Stabilization & the harmonious blending of highway interchange slopes

June 11, 2018

The Interstate 90 Bridge over the Mississippi River between La Crosse, Wis., and La Crescent, Minn., is a heavily used commuter route and part of the longest interstate highway—I-90—in the country, spanning from coast to coast and providing important commercial and defense infrastructure for the entire nation. 

Bridge design project objectives

Providing a new, structurally sound I-90 river crossing bridge that achieved current structural and geometric standards on this important regional river crossing was the goal of a three-year, $187.5 million project. It would provide a safer, higher-capacity reconstructed interchange. 

The reconstructed bridge and interchange needed to fit naturally into the surroundings created by the bluff and river environment.

Key factors in the river bridge design plan included:

  • A 100-year design life;
  • A length of 2,593 ft and widths of 45 to 66 ft;
  • Two 12-ft lanes in each direction; and
  • 12-ft outside shoulders and 6-ft inside shoulders.

Slope protection design solution

Presto’s Geoweb 3D system was chosen to address both structural and aesthetic design requirements for 11 different slope application areas. The system confines and stabilizes topsoil and aggregate on steep slopes. Confined infill is stable on steep slopes of greater than or equal to 1H:1V and is minimally affected by surface runoff.

The slope stabilization areas featured a variety of conditions.

  • Vegetated slopes: One hundred six thousand sq ft of 6-in.-deep Geoweb sections were filled with topsoil and an erosion control blanket cover. The slopes varied between 2.5H:1V and 3.5H:1V, up to 48 ft vertically, around the bridge abutments.
  • Non-vegetated slopes: Forty seven thousand sq ft of tan 4-in.-deep Geoweb sections were chosen to match the local aggregate were placed over a non-woven geotextile and filled with aggregate.  The slopes varied between 2H:1V and 1.5H:1V, up to 45 ft vertically, under bridges. Vegetation was not an option in these locations due to the lack of exposure to sunlight and moisture.

In both applications, ATRA Anchors secured the Geoweb sections on the slopes. Presto Geosystems’ engineering team provided calculations and anchoring recommendations for all areas. This three-year-long construction project was completed in fall 2016.

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