A refurbished 6.4m diameter Hitachi EPBM records the third of sixth scheduled breakthroughs for excavation of the Northgate LRT link in Seattle.
On Friday (November 6) TBM Brenda bored through the headwall at what will be U-District Station, having already completed her first drive from the launch site at the Maple Leaf portal just south of Northgate Station, through to Roosevelt Station, in May (2015).
A second refurbished Robbins EPBM (TBM Pamela), which launched in November last year and completed first breakthrough into Roosevelt Station in July (2015), is expected to complete the parallel drive early next year (2016).
Sound Transit’s tunneling contractor JMC Northlink LLC, the joint venture partnership of Jay Dee/Collucio/Michels, will now perform routine maintenance on the Hitachi EPBM before relaunching for the final drive to complete an underground connection with the University Link at University of Washington Station. The U-Link is expected to open for service in the first quarter of next year (2016), having completed TBM excavations in 2012.
Excavation of the twin running 5.5km tunnels of the Northgate Link are on schedule for completion by the third quarter of next year (2016). E&M, fitout and cross-passage construction are scheduled for completion by the first quarter of 2018, with LRT services starting in 2021.
“TBM Brenda has now excavated 200,000 tonne of dirt to reach the U-District Station,” said Sound Transit Board Chair and King County Executive Dow Constantine. “Three tunnel segments are done; three more to go to reach Husky Stadium.”
The $1.9 billion Northgate Link Extension will connect the University of Washington Station at Husky Stadium to underground stations in the U District and Roosevelt neighborhood, and to an elevated station at Northgate. The total 7km extension from Northgate will provide 14-minute rides to downtown, seven-minute rides to Husky Stadium, and 47-minute rides to Sea-Tac Airport. Riders from Roosevelt Station will reach the airport in 44 minutes.
The second refurbished machine for Sound Transit’s Northgate Link in Seattle is in the ground following Robbins Onsite First Time Assembly (OFTA).
The 6.65m diameter Robbins EPBM, shipped in from a previous job through mixed ground for Singapore’s Downtown Line, joins another refurbished EPBM manufactured by Hitachi Zosen that was launched southwards in June 2014 from the same Northeast 94th Street portal near what will be the line’s northern terminus at Northgate Station.
The US$440.3 million design-build contract for 5.5km of twin running tunnels through a geology of glacial till and sand, and cut-and-cover construction of intermediate stations at Roosevelt and Brooklyn (University District), is held by the JCM Northlink JV of JayDee/Collucio/Michaels. The same JV was involved in construction of the all-underground University Link that the Northgate Link extends northwards from the University of Washington.
JCM is confident that refurbished TBMs are the best solution given a tight project schedule that is scheduled to see LRT trains running by 2021. Designed for use on multiple tunnels in mixed ground, the Robbins EPBM features a steel frame that is 30% heavier than other similar machines on the market, with components intended for 10,000 hours of workable life.
“Ten years ago, EPB tunneling in mixed ground below the water table was not that common; it would have been considered a big risk to use a refurbished machine,” said Glen Frank, Project Manager for JCM Northgate Link. “Now, many EPBs have been specified to deal with more challenging conditions, so there are a quite a lot more out there to be refurbished. This solution increases our ability to get a TBM to launch sooner, and is also more cost-effective.”
Robbins continuous conveyors are running behind both TBMs. “We’ve had great success with Robbins conveyors on past projects,” said Frank. “Without the conveyor, we couldn’t do this job. They cut down on costs and vibration, and allow us to use rubber-tired vehicles, rather than trains, for transport in the tunnels.”
The Hitachi Zosen machine, which was already owned by the JCM JV and used as one of four machines for construction of the now-completed University Link, is approximately 60% of the way towards its scheduled maintenance stop at Roosevelt Station.