Temporary tunnel access ramp helps Seattle Tunnel Partners rearrange work

This week, crews working for Seattle Tunnel Partners inside the bored tunnel finished building the 400-foot-long ramp shown below. You might be wondering: Why is the ramp necessary? After all, crews completed more than a thousand feet of the tunnel without one. Turns out the ramp is part of STP’s plan to complete work now – while the SR 99 tunneling machine is being repaired – that was originally scheduled to be done after tunneling was complete. 

SR 99 tunnel ramp
Looking north at the new access ramp inside the bored tunnel.

That includes transforming the launch pit immediately south of the bored tunnel. As you can see in the photos below, STP has built up from the bottom of the launch pit to the level of the future northbound roadway. This enables crews to connect tunnel systems such as ventilation and electricity to the operations building under construction at the south portal. But it left an eight-foot drop between the level of the northbound roadway and the bottom of the bored tunnel.
South portal in 2014     South portal in 2015
The south tunnel entrance in September 2014 (left) compared to the entrance in June 2015 (right).             
The temporary ramp bridges that gap and its 400-foot length makes for a gentle slope – something that will keep construction rolling now and after mining resumes. 
SR 99 tunnel ramp looking south

A view of the ramp looking south toward the bored tunnel entrance.