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.
Subjects: highway 53 relocation project, foundation loading testing, statnamic testing
Author: Paul J. Axtell, P.E., D.GE, David S. Graham, P.E., Joseph D. Bailey P.E.
Publisher: ISM, DFI, ADSC