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00000181-fa79-da89-a38d-fb7f2a000000Bertha, the world's biggest tunneling machine, is a five-story-tall monstrosity of drilling tasked with digging out the tunnel for State Route 99 to replace the Alaskan Way Viaduct. It's journey to the center of the earth underneath downtown Seattle began in July 2013, and since then the project has seen its fair share of successes and failures.Follow the progress of the $3 billion megaproject with KUOW.

Under-promised and over-delivered: Progress on the tunnel

Progress at last on the tunnel being built to replace the Alaskan Way Viaduct.
Flickr Photo/Washington State Department of Transportation CC BY-NC-ND 2.0)
Progress at last (and a pleasant surprise) on the tunnel being built to replace the Alaskan Way Viaduct.

The Alaskan Way Viaduct is back in operation after a closure that was supposed to last two weeks, but only lasted for a week and a bit.

It’s a surprise, and not the kind we are used to from Bertha, the tunnel borer that could, then couldn’t, and now apparently can. Bertha's bearings and seals were damaged early on, forcing the Seattle Tunnel Partners to haul it to the surface for a massive repair that completed just a few months ago.

The state transportation department said during the Viaduct closure, Bertha encountered no resistance and soils remained stable. That was true even as the borer passed 15 feet below the Viaduct’s foundation. It was the closest Bertha will ever be to the old highway structure, which is being taken down because it is unstable in an earthquake.

With the worst of the danger past and not a sinkhole in sight, the state reopened the Viaduct early – though Bertha will continue to tunnel nearby. The current estimate is that Seattle Tunnel Partners will finish tunneling around February of next year.

After that long-awaited day – the project is about two years behind – there will be one more tunnel-related Viaduct closure.

That's when Bertha's tunnel will be connected to the rest of Highway 99 in an operation that could take two weeks. The tunnel is expected to be open to drivers by spring of 2018.