A future four-lane Highway 99 tunnel under downtown Seattle can no longer be crowned the widest single-bore tube on earth.
Russia has signed a deal for a 63-foot tunnel boring machine, according to an announcement by German supplier Herrenknecht. The Seattle machine, by Hitachi-Zosen of Japan, is to be 58 feet across when it launches from Sodo in 2013.
Both tunnels push the limits of engineering. Some transportation officials argue larger machines should actually work better, because there is more space for equipment, and for workers to repair or replace cutting tools on the face of the cylindrical drill. On the other hand, the greater soil removal requires greater vigilance to prevent voids or sinkholes from forming.
Despite the size, four teams vied to supply a machine in Seattle. Martin Herrenknecht, the charismatic founder of the German company, said a year ago that he badly wanted to supply the Highway 99 machine. He lost to Hitachi-Zosen but still has a shot at bragging rights, if his device can navigate soft soils under the Neva River, connecting two sides of St. Petersburg.
The increasing size should reassure Seattle that the industry has advanced tremendously in the last five years, according to Bruce Agnew, director of the Discovery Institute’s Cascadia Center, which prodded local officials in 2008 to consider a single-bore tunnel. “They want these major projects to work,” he said. “Because these things are cutting edge and the biggest in the world, they’re going to put their best talent on it.”
On the other hand, the Seattle tunnel contract is risky enough it requires a $500 million surety bond to guarantee completion, if a machine gets stuck. And unlike many tunnels, it runs beneath two historic districts and near modern skyscrapers, where a mistake would be catastrophic.