Sunday, February 28, 2016

Big Bertha is Mining Once Again!

The State of Washington has given "provisional approval" to continue the SR99 tunnel bore.

To insure the past mistake in tunneling procedure, which resulted in a large sink hole just behind Bertha, the world's largest Tunnel Boring Machine (TBM).

That resulted in Governor Jay Inslee ordering tunneling to stop some 40 days ago, over the strong objections by Seattle Tunnel Partners (STP) manager, Chris Dixon. The governor requested Dixon review policies and procedures, and create a plan for continuing the dig.

To that end,three areas of operation have been beefed up:

•  A permanent Tunnel Manager will be appointed to back-up STP manager, Chris Dixon.

•  Three temporary specialist positions will monitor digging:
    a. A Tunnel Technical Director.
    b. A Tunneling and Soil Conditioning Specialist.
    c. A TBM Operational Specialist.

•  A through review of TBM Operator training.

If Bertha can keep it together over the next 260 feet, she will make a mandatory halt at "Save Haven Three," for a complete systems check and scheduled maintenance.

"Safe Haven Three" is located just west, adjacent to the SR 99 Viaduct.  The double deck Viaduct will be closed to traffic for the estimated two weeks it will take Bertha to bore beneath it.

Once past the Viaduct Bertha will really be on her own under the Streets of Seattle. Once "in the zone," there will be no way a rescue pit can be dug;  no space to install the Mammoet Lifting Device.

Another contentious issue is the resumption of barging spoils to Mats-Mats.

Since the barge lost stability and was severely damaged, Naval Architects will try to determine the reason the barge lost stability during loading, and make recommendations before barging can resume.

According to Chris Dixon, barges can haul away dirt twice as fast as trucks, allowing Bertha to advance twice as fast, or about 40 feet forward per day.

"Every 6½ feet, the machine pauses so crews can fasten another ring of the double-decked, four-lane highway tunnel, now predicted to open in spring 2018.

“We can do three rings per day with trucks until WSDOT lifts the barging suspension, after which we will be able to do up to six rings per day.”

Crews and staff will be inhaling anti-acid pills the remainder of ~9,000 feet to the North Portal!