Test shaft to be gold mine of data for new 35W bridge

Last update: November 21, 2007 - 6:12 PM

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SIDEWALK TOURS

Bridge project managers are giving "Sidewalk Superintendent Talks" about the project every Saturday. The free tours start at 11 a.m. at the Grandma's Saloon parking lot in the Seven Corners area and go across the 10th Avenue Bridge adjacent to the construction site.

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On a day when many Minnesotans are testing the load limits of their stomachs at the Thanksgiving table, builders of the new Interstate 35W bridge will be down on the Minneapolis riverfront to test the limits of a concrete shaft that extends nearly 100 feet underground.

Such shafts will support the bridge's main piers. The one to be tested Thursday was built as a test shaft, and pressure from two hydraulic jacks deep in the earth will be applied until the shaft moves. The force required to move the shaft should be greater than the forces created by the weight of the bridge.

This shaft won't be used to support the bridge's foundation, but it will help engineers determine the final design of the real ones.

It is the second test shaft that has been dug. The first, which went down about 110 feet, hit some pressurized artesian water, so workers dug again and went down about 95 feet.

Although the artesian water was unexpected, the need for the second shaft isn't expected to delay the project, said Jon Chiglo, the state Department of Transportation's project manager for the bridge. "That's why we do these test shafts," he said.

Neighbors of the bridge site will be happy to know that the pile drivers are taking the holiday off. (They will resume Friday and Saturday from 7 a.m. to 5:30 p.m.)

MnDOT said Wednesday that pile-driving is 80 percent complete and should be finished sometime next week. There also will be no night shift work for the remainder of this week.

The bridge is scheduled to be completed by Christmas Eve 2008.

JIM FOTI