Canada’s tunnel saga offers lessons on Bertha fix

The Seattle TimesFebruary 14, 2014 

In this WSDOT photo from May 2013, the State Route 99 tunneling machine’s cutterhead was held aloft by a large gantry crane before joining other pieces of the machine in the 400-foot launch pit. The machine, often called Bertha, began tunneling under Seattle in summer 2013.


In its day, tunnel-boring machine Excalibore was the pride of Canada, 3 stories high and churning merrily westward through the port city of Sarnia, Ontario.

Just before it was to reach the St. Clair River, with Michigan on the horizon, inspectors in late 1993 found tiny particles of clay in the grease that lubricated the bearing seals. Rather than risk a breakdown under the river, the team building the Canadian National Railway tunnel stopped for repairs a mere 820 feet from the starting line.

Subcontractors dug a deep vault in front of the machine, lifted the cutterhead away, and fixed the damaged seal parts a few feet inside.

After seven months, Excalibore resumed digging, and the one-mile tunnel got done before the end of 1994.

Seattle will probably learn a lot this year from the chronicles of Sarnia.

Contractors here will need months to fix Highway 99 tunnel-boring machine Bertha, after seal damage allowed sand into the bearing assembly that steadies and spins the cutterhead.


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