MnDOT

Whitewater State Park Bridges

Bridge Rehabilitation and Preservation

In the 1930s, the Civilian Conservation Corps built four bridges in Whitewater State Park, just east of Rochester. The bridges are culverts constructed with a combination of stone masonry and metal arches that collect stormwater and protect Trunk Highway 74 as it passes through the park’s rolling landscape.

In 2016, MnDOT hired LHB to assess the bridges, which had degraded significantly over the decades. Additional soil covering had been laid over the culverts each time the highway was repaved, adding structural stress to the stone masonry headwalls. Mortar in the masonry had failed and many stones were dislodged or missing. The additional soil covering also created steep roadway slopes that were significantly eroded. LHB conducted a condition and site investigation, studied rehabilitation alternatives, documented environmental issues, coordinated with the MnDOT project team, and produced the final bridge preservation plan and roadway design.

Project Type Bridge Rehabilitation and Preservation
Location Minnesota
Completion Date August 2021

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Historic preservation

Much of LHB’s work was aimed at preserving the historic character of the bridges. The corrugated metal arches, assessed for safety and durability, were allowed to remain in place. Deteriorated stones were replaced and headwalls were repointed according to historic standards.

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Hidden strength

Riprap was used to protect the streambed and adjacent slopes. To maintain the site’s historic look, the designs buried the rock under reclaimed sediment within the stream bed and under seeded compost on the steep slopes.

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Reinforced slopes

Steep slopes, created by layers of soil coverings added to the bridge over the years, were reinforced using geogrid and layers of geotechnical fabric, taking pressure off the reconstructed masonry walls and reducing potential erosion.

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