When flood-borne debris severely damaged one of the piers that supported the Red Jacket Trestle Bridge on the Le Sueur River in Minnesota, the historic bridge needed to be rehabilitated quickly.
The Red Jacket Bridge was constructed in 1874 and once served as a railroad bridge along the route of the historic nearby Red Jacket Mill. The bridge today serves as a popular multi-use recreational trail crossing over the Le Sueur River, on its way from Mankato to Rapidan, Minnesota.
During a flooding event, one of the support piers was significantly damaged and the bridge was near collapse, causing unsafe conditions for recreational users and vehicle traffic. The bridge was in such a precarious state that it forced Blue Earth County to close the bridge, as well as a section of roadway that runs under the bridge and adjacent to the river below.
The project included removing and salvaging the main span, replacing the south stone pier with a cast-in-place concrete structure with form-lined stone facing to match the existing piers and resetting of the salvaged span.
This project used state-of-the-art engineering techniques to preserve an historic bridge and showed the public that a rapid response by engineers and public agencies could quickly come together to save this valued recreational resource in the community.
SEH provided an unprecedented level of prompt action to assess the damage, and quickly salvage the girder span and trestle from further damage while obtaining approval from the Federal Emergency Management Agency (FEMA), the Minnesota Department of Transportation (MnDOT) and the State Historic Preservation Office (SHPO).
With over half its cross sections missing, the precarious state of the pier prevented anyone from getting near it because of the concern that the entire bridge would collapse. Survey results confirmed that it would be impossible to safely repair the pier and it would need to be replaced. Parallel seismic testing verified the presence and length of the piling beneath the center pier that was to remain.
From an economic and sustainable design standpoint, the decision was made to salvage the superstructure of the bridge and re-use the 90-foot section of the existing span. With this in mind, SEH designed a massive new 51-foot-tall pier shaft measuring 30 feet by 11 feet at the base. The replacement pier was designed as a hollow concrete structure, which reduced costs and eliminated the potential for thermal cracking problems during curing.
In the end, this project preserved the historic integrity of a bridge that is eligible for the National Register of Historic Places, saving it from collapse and safely maintaining its use as a popular recreational trail crossing. In addition, the project involved a long-lasting, cost-effective solution that is designed to prevent damage from future floods.
Jeff Johnson, PE is a structural engineer and leader of the Company’s Structural Practice Center in Minnesota, North Dakota and South Dakota. His experience includes several hundred bridge design and rehabilitation projects across the Upper Midwest. Contact Jeff