Follow Bertha

Seattle Tunnel Partners working to repair Bertha

In summer 2013, Bertha, the world’s largest tunneling machine, began digging the SR 99 tunnel beneath downtown Seattle. In December 2013, Seattle Tunnel Partners, the contracting team hired to design and build the tunnel, stopped excavation approximately 1,000 feet into the dig after measuring increased temperatures in the tunneling machine. While investigating the cause of the high temperatures, STP discovered damage to the machine’s seal system and contamination within the main bearing. STP and manufacturer Hitachi Zosen are currently repairing and enhancing the machine.

Bertha returning to the access pit

On Aug. 25, 2015, after repairing and enhancing the machine at the surface, Seattle Tunnel Partners and crane crews from Mammoet successfully lowered the machine's 2,000-ton front end to a platform at the bottom of the access pit. Crews are now connecting the piece to the portion of the machine that remains in the ground. Three additional pieces will be lowered into the 120-foot-deep pit in the coming days. Below are links that illustrate STP's plan to resume tunneling. The latest schedule is available here.

Live view of construction

Construction is hard to see in person because crews built a wall to shield neighbors from construction noise. The best view of STP’s work is from our time-lapse camera. Click on the "SR 99 tunnel access pit" camera in the grid below to watch crews as they work to access and repair Bertha, or check out other viaduct-related construction happening elsewhere along the SR 99 corridor.