Bridges

Drilled shaft foundations as an alternate to pneumatic caisson construction proved to be a considerable cost saving for the Interstate 80 bridge between Council Bluffs, Iowa and Omaha, Nebraska. Each of the two piers in the Missouri River has a foundation consisting of 13 drilled shafts 6' in diameter, extending 90' through alluvium, a socketted 12' - 18' into the Limestone bedrock. To facilitate construction, the general contractor dredged a sheet-piling cell full of sand to support Tri-State's crane mounted drill and related equipment.

This cantilevered lift bridge in Sheboygan, Wisconsin is supported by 7' diameter piers with 6.5' diameter rock sockets anchored into the hard Silurian Dolomites or Lake Michigan. The shafts were constructed to within 1% of plumb to a depth of 60' below the water surface.

Unusual geology under the St. Louis River in Cloquet, MN presented a unique challenge. A zone of shale had been metamorphosed by an igneous intrusion. Five of the eighteen six foot diameter piers were founded directly on Gabbro making conventional drilling impossible. The 6' casing was torqued into the Gabbro and as much as possible was removed. Then a 12" diameter downhole pneumatic hammer was used to drill 4 needle shafts 12 feet into the igneous rock in the shaft bottom to develop resistance to uplift from horizontal ice loading.