Seattle Tunnel Partners (STP) is taking longer than expected to build the underground walls of the circular pit crews will use to access and repair the S.R. 99 tunneling machine, but tunneling is still expected to resume as scheduled in March 2015, according to the Washington State Department of Transportation (WSDOT).
Building a self-supporting, concrete ring that is 120 ft deep and 80 ft wide is no easy task, especially given the difficult ground conditions near South Jackson Street, according to WSDOT. STP crews have completed more than half of the underground piles and are working around-the-clock, seven days a week to complete the approximately 31 remaining piles.
There are several reasons the work is taking longer than expected. One factor is the addition of 11 piles to the pit’s design, bringing the total number of piles to approximately 84. Crews also are working with exceptionally large, interlocking piles, which are necessary to make the pit self-supporting without tiebacks or other reinforcements. A self-supporting pit is what will allow the tunneling machine to mine through its walls, but the large piles take longer to install than standard piles.
While pile work continues, crews are making progress on other areas of the repair plan on schedule, including:
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• Shipping repair pieces: The new main bearing has arrived in Seattle and will be assembled closer to the time it is needed, likely this fall;
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• Manufacturing repair pieces: Other repair pieces, such as the new outer seal ring, the thrust seal ring and bearing block are nearing completion. After these pieces are fabricated and inspected, Hitachi Zosen will ship them to Seattle;
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• Assembling a 300-ton crawler crane: This crane will be used to help assemble the 600-ton crawler crane. Pieces of that crane will arrive in September, and assembly will begin shortly thereafter;
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• Assembling a 600-ton crawler crane: This crane will be used to assemble the modular lift tower (massive red crane) that will lift the largest pieces of the machine from the access pit. Parts of that crane also will arrive in September, and assembly will begin in late September; and
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• Assembling the 2,000-ton modular lift tower: Starting in late July and continuing through fall, crews will begin to stage the modular lift tower. Parts of the modular lift tower will arrive over the next several months beginning in late July.
