Paula and Shani Wallis, TunnelTalk
- When Hitachi Zosen was selected this week from among four manufacturing proposals to build the giant machine for the Alaskan Way viaduct replacement tunnel project in Seattle, a spokesperson at the company in Japan said they were very pleased. "The competition was very strong. One of the competing teams has a manufacturing capacity in Seattle and another has great experience in building such big machines."
- The spokesperson went on to say that the letter of intent was still to be converted to an official order but that details of a larger-than-specified 58ft (17.6m) diameter machine needed by the client can now begin ahead of manufacture at Hitachi’s Sakai works near Osaka on Japan’s main island, Honshu.
- Minimal design-build specifications for construction of the 9,100ft (2.7km) bored tunnel replacement of the viaduct called for a single closed-faced EPB or slurry TBM of at least 54ft (16.5m) diameter to accommodate four lanes on a double deck carriageway. In addition to two 11ft-wide traffic lanes, each deck needed a 6ft shoulder lane, a 2ft walkway on each deck, and a height clearance of 15ft above the main traffic lanes to accommodate all types of traffic including heavy freight trucks.
An EPBM of colossal size will excavate
the double-deck tunnel
- A closed-face, pressurized TBM is essential for driving beneath the streets of the city and through Seattle's complex geology of mixed glacial deposits of sand, gravel, tills and clays, and ungraded fill materials, all of which host a high groundwater-table. With a cover of up to 200ft (60m), maximum hydrostatic pressure at tunnel invert is expected to be 5 bar, with a potential 1.5 bar pressure difference across the face of the giant TBM from crown to invert.
- Speaking about this week's announcement, Seattle Tunnel Partners' (STP) Deputy Project Executive Chris Dixon told TunnelTalk the Japanese supplier put a very strong case over concerning its ability to meet two important technical requirements for the TBM, in particular:
• the ability to eliminate hyperbaric interventions and,
• the addition of an axial displacement of the giant 17.6m cutterhead.
Chris Dixon of Dragados/Tutor Perini speaks of the technical procurement of the huge machine
- Dixon said: "We saw the elimination of hyperbaric interventions as a big risk reduction. Obviously the ability to change the cutting tools on the cutterhead at atmospheric pressure is quicker and safer. You have to stop the machine a lot longer to do a hyperbaric intervention."
- The design-build team of Dragados-USA and Tutor-Perini of California with designer HNTB Corp, included 1,440 hours of interventions in its bid proposal. According to Dixon there is a fund in the contract to cover additional interventions, with a financial incentive attached.
- He explained: "To the extent the fund is not used, we split that with Washington State Department of Transport (WSDOT) on a 75/25 basis, where we get 75% and WSDOT gets 25%. So there is an incentive for us to minimize the hours of interventions from a financial standpoint, but also just from a safety and production standpoint."
- The other key requirement was an axial displacement on the cutterhead, which could be pushed out ahead of the shield and brought back, thereby creating a space between the cutterhead and the excavated face. This would provide space for workers to complete visual inspections of the cutterhead and cutting tools.
- "There were a variety of other technical requirements that all the manufacturers met in one way or the other, but not all of them could provide those two key requirements, both of which Hitachi Zosen was able to," said Dixon.
- Another area where the Hitachi bid scored highly was the company's ability to ship the TBM in either large or small components, with the largest piece weighing somewhere in excess of 3,000 tons, a very big piece of equipment to load and unload off a ship and transport to the site. "Hitachi Zosen has done a lot of research on how that can be accomplished," said Dixon. "We have been looking at it ourselves and we are not sure that that can be done yet, but we always have the smaller block option to fall back on, which is do-able. But the large block option would mean less disassembly of the machine for shipment from the Hitachi factory in Japan and faster assembly once on site which would save us two months on the schedule."
The new machine will be larger by several meters than the 13.6m Hitachi EPBM built recently for the Shinagawa Ohi Highway Tunnel
Largest EPBM to date
For Hitachi Zosen the new order will be the world's largest EPBM to date and the largest machine it has built, surpassing the 14.14m slurry machine it manufactured for the Trans-Tokyo Bay Highway in 1994 and the 13.6m diameter EPBM delivered recently for the Central Circular Shinagawa Ohi Highway Tunnel.
- One of the largest components of the machine would be the main bearing drive unit. Rothe Erde, one of the world's leading bearing manufacturers, explained that large TBMs require bearings of about 9m diameter. These days such large bearings can be manufactured in segments to comply with transportation limitations. One of the largest bearings produced by the company was in the 1990s when an 18m diameter unit was supplied for horizontal installation at the base of a crane. Large bearings for TBMs stand vertically and are of high precision engineering.
- As well as the TBM, Hitachi will also supply the trailing gear and conveyor systems for muck haulage. The total length of the machine will be about 326ft (99m), including cutterhead, shield, and trailing gear.
In addition to meeting the technical requirements, Dixon said the Japanese supplier was very responsive during numerous discussions in the proposal evaluation phase, and showed a strong commitment to providing what the contractor was looking for. Hitachi Zosen was also fairly creative and accommodating in structuring the payment, he said.
- "They were very enthusiastic and very sincere in their approach," said Dixon. "They have committed to payment terms associated with completing the first 20 strokes, which is about 130ft of tunneling, and then another payment tied to completion of the first 200 strokes, which is the first 1,300ft of tunneling and it is at that time that we more or less take possession of the machine.
- "The amount of support that they are able to provide, from the assembly and training of our personnel, to testing, commissioning and startup, was also very good. So aside from the technical features and delivery, we just got a sense that they were a team that would be really good to work with. Not that the other teams would not have been, but Hitachi Zosen went the extra mile to develop a relationship with us."
- The letter of intent issued by STP this week is essentially a gentlemen's agreement to work together towards executing a supply contract after the contract's second Notice to Proceed is granted by WSDOT.
- Linea Laird, Alaskan Way Viaduct Director of North and Central, said the schedule is moving forward. The final environmental impact statement was published on July 15, 2011 and is in its 30-day comment period, with a Record of Decision from the Federal Highway Administration likely to follow.
- "We still have rights of ways to deal with, and utilities to relocate, before tunnel construction, but securing the Record of Decision and issuing Second Notice to Proceed are major milestones and we anticipate they will be achieved by the end of August," said Laird.
- STP anticipates the 58ft (17.6m) diameter EPBM will take 14 months to build. A month for test runs and factory inspection will be followed by six to ten weeks for disassembly and packing (depending on whether the TBM is broken into large or small components). Another month of ocean transportation and a further six to ten weeks to assemble the machine on site would see an excavation start date of April or June 2013.
Japanese machine for Alaskan Way mega drive - TunnelTalk, July 2011
Alaskan Way mega-project procurement - TunnelTalk, Oct 2010
Best value proposal for Alaskan Way - TunnelTalk, Dec 2010
Final EIS supports Alaskan Way tunnel - TunnelTalk, July 2011
Tracking the world's mega TBMs - TunnelTalk, July 2011
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