Project Summary/Scope: A county highway near Mankato, MN required realignment due to growth in the surrounding area. The original highway was built into a steep mountainside and contained sharp curves, limited sight distance, and narrow shoulders. In some sections of the existing roadway, speed limits were reduced to as little as 20 mph. The final design for the realignment included a new roadway downhill from the existing roadway. Project partners decided on reinforced soil slopes (RSS) to achieve the new roadway alignment, and were able to stage construction of the RSS to permit uninterrupted access for area residents during construction.

The final product required two distinct RSS structures, a 1:1 slope between the existing and new roadways, and a 1:2.75 slope supporting the new roadway. This successful project represents one of the largest RSS project in the state of Minnesota, and resulted in a new alignment which allowed for a new 40 mph design speed over the majority of the two miles of affected roadway.

Complementary Technologies Used:  Gravel chimney and blanket drains to support substantial hillside seepage; stacked and vegetated geocell facing.

Project Technical Paper:  Lichty, N. and Gale, S. (2020) Realignment of County Highway with One of the Largest Geogrid Reinforced Slope Projects Constructed in the State of Minnesota, Geosynthetics 2020 – Case Histories, 8-10 March 2020, Charleston, SC.

Date Case History Prepared: 23 December 2020.

Case History Prepared By: Melissa S. Beauregard