Big Bertha arrives for tunnel dig under Seattle



Posted on April 3, 2013 at 9:33 AM

SEATTLE - A vessel now riding at anchor in Elliott Bay has the words “jumbo shipping” painted on the sides. It’s no joke.  On its deck sits what the Washington State Department of Transportation claims is the world’s largest tunnel boring machine.

The machine, named “Bertha,” has a rotating head 57 ½ feet across. Broken down, its 41 pieces will be unloaded in a few days and will proceed to a pit where it will be re-assembled and begin a nearly two-mile long journey under downtown Seattle.

And while construction of a pit near the downtown Seattle stadiums has been under way for over a year, the tunneling is the major part of the job, and the time when the business of Seattle’s tunnel gets serious.

A February 27th report released by an independent expert review panel warns that “...the commencement of tunneling will present important challenges that may impact schedule and budget...”

Already, the schedule is a bit off.  WSDOT says the boring machine, roughly the size of a large state ferry with an overall length of 300 feet, had a drive problem delaying its departure from Osaka, Japan to Seattle. That delay was about two weeks.

But the pit that will receive it is also a bit delayed.

“We have another three to four weeks left on the pit,” said Matt Preedy, the tunnel project’s deputy program administrator.

Preedy says such delays aren’t unexpected.

“There was always a little bit of float for when we started the tunneling itself,” said Preedy.

Instead of beginning the dig in June, Preedy says it’s looking more like July.

But he is anticipating the tunnel to open to traffic on schedule in December of 2015, sounding less hopeful about getting the tunnel open ahead of schedule in October or November of that year.

The contractor is more optimistic.  Project manager Chris Dixon of Seattle Tunnel Partners, the consortium of international and local companies assembled to actually build the tunnel, thinks the tunnel could be open earlier in December of 2015. 

“If we do realize some slippage,” said Dixon, referring to the construction schedule. “We develop recovery plans that allow us to get back on schedule.”

An early opening means more money for the contractor, a late opening a money loser, as the contract is for a fixed price.

Dixon says tunnel construction is really multiple jobs at once. As Bertha digs and sets concrete tunnel liners to maintain the structure, actual construction of the double deck highway will begin behind it, all the while allowing conveyors to remove dirt while providing ventilation to the crew which will be heading deeper and deeper downtown.

At the north end of what is now the Battery Street tunnel, construction is already proceeding to dig a second pit, the place where Bertha will break through in 2014.