Feb. 9 project update: Cradle awaits Bertha’s front end
After completing access pit excavation late last month, Seattle Tunnel Partners’ crews turned their attention to building the concrete cradle at the bottom of the pit. Over the last week, they placed several base layers, formed the cradle with rebar and poured nearly 1,000 cubic yards of concrete to complete the cradle on Sunday, Feb. 8. The cradle will support the machine after it moves through the pit’s southern wall, which is about 20 feet thick.
The next step is to tunnel through the concrete wall. The length of time it takes Bertha to reach the pit will depend largely on her ability to mine through and digest the concrete. If she’s unable to mine through the wall, STP will create an opening from within the pit to give her an unobstructed path forward. Once inside the pit, crews will prepare the machine for disassembly and use the massive red gantry crane to hoist the front end of the machine to the surface for repairs. This narrated video (links to YouTube) explains the repair process in detail.