Building the highway inside the tunnel

Seattle Tunnel Partners is performing routine maintenance on Bertha, but important work is ongoing inside the tunnel. As the video below illustrates, a massive highway-building operation is trailing not far behind the tunneling machine.
This is no ordinary highway project. It requires a complex choreography to complete this work even as crews mine beneath Seattle. Check out the video to learn how it works.
 
 
 
 
Highway construction progress
Construction of the highway occurs in 54-foot sections. Crews build each section in stages, as shown in the graphic below.
 
Highway construction steps
 
Multiple sections of the highway are under construction at any given time. Wall foundations, for example, have been built through most of the tunnel, but the southbound roadway deck has been completed to approximately South Jackson Street. 
 
Building the highway in this fashion allows concrete the time it needs to strengthen before additional components of the highway are added at a given section. It also allows workers to spread out and complete the portion they’re working on more quickly than would be possible if all crews were focused on the same area at the same time. 
 
The graphic below shows how much highway work has been completed so far. Some of these components can’t be built until after tunneling is completed.
 
Highway construction progress
This image shows highway construction progress as of July 13, 2016.
 
We'll continue to provide updates on highway construction as STP's work progresses.