Perfect solution

Roads & Bridges / December 02, 2008

During normal precipitation conditions, soil under the surface of the ground expands and contracts with the variations in moisture levels. However, extremely dry seasons can cause underlying layers of soil to shrink drastically and cause the earth above to fracture and depress. This is what occurred with U.S. 221 in Taylor County, Fla. As the result of a draught, large cracks in the pavement threatened the safety of residents who frequently traveled the road. Since this section of road had failed before, Florida Department of Transportation (FDOT) District 2 needed a design and product that would remain strong and sturdy.

FDOT teamed with Saliba Engineering Inc. and Anderson Columbia Co. Inc. to promptly address the emergency situation. Both the engineer and contractor had previous experience with Contech Construction Products Inc. They had partnered with the company on past projects and knew that Contech would have the right solution for U.S. 221. A reinforced aggregate system containing Tensar Biaxial (BX) geogrid was the solution chosen for Taylor County because of the performance properties of the geosynthetic reinforcement. Additionally, Tensar is accepted by FDOT and listed on their 501 Index for approved products. It was the perfect solution for the project.

The geogrid is manufactured from continuous sheets of select polypropylene. It is manufactured through a specialized process that results in production of a geosynthetic that provides maximum aggregate confinement and lateral restraint. The structural geogrid permits heavy construction loads on sites with weak soils, thus eliminating all or most other foundation and soil stabilization work. The geogrid provides a reliable, cost-effective method for increasing the stability of weak soils in a variety of applications including streets, parking lots and foundation systems. By internally reinforcing all types of soils and construction fill material, geogrids create a stiffened, reinforced prism capable of supporting critical, engineered structures.

Installation of the geogrid followed an uncomplicated 10-step process, beginning with the removal of the existing roadway. Since the ratio of the aggregate base size to the subgrade particle size did not satisfy the required piping ratio to ensure particle separation, a series of separation fabrics—also provided by Contech—was laid, along with sand, limerock and asphalt.

The geogrid provided confinement of the aggregate particles in the base course, thereby maintaining structural capacity and improving the performance of the pavement system. The entire process was finished with 3 in. of 12.5 structural asphalt and a 1.5-in. layer of 12.5 frictional asphalt.

The project, completed in two months, was a success. The geogrid provided a reliable and cost-effective solution for U.S. 221. As a result, the road is no longer plagued by large fractures and is now a safe and sturdy means of transportation for Taylor County residents and visitors.

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