Hole through for Crystal Springs drive
Mar 2010
SFPUB news release
- Five months after lowering the 12ft (3.7m) diameter TBM into the access shaft, contractor Shank/Balfour Beatty JV has holed through into the reception shaft after completing the 4,200ft (1.3km) long New Crystal Springs water supply bypass tunnel in San Mateo, California. Completed ahead of schedule, the tunnel and future pipeline are a critical link to the delivery of high quality Hetch Hetchy drinking water to the 2.5 million Bay Area customers of the San Francisco Public Utilities Commission (SFPUC).
- "The tunnel and pipeline will provide redundancy to the existing Crystal Springs Bypass Pipeline built in 1969 and will ensure water delivery after a major earthquake," said Julie Labonte, Director of SFPUC's Water System Improvement Program (WSIP). The existing pipeline and soils in this area are subject to failure during high precipitation or a major earthquake.
- Shank/Balfour Beatty (S/BB) was awarded the $55.7 million contract in October last year and will now install and steel pipeline into the primary lined tunnel. Contract end date is scheduled for September next year. The JV used a 12m diameter TBM designed by Shank and fabricated by Hitachi Zosen, and installed a primary lining precast concrete segments.
- TBM driving experience
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Reception shaft breakthrough
- After carrying out some modifications at the start, TBM excavation of the tunnel is reported to have progressed well. "Average progress for the one production shift per day from 7am to 6pm, Monday to Friday, was 40ft/day with a best recorded of 83ft/day, and an average of nearly 60ft/day once into the routine," said Sarah Wilson, Project Manager for the SFPUC on site.
- Behind the TBM the contractor erected a primary lining of non-bolted, non-gasketed junk segments expanded with solder jacks in the crown. The primary lined tunnel will be fitted with an inner 96in (2.5m) diameter steel carrier pipe, backfilled in the annulus with cellular concrete and secured with contact grouting injected through ports in the steel pipe and drilled through the segments to the interface with the ground.
- During excavation, ground conditions were as unpredictable as expected. "As anticipated, the sandstone was harder to mine than the mélange matrix, and the squeezing conditions foreseen in the mélange matrix of the Franciscan Complex didn't happen quickly enough to interfere with production. Convergence was not significant enough to require additional support or remining but this could be a result of the specified TBM excavation and segmental primary lining keeping these conditions under control," said Wilson.
- As the TBM progressed, tie in works at the reception shaft were completed. As a result the TBM could not be recovered through the reception shaft. "This was planned all along," said Wilson. "The trailing back-up and the main components of the TBM were retrieved back through the completed drive, the cutterhead burned out, and the sacrificial shield left in place."
- The hole through photo of the TBM was taken from within the smaller diameter tie in pipe work at the reception shaft end. Only the central 8ft of the 12ft 2in o.d. TBM cutterhead with its 23 x 17in could be seen. Remnant of a temporary steel bulkhead is also visible in the upper right side of the smaller pipe work profile.
- With the TBM retrieved the tunnel is now prepared for installation of the inner 8ft diameter pipeline that will be welded together. This will be installed in 32ft lengths of via the 160ft deep x 32ft diameter working shaft and welded together. Contact grouting will be injected via three ports in each pipe length at the 10, 2 and 6 o'lock positions.
- The Crystal Springs tunnel lies within a residential area and although tunnelling was anticipated on a 24 hour/day, six day/week schedule with no work allowed on Sundays, the S/BB JV was able to complete the drive working only one day shift/day, five days/week with maintenance shift on Saturdays. At all times protection of the local environment was a high priority. "This is something that we were not always as aware of in the past," said Wilson. "On this contract a great deal of time and attention is spent on environmental issues. There are regulations for 24 hour noise and vibration monitoring and strict regulations for water quality control. Community outreach also kept the residents of the neighborhood aware of construction activity which is allowing work to progress cooperatively."
- The tunnel is part of the $4.6 billion program, comprising 86 separate projects across seven counties, to upgrade and improve the regional Hetch Hetchy water supply system. The full program includes long reaches of trench pipeline work and two additional major tunnels contracts.
- The 5 mile x 108in i.d. (8km x 3m) tunnel under San Francisco Bay, the first bored tunnel under the famous waterway, was awarded to the Michels/ Jay Dee/Coluccio JV late
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Primary lined bypass
- last year of $215.3 million and will be excavated using a soft ground TBM and lined with a bolted and gasketed precast concrete lining. Ground breaking on the project is scheduled for the coming weeks.
- The 3.5 mile (5.6km) New Irvington Tunnel will be excavated in multiple headings using conventional methods, including roadheaders and controlled blasting in sections of hard rock, and will be finished to about 8.5ft to 10.5ft (2.6m-3.2m) diameter. Procurement of the estimated $250 million contract has been delayed from late last year and bid opening is now schedule for today, April 1, 2010. Contract award will be scheduled for late May 2010 with construction expected to begin in July 2010 towards a final completion by April 2014.
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Ground breaking for pipeline work
- Earlier this month (March 18) SFPUB celebrated ground breaking on the first phase of a $332 million construction project to install 17 miles of new pipeline leading to the San Francisco Bay tunnel. The project is let as three separate contracts. The East Bay Pipeline through Fremont and Newark is a $61.4 million project to install a new, 7 mile x 6ft diameter (11.2km x 1.8m) welded steel water line (BDPL 5), awarded to Ranger Pipelines of San Francisco. Later this spring another $56.3 million project for a further 9 mile x 5ft diameter (14.4km x 1.5m) stretch of BDPL 5 will be awarded on the Peninsula.
- Different design engineers are working with SFPUC in different capacities. Jacobs Associates of San Francisco designed the Bay Tunnel and Jacobs Engineering will undertake its construction management. URS and Jacobs Associates designed the New Irvington Tunnel and Hatch Mott MacDonald secured the construction management contract. Arup/Brierley Associates JV designed the Crystal Springs Bypass Tunnel project and Jacobs Associates is the construction manager on site. Jacobs Associates is also overseeing construction management of the pipelaying contracts for the SFPUC.
- "With the support of our regional partners and our ratepayers, we are seismically upgrading and improving the regional water system through 17 projects on the Peninsula alone," said SFPUC Regional Project Manager Husam Masri.
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Water tunnels to recharge aging system - TunnelTalk, Sep 2009
Lowering of the Crystal Springs TBM - TunnelCast, Oct 2009
Crystal Springs Bypass Tunnel awarded - TunnelTalk, Oct 2008
Fierce competition creates slimmest of margins for Bay Tunnel contract - TunnelTalk, Nov 2009
Bay Tunnel for the SFPUC - TunnelCast, March 2008
New Irvington water tunnel advertised - TunnelTalk, Jan 2010
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