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Rock County Finds Economical Solution with GRS-IBS

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Rock County Finds Economical Solution with GRS-IBS Luverne, MN
CMU Supplier: Concrete Materials
Contractor: Minnowa Construction
The bridge over a railway was closed for two decades before Rock County, MN, could afford to replace it. The new bridge is Minnesota’s first Geosynthetic Reinforced Soil Integrated Bridge System(GRS-IBS) and an economical option for the County.

Construction of the bridge was completed in less than two months. The existing bridge was

demolished and construction on the new one began. The facing element of this remote installation is smooth, dry stacked 8-inch (0.2-m) concrete masonry units (CMUs). Solid blocks were used at the wall base, up to the grade level, with hollow-core blocks above.

A shallow reinforced soil foundation supports the abutment. The foundation was constructed by excavating directly under the abutment to a depth of 3 ft (0.91 m), lined with geotextile, filled with compacted crushed road base and then wrapped and encapsulated with the geotextile.

Once the foundation was secure, the abutment was built with alternating layers of geosynthetic reinforcements (geogrids for most of the wall and geotextile for the top section) and gravel. Each layer of the geosynthetic material was extended across the top of the CMU at that level to create a friction connection, up to the top of the abutment, for a height of 22.5 ft (6.7 m).

The bridge abutment went up quickly. Three to five layers of the abutment were completed each day, about 220 to 360 ft2 (20.4 to 33.4 m2). Wing walls meet the abutment at an angle, so 45-degree CMU were specified to help speed construction. To create the superstructure, precast concrete box beams were installed on the top layer of the abutment and then the road approach was constructed.

The Federal Highway Administration and the Minnesota Department of Transportation are currently monitoring the Rock County Bridge. Sensors have been installed to measure pressure and ground movement. These will be used to evaluate any deformation and compare the findings with other bridges. Initial results show the abutments to be performing well and in keeping with other GRS bridges.

See how the GRS-IBS technology was successfully used for these projects:

Learn more about GRS-IBS technology.

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