Bertha stops tunneling again as temperature readings spike

Bertha stops tunneling again as temperature readings spike
Tunneling crews discuss their progress as they operate Bertha, the world’s largest tunneling machine, in November 2013. (Photo courtesy: WSDOT)
SEATTLE (AP) - Seattle's massive tunneling operation is on hold yet again due to ongoing problems with the world's largest boring machine, officials said Friday.

After a seven-week stoppage, crews restarted the tunneling machine - named "Bertha" - earlier this week and did a few feet of additional movement and mining. Washington state's Department of Transportation said Friday that the machinery showed above-normal temperature readings during that work.

Those same above-normal temperature readings were occurring when crews decided to stop mining in early December.

State transportation officials said in a statement they will be working with outside tunneling experts to review the situation and determine the best path forward.

"Although their investigations to date have provided a great deal of information, we will not be able to definitively identify the issue or issues facing the machine until tunneling experts complete their review," the Transportation Department said in its statement.

The machine named "Bertha" is only one-tenth of the way toward completing a 1.7-mile tunnel. The tunnel will carry Highway 99 traffic and allow the removal of the aging Alaskan Way Viaduct along the Seattle waterfront.

The total viaduct replacement is estimated to be a $3.1 billion project.

Crews recently spent more than 100 hours examining Bertha's cutterhead and the area in front of the machine, trying to determine what was causing problems. Inspection crews found a hard object more than 3 feet wide stuck in the machine's massive spokes, and they also found metal and plastic piping in the machine but have not concluded what exactly caused the problems that halted digging.

Officials previously said the machine also ran into an 8-inch-diameter metal pipe that had been left in the ground in 2002 after the Transportation Department checked groundwater in the area.