Seattle Tunnel Partners got the green light to resume digging Tuesday night in front of Bertha, the stranded boring machine for the Highway 99 tunnel project.
The state ordered the contractors late Friday to stop excavating an access vault, and write an emergency plan that would allow them to safely stop groundwater pumping — in the event Pioneer Square soil sank beyond the 1 inch measured last month. Groundwater pumping, which is continuing, is suspected of causing the soil and Alaskan Way Viaduct to settle, and risking damage to city water pipes. No new settlement has occurred, the state says.
That emergency plan was reviewed and approved Monday afternoon by the Washington State Department of Transportation, the agency announced early Tuesday afternoon. The leading option would be to pour dirt into the vault, where its weight would prevent groundwater pressure from blowing upward into the pit.
Seattle Tunnel Partners has dug 84 feet of the 120-foot-deep access pit, where eventually, Bertha’s damaged front-end parts are expected to be hoisted to the surface for repairs.