The bridge over Hay Creek in Chippewa County, Wisconsin was going to be reconstructed. This was the first time the State used FHWA EDC Initiative for a GRS-IBS project for a Geosynthetics Reinforced Soil Integrated Bridge System (GRS). The project was chosen in November 2011.
The Design
The site was chosen as part of a much larger roadway project. GRS is an engineering structure that uses layers of geosynthetic reinforced aggregate. The bridge was planned to be a 40° single span, cast-in-place bridge. The DOT or Department of Transportation used standard design procedures including hydraulic analysis, geometry, load analysis, external and internal stability, and a total plan set. FHWA Design Manuals and the completed FHWA standard plan sheets were brought in. The innovative design aspects included the slab-span superstructure, the use of modular blocks, and existing soft soils underneath the abutment. RSF or reinforced soil foundation was used in the area of soft soils after removal.
Construction
Modular block was applied as the facing units for the abutment. As FHWA recommended, 4800 lb ft tensile strength geotextile was chosen for the bridge approach area, the reinforced zone, bearing bed, and the RSF. It was decided that Mirafi® HP770PET woven geotextiles would be the best choice. The abutments were built in lifts using a 1.25-inch dense graded based in the bridge approach area and RSF. A standard open graded base was constructed within the walls.
Performance
The construction of the GRS-IBS took approximately one week to assemble. The scheduled two weeks were less than the standard driven pile abutments. Construction of a GRS-IBS will permit less construction time by using lighter, more mobile equipment. The abutments will be monitored for vertical and horizontal movement There was a lot learned during the design and construction during this project. The Wisconsin Department of Transportation will continue to review and promote GRS-IBS for future abutments where needed.
