Bertha, the giant boring machine digging the new SR-99 tunnel has been stationary for many months after breaking down finally moved ahead three feet so they can begin repairs, the Seattle Times reports,
“The giant drill’s cutter teeth now rest against the south edge of a concrete repair pit, Todd Trepanier, state Highway 99 tunnel administrator, told the Seattle City Council. Dirt will be removed from the 120-foot-deep, ring-shaped pit this month. Bertha will chew through a 20-foot thick wall into open air. Then a giant crane will lift the whole front end to street level, and take it apart. The main bearing and its rubber seals will be replaced, and steel reinforcing plates will be added. Gaps in the rotary cutting head will be enlarged, to increase the flow of excavated dirt toward the conveyor system.
The tests were meant to check Bertha’s performance and temperatures, to choose “operating parameters” for when the machine drills several more feet into the repair ring, Dixon said. Also, he said the 3-foot advance positioned the machine better for workers to add chemical grout at the back. The grout will form a barrier to block groundwater from flushing into the repair pit.”