Jan. 8 update: crews continue drilling exploratory shafts
On Jan. 8, crews finished drilling the second of four planned exploratory shafts in front of Bertha, the SR 99 tunneling machine. The shafts are being used to further identify the limits of any metal in front of the machine and remove as much of it as possible.
If an object is encountered, crews will try to identify and remove it from the ground. If no objects are detected or removed from the shafts, the shafts will be filled to form part of an underground barrier that will create a safe environment for workers to enter the machine’s excavation chamber.
During drilling of the first shaft, crews believe they may have encountered an obstruction, but couldn’t tell for sure because the drill quickly passed by it on the way to its final depth of 118 feet. No objects were encountered during drilling of the second shaft.
The top of the machine is located about 60 feet below the surface between South Jackson and South Main streets, to the west of the State Route 99 Alaskan Way Viaduct. Wells installed near the machine last month by our contractor, Seattle Tunnel Partners, are continuing to pump water out of the ground at a steady rate. Crews have completed inspecting and cleaning out the machine’s screw conveyor, which remains fully functional.
Crews are also continuing to gather information about any other factors that might have contributed to the stoppage of tunneling last month. The overall cause of the tunneling slowdown will not be known until the investigation is completed.