Seattle University Link Light Rail U220

Contract U220


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


Joint Venture Traylor Frontier
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


Start of construction


End of construction


Project total value

approx. 0.3 million €


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)