To consolidate, disseminate, and gather information concerning the 710 expansion into our San Rafael neighborhood and into our surrounding neighborhoods. If you have an item that you would like posted on this blog, please e-mail the item to Peggy Drouet at pdrouet@earthlink.net

Saturday, December 21, 2013

What's blocking Bertha? Answers elude engineers


By Lindsay Cohen, December 20, 2013

  What's blocking Bertha? Answers elude engineers »Play Video

"Bertha," the massive tunnel boring machine, is drilling a two-mile tunnel to replace the 60-year-old Alaskan Way Viaduct.

SEATTLE -- Want to know what's blocking Bertha? Grab a New Year's party favor - and wait.

State transportation officials said Friday it will likely be several more weeks before they know what's in the way of the world's largest tunnel boring machine, which ground to a halt Dec. 6 after hitting something.

"The contractor can create a space in front of the cutting head and the ground - through proper means - and then the workers would be able to look in front of the cutting head," said Matt Preedy, deputy program administrator for the Alaskan Way Viaduct Replacement Program.

Crews are in the process of building 10 wells which will help alleviate pressure in the space in front of Bertha. Once the wells are complete and operational - likely the end of next week - workers will be able to inspect the space in front of the machine.

One of the ways to get to that spot involves going through a manlock, or a passageway between spaces of different air pressure. There are manlocks at the front of Bertha's bulkhead, Preedy said, which would allow workers to see what is stopping the 7,000 ton machine.

With no swift answer to what's blocking Bertha, speculation continued Friday as to what might be in her path.

"I really do hope it's something in a way unnatural because it's a more fun story that way," joked David B. Williams, a geologist and author who has studied the topography of Seattle.

Williams points out that the first settlers to the Emerald City used anything they could find - sawdust, timber, even garbage - to fill in the land around Elliott Bay.

"Anywhere you go in Pioneer Square, you're basically on 'made' land. You find old shoes, newspapers; there's a boat buried in downtown. So you name it - it could be down there," Williams said.

Historic records show that a boat called The Windward ran aground on Whidbey Island and was towed into downtown Seattle, Williams said. The ship eventually became part of the landfill beneath city streets.

"As the city grew, they just covered up that boat and it's still there to this day," Williams said. "We don't know exactly where it is because they haven't found it. We think it's probably in an intersection somewhere."

For now, Bertha remains stuck about 60 feet below South Jackson and South Main streets. The tunnel contractor said it's too early to say if the blockage will impact the overall cost of the project or the projected completion date, but that engineers are looking at what other work can be done while Bertha takes a break.

"The only real option is to remove (the object) and hopefully we can do that with mechanical means," said Chris Dixon, project director for Seattle Tunnel Partners. "You can't really change the route. You can't back the machine up because you have the segmental lining behind you, so all you can really do is proceed forward."