St. Anthony Falls I-35W BridgeGeolocation: 44.979, -93.2649

 Terracon's geotechnical engineers provided on-site evaluating and solutions for the I-35 St. Anthony Falls bridge.

On Aug. 1, 2007, the I-35W Bridge over the Mississippi River in Minneapolis, Minn., collapsed, killing 13 people and injuring 100 others. Just days after the collapse, the Minnesota Department of Transportation (Mn/DOT) began planning a replacement bridge, naming it the St. Anthony Falls I-35W Bridge. Construction of the new bridge began in Oct. 2007. Mn/DOT chose to accelerate construction of the I-35W Mississippi River replacement bridge project using the design-build procurement process. Shortly after construction began, Flatiron Constructors, Inc. (FCI) encountered a unique condition that required shoring for a critical component of one of the bridge bents. The team quickly ruled out standard shoring options and contacted Terracon for this schedule-critical design. Within eight hours of being contacted by FCI, nationally recognized design experts from Terracon’s Cincinnati office were on-site evaluating the conditions providing preliminary recommendations. FCI’s previous geotechnical engineering consulting experience with Terracon gave them confidence in bringing Terracon onto the team. Terracon engineers completed the design during the Thanksgiving holiday weekend to keep the project on schedule. A preliminary design was completed on Nov. 23 and finalized on Nov. 26, meeting FCI’s deadline. To complete the project, a temporary retention system was designed for the Northbound Pier 4 drilled pier cap foundation. Working with FCI, Mn/DOT, and the FHWA, Terracon completed and implemented the entire design in 15 days. Construct ion of the design began on Dec. 5; just hours after Mn/DOT approved the design. Typically a shotcrete facing is preferred for load transfer; however, due to extremely cold weather conditions, speed of construction, and associated costs, Terracon was asked to develop a creative facing solution. Facing of the 52-foot open-cut excavation consisted of a Mn/DOT Class IV non-woven geotextile and Tecco steel wire mesh attached to the rock nails with specially designed steel bearing plates. Terracon also recommended installing a chain link fence over the entire excavation face for surface protection. In addition to the shoring design, FCI hired Terracon to assist with some difficult drilling that was falling behind schedule. With one days notice, Terracon mobilized a drilling rig from its Cedar Rapids, Iowa, office and hired a local subcontractor to complete the necessary drilling to return the project to its original schedule. Drillers battled difficult weather and subsurface conditions to obtain high quality samples that exceeded expectations, and production rates that had previously been unattainable.

Minneapolis, MN