Paula Wallis, Reporter

Fig 1. University-Link alignment

Contractors are lining up to bid the second of two tunneling contracts to extend Seattle’s 14-mile light rail starter line that opened last month.

The University Link (U-Link) stretches entirely underground in bored tunnels from the north end of the starter line, through an underground station at Capitol Hill and on under the shipping canal between Lake Washington and Elliot Bay to the University of Washington.

The 3.15-mile extension is broken into two contracts, U220 from the University of Washington Station to the Capitol Hill Station and U230 from the Capitol Hill Station to Pine Street Stub Tunnel (Fig 1).

Fifteen prime contractors have taken out plans and attended an industry outreach meeting in June to bid on the U230 contract that has an estimated value of $150 - $175 million (Table 1).

The fixed price, lump sum contract will be awarded to the lowest qualified bidder. A public bid opening is scheduled for August 26, 2009 at 11am Pacific Time. Sound Transit hopes that the large number of interested contractors will continue a trend of competitive bids that are beating the Engineer's estimates.

Table 1. Contenders

On June 5, 2009 Sound Transit awarded to Traylor/ Frontier-Kemper JV the U220 tunnel contract for the alignment from Capitol Hill to University of Washington. The JV's low bid of $309.2 million came in 22% or $86 million below the Engineer’s $395.35 million estimate. Likewise, in December 2008, Condon Johnson's bid for the I-5 undercrossing and construction pits contract came in 34% below the Engineer’s estimate of $29.6 million. Granite Northwest was awarded the contact for utility relocation at the University of Washington station - NRC Environmental Services is working the contract for demolition and environmental remediation to prepare for construction of the Capitol Hill underground station.

Contract U230 will be award next. The work includes construction of about 3,800ft of segmentally lined twin running tunnels between Capital Hill Station (CHS) and the Pine Street Stub Tunnel (PSST); excavation and initial support of the Capital Hill Station; five SEM (sequential excavation method) cross-passages at intervals between pressurized face TBM bored tunnels; and construction of a temporary TBM retrieval shaft at the PSST headwall and completion of the tunnel interfaces with the PSST.

Construction of the early works at the Capital Hill Station by NRC Environmental Services has started, to prepare for excavation and launch of the TBM for the North Bound tube drive to the PSST.

The Capital Hill Station box excavation and initial support includes site dewatering prior to excavation; soldier pile and lagging, and soil nail walls; tie-back anchors; struts in Denny to upport utilities; and installation of a waterproofing cast base slab.

Route of the U230 contract

The twin-bored tunnels with an internal diameter of 18.10ft, have an alignment almost entirely on a curve on a 5% grade, and minimum cover of roughly 13ft at the I-5 crossing. Tie-backs are needed in the South Bound tunnel profile as it approaches the Pine Street Stub Tunnel.

The five 13ft to 19ft long SEM cross passages are 610ft to 800ft apart and will have support categories 1 and 2.

The U230 bid submittal and bid opening is scheduled for August 26. Board approval to award is planned for October 2009 with the Notice to Proceed set for November 4, 2009.

The U-Link extension has a 6.5-year construction schedule with a projected completion date of 2016. It will add almost four miles to the 14-mile started line now in service. Evenutally 55 miles of light rail service will connect Central Puget Sound stretching from Seattle to Lynnwood, Bellevue, Redmond, Mercer Island and Federal Way by 2023.

Few bids, but trend continues for Seattle LRT - TunnelTalk, Mar 2009
Low bid cuts cost of University Link - TunnelTalk, Mar 2009
Strong competition starts North Link in Seattle - TunnelTalk, Dec 2008
Beacon Hill celebration and investigations - TunnelTalk, Jul 2009

Sound Transit: University Link Light Rail