Sinkhole Opens Above Northgate Link, Two Homes Evacuated

Approximate location of the sinkhole. Graphic via Jacobs & Associates.

A sinkhole has opened up just South of the Roosevelt Light Rail station on Sunday evening. According to a release from Sound Transit:

Crews for Sound Transit's Northgate Link light rail construction contractor are taking steps to fill a small sinkhole that emerged in front of a home on 12th Avenue Northeast near 62nd Street Northeast above tunneling that took place last year. The sinkhole, with an opening about six feet long, will be filled with cement this evening. Crews will conduct ground-boring tests in the area to assess whether there are other issues in the area above where one of the contractor's tunnel boring machines passed approximately 50 feet below last fall. Sound Transit and its contractor will be working closely with the City of Seattle on follow-up.

A sinkhole opened up on Beacon Hill in 2009, just as Central Link was opening, a year or more after tunneling had completed. Sound Transit's contractor filled the hole at a cost of $1M. The Times has a good graphic from that episode showing how sinkholes can occur when the tunnel boring machine hits sandy soil and too much fill is removed. The Beacon Hill tubes were 135 feet under the surface where the sinkhole developed.

The problem-plagued Bertha, tunneling the new Highway 99, was stopped after sinking was discovered in Pioneer Square in 2015 and on the waterfront in 2016.