Many neighbors living east of Beacon Hill Station received a flyer (PDF) from Sound Transit this evening, describing the current status of the “voids” discovered when digging the Beacon Hill tunnel. Last year, nine sub-surface voids were found and filled with a controlled-density fill, and the ground at the bottom of the voids was injected with grout to stabilize it.
According to the alert sent out by Sound Transit today, there are still about 400 cubic yards that need filling, but the voids aren’t large or near the surface, and Sound Transit believes that there is no imminent danger to property nearby.
Sound Transit’s next steps are to work with local property owners and their neighbors to coordinate work to fill the voids. They expect the project will take about four to six months.
A Seattle Times (BHB partners) article contains further information on the project, including a very good description of how the voids are formed.