New Irvington Tunnel bid result, San Francisco
New Irvington Tunnel bid result, San Francisco Apr 2010
Shani Wallis, TunnelTalk
At a public bid opening last week (Thursday, 1 April) the Southland/Tutor Perini JV emerged as the apparent lowest of four bidders for the 3.5 mile (5.6km) New Irvington potable water supply tunnel for the San Francisco Public Utilities Commission (SFPUC) in Northern California.
Pic 1

Fig 1. Principal elements of the WSIP improvement program

The JV's bid of $226,657,700 is set against an Engineer's Estimate of $253,202,000. The three competing bids were submitted by: Barnard Construction - $275,150,000; Kiewit/Atkinson JV - $292,499,000; and Irvington Tunnel Constructors, a JV of Obayashi/Kenny Construction/JF Shea at $293,027,421. The Engineer's Estimate was prepared by contract designers URS-Jacobs Associates.
The New Irvington contract is the third major tunnel project in SFPUC's $4.6 billion Water System Improvement Program that comprises 86 separate projects across seven counties and is designed to upgrade and secure Hetch Hetchy drinking water supply to its 2.5 million Bay Area customers (Fig 1).
At a bid price of about $64.77 million/mile, the New Irvington Tunnel is the most expensive of the three tunnel projects in the program. This is compared to the $55.7 million bid by the for the 4,200ft (3/4 mile) 12ft (3.7m) o.d. Crystal Springs Tunnel by the Shank/Balfour Beatty JV and a $43 million/mile bid by the Michels/Jay Dee/Coluccio JV late last year for the 5 mile x 108in i.d. (8km x 3m) Bay Tunnel, the first bored tunnel to be excavated under San Francisco Bay. The new Irvington Tunnel is the largest in diameter at 14ft (4.26m) o.d., and between 8.5-10.5ft (2.6-3.2m) i.d., and where the Crystal Springs Tunnel and Bay Tunnel projects are both TBM excavations, New Irvington is specified as a conventional excavation project.
"The geology along the New Irvington Tunnel alignment is complex with sections of hard rock and seven fault zones to be crossed. Squeezing, running and ravelling ground conditions and high ground water inflows are to be anticipated," said SFPUC Project Manager, David Tsztoo. For these reasons, the project was considered unsuitable for TBM excavation. "The contract allows excavation by roadheaders with sections of drill+blast through harder rock and hydraulic excavators through the fault zones," said Tsztoo.

Steel final lining where needed

Steel arches are designed on 4ft centers throughout the 3.5 mile x 14ft (4.2m) horseshoe-shaped tunnel as part of a comprehensive set of primary support elements that includes rock bolts where needed and either wet- or dry-mix shotcrete reinforced with steel- or poly-fibre. Once excavated the tunnels will be finished with a final lining of either reinforced concrete cylinder pipe (RCCP) or in-situ concrete lining to 8.5-10.5ft i.d.. A steel liner will be installed as a final lining across the faults and as needed elsewhere.
Excavation is expected to take almost 2 ½ years working from four headings - the two portals and in both directions from an intermediate shaft. The maximum cover over the tunnel is about 700ft and the intermediate working shaft at Vargas Road is about 120ft deep. Two headings, one 4,000ft (1.2km) in the westerly direction and the other 7,000ft (2.1km) easterly, will be excavated from the 40ft (12m) diameter shaft. The other 7,150ft (2.2km) heading will be excavated from the Alameda West Portal and a short 500ft (150ft) heading, limited due environmental restrictions in the residential neighbourhood, will be advanced form the Irvington portal.
Due to the topography, two of the drives for the pressurised water supply tunnel are on a down hill gradient requiring special consideration for pumping control of ground water ingress. Treatment of ground water before discharge into local waterways and protection of the local environment is a major undertaking for all the construction contracts in the overall SWIP program.

Irvington portal of the 1930s construction contract

After evaluation and confirmation of the bids, award of contract is scheduled for late May with start of construction expected in July. Depending on the means and methods proposed by the successful contractor, it is expected that three roadheaders of large size will be applied to progress the three longest drives simultaneously and on 14ft high x 14ft wide full-face rounds, although a top-heading and bench is permissible if smaller roadheaders are engaged. The fourth heading from Irvington portal will be completed within the overall 1,390 calendar day contract.
Although part of the wider Water System Improvement Program (WSIP), operation of the New Irvington Tunnel is not dependent on completion of any other part of the works. It is designed to provide 100% redundancy of the existing Irvington Tunnel built in the 1930s. The 78-year old tunnel in the hills east of Fremont, is a critical component of the 160 miles (257km) of pipelines and tunnels of the Hetch Hetchy System. When the new tunnel is completed (expected in April 2014) the existing tunnel can be shut down and inspected for the first time in more than 40 years. "The new facility provides redundancy in the event of any disruption caused by potential major earth quakes in this seismically active part of the world," said Tsztoo. "Once complete both tunnels will be able to operate either independently or together."
Before that day there is a challenging schedule of tunnelling to be completed by the New Irvington Tunnel contractor. Hatch Mott MacDonald is SFPUC's construction manager for the project.
Water tunnels to recharge aging system - TunnelTalk, Sep 2009
Crystal Springs Bypass Tunnel awarded - TunnelTalk, Oct 2008
Fierce competition creates slimmest of margins for Bay Tunnel contract - TunnelTalk, Nov 2009
New Irvington water tunnel advertised - TunnelTalk, Jan 2010
San Francisco Public Utilities Commission (SFPUC) Water System Improvement Program

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