Publication Abstract

Proceedings - 13th International Workshop on Micropiles - 2017, Vancouver, BC, Canada, (ISM, DFI, ADSC)

Paul J. Axtell, P.E., D.GE, David S. Graham, P.E., Joseph D. Bailey P.E.

The Highway 53 relocation project in Virginia, MN involves construction of a very tall bridge across a currently inactive iron ore mine pit. This pit is partially flooded and serves as the community’s drinking water source. The new bridge is 345 m (1,132 ft) long with a three-span, plate girder superstructure. Two intermediate 60 m (200 ft) tall piers are located within the pit. The foundations for the intermediate piers consist of bored pile groups installed using techniques common to micropile construction. Extremely challenging and highly variable subsurface conditions exist at the site, which range from uncontrolled iron ore mine waste fill to very hard rock that can also be highly fractured and abrasive. Despite the conditions, foundations up to 53 m (175 ft) deep were successfully installed using down-the-hole hammer methods and full-length permanent casing. An extremely aggressive construction schedule added to the difficulties. Full-scale foundation load testing using the Statnamic rapid loading method was conducted in support of the design and construction with a separate pre-design phase contract. This paper describes the Statnamic testing and associated unique behavior of a 406 mm (16 in) diameter test micropile.

 article #2645; publication #1033 (ISM- 2017)