Construction for Alaskan Way shaft walls off schedule1 August 2014
USA - Seattle Tunnel Partners (STP) announced on July 28 that building the underground walls of the circular pit creating access to repair the TBM will take longer than anticipated, according to the Washington Department of Transportation (WSDOT).
The work on the walls will continue through August, and while this date is later than anticipated, STP said that tunneling is still expected to resume as scheduled in March 2015.
Crews are building a self-supporting, concrete ring that is 120ft deep and 80ft wide in difficult ground conditions. 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 anticipated," WSDOT said. "One factor is the addition of 11 piles to the pit's design, bringing the total number of piles to approximately 84. Crews are also 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."
Other work as part of the repair plan has stayed on schedule. The new main bearing has arrived in Seattle and will be assembled closer to the time it's needed, likely this fall. Manufacturing 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. Cranes are being assembled the next two months to lift the larger pieces of equipment into the shaft.