Seattle University Link Light Rail U220

Contract U220

Client

Sound Transit, Regional Transit Authority, Seattle,
Washington, USA

Contractor

Joint Venture Traylor Frontier
Consultant:
BeMo USA Inc., Reston, VA as consultant for execution of NATM crosspassages between two segmentally lined TBM tubes; Technical Support, Know-how transfer; Senior NATM Tunnel Engineer on site

Project location

Seattle
Washington
USA

Start of construction

2011

End of construction

2012

Project total value

approx. 0.3 million €

Geology

Over-consolidated sand/clay, at some crosspassage locations more than 60 m overburden (ground water pressure 6 bar), partly additional measures necessary (spiling, vacuum dewatering, ground water lowering by means of surface wells, potentially gassy conditions)

Technical Data

• 2 TBM tubes
inner Ø 18.83 ft (5.74 m)
length 2 x 9,842.52 (2 x 3,000 m)
• Excavation and support of 16 NATM crosspassages
• Cross sections approx. 20 – 30 m² (215.28 SF – 322.92 SF)
• Deep sump in one of the crosspassages
• Execution by mini excavator (Brokk, CAT) and attachment tools (shovels, road header, chisel); partly manual excavation
• Excavation of some crosspassages concurrent with TBM excavation
• Installation of shotcrete propping system in main tunnels
• All crosspassages located underground water table
• Waterproofing
• Secondary lining (cast in situ / cast-in-place (CIP) concrete)