The hulking cutter is the first large piece of the $80 million tunneling machine, named "Bertha," to be unloaded since it was brought 5,000 miles by ship to Seattle from Japan.
Moving at a slug-like pace of 2 mph, the cutter was carried aboard a special transporter from Pier 46 toward a deep pit where it will be lowered and begin tunneling this summer.
Other parts of the tunneling machine will be offloaded in the coming weeks. They will be assembled together at the 80-foot-deep tunneling site - a process that is expected take two to three months.
The pieces are arranged strategically on the ship, so that crews can move them to predetermined storage locations within the work zone as they are unloaded.
In addition to building the launch pit, crews in Seattle are preparing the surrounding area for tunneling. That includes strengthening the soil and building protected underground work areas along the initial section of the tunnel route so crews can perform scheduled inspections of the machine before it begins tunneling beneath the city.
Work is also under way near the north end of the Battery Street Tunnel to prepare the area where Bertha will emerge at the end of tunneling.
The Highway 99 tunnel is expected to be completed by 2015, clearing the way for the removal of the Alaskan Way Viaduct in 2016.