Alaskan Way repair pit excavation begins

6 November 2014

USA - Contractor Seattle Tunnel Partners (STP) has begun digging the circular pit crews will use to access and repair Bertha, the 17.5m-diameter SR 99 tunnelling machine.

On 17 October, an excavator rolled into position to the west of the Alaskan Way Viaduct near Pier 48, where STP stopped tunnelling last December after Bertha overheated. There, crews began taking the first scoops of soil from what will become a 120ft-deep, 80ft-wide pile-supported pit.

Approximately 20,000cu.yd (15,300cu.m) of soil will be removed from the pit over the course of excavation. Because a number of other important construction activities are competing for space near the pit, there will be many days when excavation doesn't occur. Contaminated soil will be hauled by truck or barge to a disposal facility; STP will store non-contaminated soil and use it to fill in the pit after tunneling resumes.

Meanwhile, crews are continuing to lower groundwater in enclosed areas near the machine and prepare for installation of the massive crane that will be used to hoist pieces of the machine to the surface for repair later this autumn.