The Big Bertha saga on the Seattle SR99 Viaduct Replacement project has come to an end as the 57.5-foot diameter tunnel boring machine (TBM) broke through the final three feet. Check out these videos of the breakthrough taken by drone. And if you haven't seen a TBM in action, this gives you an idea of the pace and power and it eats its way through concrete and rebar.
The tunnel with have two decks, each deck carrying two 11-foot lanes with an eight-foot safety shoulder and a two-foot shoulder in each direction. To learn more about Big Bertha or the history of the project, check out the WSDOT SR99 website here.