We had dual locomotives and we didn't know what that would do to our schedule. We did a lot of planning for what-ifs and as it turned out none of the alternate planning was necessary. The job went very well for us," he said.
- JDC signed a contract in April 2010 to finish the remaining 1.9 miles (3km) of the four-mile (6.4km) BT-3 tunnel after the heading for the original contractor, Vinci/Parsons/Frontier-Kemper JV (VPFK) ran into trouble. In mid-2009, the JV's slurry TBM suffered major damage and required time-consuming repair. King County Executive, Dow Constantine, made a decision to hire JDC - which had completed the adjoining four-mile BT-4 tunnel and had its EPBM machine in place - to continue the BT-3c drive west.
Lovat TBM Elizabeth breaks through into the shell of stranded TBM to complete the 13-mile tunnel
- The plan was to drive the 15.5ft (4.7m) o.d. BT-3c machine into the skin of the 17ft (5m) diameter slurry machine. Ahead of that VPFK had to gut their machine, removing the bulkhead and cutterhead. This required a complicated ground freezing operation that included a freeze pattern of about 35 holes, +300ft (about 100m) deep to freeze the ground immediately around and in front of the TBM. SoilFreeze did the design work and the freezing operation and DBM Contractors did the drilling. The freeze down began in March 2011 and by the middle of June VPFK was removing the bulkheads and the cutterhead. By mid July the BT-3c machine was 100ft (30.4m) away and parked, while the contractor installed a 14ft (4.2m) long concrete plug inside the shield of the gutted TBM for the waiting TBM to bore into.
Fig 1. The four TBMs that built the Brightwater Conveyance Tunnel
- "Overall the drive went very well, said Cochran. "Their overall production average was higher than we expected. We planned for 50ft (15.2m) per day and 250ft (76.2m) a week and allowed in the schedule 30 days of interventions, which they used. All of the maintenance on the cutterhead was done in free air and the most significant repair came in May 2011 when the cutterhead was damaged by a boulder and took about a month to repair. But even so, the contractor came in ahead of schedule."
- "We had a terrific crew," said Hauser, "and if anybody deserves credit for our successful operation it is our Superintendent Tom McMahon. He is a tremendous tunneller and a tremendous superintendent. It was he who ran all the crews and made everything happen. VPFK were also present for the hole through and were very helpful in assisting us."
- Construction on the two central BT-2 and BT-3 tunnels in opposite directions from the North Kenmore shaft by VPFK was suspended in May 2009 after inspections revealed extensive damage to the cutterhead rims on the two 17ft (5m) diameter Herrenknecht Mixshields. VPFK successfully repaired the BT-2 machine and tunneling resumed mid-Feb 2010 and was completed in June 2010. However BT-3 never recovered.
County staff and contractors eagerly await the arrival of Elizabeth
- Cochran said there was never any question that VPFK could make the repairs to the TB-3 machine and finish the job. "The issue was over how it planned to complete the remaining work," she said. "They planned to create artificial safe havens for the remainder of the drive and we were looking at some very long delays in order to get the real estate, the property rights and to design and implement these artificial safe havens to conduct the TBM maintenance."
- On top of that VPFK estimated the remaining 10,000ft (3,048m) of excavation would be finished in December of 2012, which was unacceptable, said Cochran.
- "There is also a difference of opinion as to the cause of the damage to the cutterhead rims. We think that some of VPFK's operation of both BT-2 and BT-3 shows they were mining with clogging in the cutterhead and we think that could have been the cause. Also on BT-2, some of the time they were mining with the gauge cutter worn down to a point where there was no over-cut. The answer we got back from the contractor is that, on a slurry machine, the over-cut doesn't really matter," she said.
- King County is currently in litigation with contractor VPFK regarding $206 million in disputed costs. A trial date has been set for September 2012. Meantime VPFK remains under contract to complete the final tunnel liner in the BT-3 tunnel and to restore the Kenmore property that served as a staging area and access portal during tunnel construction.
- With hole through of the BT-3c machine JDC will now grout the two machines together then gut and remove all the components of its machine back through almost six miles (9.65km) of tunnel. "We will shotcrete the closure between the two tunnel sections and back out from that closure to the Ballinger Way Portal to complete the BT-3 tunnel," said Hauser.
Elizabeth completes 5.9 miles of tunneling
- Because the two tunnels are different diameters, DJC, as part of the BT-3 completion contract, had to order new liner segments, while VPFK was directed to dispose of 10,000ft (3,048m) of tunnel segments manufactured for its TBM.
- Despite the setbacks King County says the $1.8 billion Brightwater project is currently within 3.3% of its original baseline budget established in 2004, when accounting for 5% inflation.
- According to the most recent cost trend report issued in January, the County expects to complete the $964 million Brightwater conveyance tunnel for about $141 million less than the baseline budget established in 2004.
- With excavation now complete the big push is to get flows in the tunnel. This is scheduled to start in September 2012 with the entire tunnel system in service by June 2013.
Brightwater action to limit costly delays - TunnelTalk, Feb 2010
Dewatering assists Brightwater TBM repairs - TunnelTalk, Oct 2009
Brightwater TBMs in trouble - TunnelTalk, Mar 2009
Brightwater update - TunnelTalk, Jan 2009
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