Now just getting to Bertha in order to fix the stalled tunnel-boring machine under downtown Seattle is taking longer than anticipated.
Bertha hasn’t had substantial movement since December 2013 and an access pit needed to reach the front of the underground machine to fix it ran into challenges, pushing the construction of the pit through August, later than scheduled.
Repairs to Bertha, though, are still expected to have North America’s largest TBM boring again in March 2015.
Crews from Seattle Tunnel Partners say building a self-supporting, concrete ring pit 120 ft deep and 80 ft wide is no easy task, especially with the difficult ground conditions near South Jackson Street just blocks from Seattle’s stadium district and near the waterfront.
Well more than half the underground piles are in, with roughly 30 more to go. Part of the delay comes from the need to add 11 piles to the pit’s design, bringing the total number to 84. The large interlocking piles, necessary so the pit can support itself without tiebacks or other reinforcements, also take time to install.
The Washington State Dept. of Transportation says plenty of other work continues related to the project that hopes to fix Bertha and have the machine back to boring a 1.7-mile-long tunnel beneath Seattle as part of a replacement to the Alaskan Way Viaduct. Those projects include:
• A new bearing has made its way to Seattle and will likely get assembled this fall, closer to when it will get installed.
• A new outer seal ring, a thrust seal ring and bearing block are all still under construction. Once finished and inspected, they will get shipped from Japan where TBM maker Hitachi Zosen is based to Seattle.
• Crews will assemble a 300-ton crawler crane in order to assemble a 600-ton crawler crane, likely starting in September.
• The 600-ton crawler crane will help assemble a modular lift tower that will lift the largest repair pieces into the access pit.
• The 2,000-ton lift tower construction started in July and will continue through the fall. Pieces of the red lift tower continue to arrive in Seattle.
Tim Newcomb is Engineering News-Record’s Pacific Northwest contributor. He also writes for Popular Mechanics, Sports Illustrated and more. You can follow him on Twitter at @tdnewcomb or visit his website here.