Overpass options

November 2011 » Features » PROJECT CASE STUDY
Use of polymer geogrid reinforcement and locally available backfill give MSE retaining walls a cost advantage.
Aaron Smith
Double rows of tightly spaced piles support the abutments for the Delaware County Road 124 bridge over a CSX railway line.

As transportation departments look for innovative and structurally reliable ways to stretch tight budgets, mechanically stabilized earth (MSE) retaining walls are rapidly gaining acceptance. MSE retaining walls deliver structural performance and service life at or above the conventional poured-in-place construction process, but at a much lower cost. In addition, their wide range of appearances and finishes make them attractive (literally and figuratively) when compared with other types of retaining walls.

Project
County Road 124 overpass, Delaware County, Ohio

Participants
Ohio Department of Transportation
Trucco Construction Co. Inc.

Product application
Tensar ARES Retaining Wall System with HDPE geogrids allows use of locally available backfill.

In Delaware County, Ohio, a growing area near the state capital of Columbus, the Ohio Department of Transportation (ODOT) wanted to bridge the heavily traveled County Road 124 over the existing CSX railway and was looking for an economical solution for the proposed retaining walls. The ARES Retaining Wall System was specified as an approved MSE wall solution, and was ultimately chosen by Trucco Construction Co. Inc. for use on the project. Many factors went into the decision to install the ARES walls, but the overwhelming advantage was the ability to use locally available backfill material with the extremely inert polymer geogrids, providing a cost savings for the overall project.

"By utilizing the Tensar ARES Retaining Wall System, we were able to take advantage of backfill material from a local source," said Randy King, vice president of Trucco Construction. "The ability to use this local material enabled us to be more competitive at bid time."

This was a considerable aspect of the Delaware County project because the aggregate that's required for steel reinforcement was not locally available and would have to be hauled from a further distance, resulting in additional transportation and material charges.

"We trucked in approximately 100,000 tons of granular backfill, which equated to around 5,000 loads," said King. "Given this quantity, utilizing less trucking was definitely a key component to the success of the project."

Design and aesthetic challenges
Two retaining walls were designed for the site totaling 45,000 square feet, with maximum heights approaching 40 feet and combined lengths of approximately 1,600 linear feet. Among the challenges for the project were double rows of tightly spaced piles supporting the bridge abutments, and specified plain smooth form finish for the panels. Smooth panels can be a challenge for any MSE retaining wall mainly because there is so little room for error aesthetically. The panels can be damaged easily, and the slightest misalignment, even if the wall remains within tolerance, is more visually apparent.

ARES Retaining Wall Systems incorporate Tensar uniaxial, high-density polyethylene (HDPE) geogrids connected to the panel face. The concrete panels are cast with polymer tabs on the backside of each panel and then connected to the geogrid reinforcement during construction by a bodkin bar, also made of HDPE. This corrosion-resistant connection and reinforcement can be used in a wide variety of backfill materials, including high and low pH extremes, sulfates, and where resistivity is an issue with locally available materials, as was the case with the Delaware County project.

When Trucco Construction was commissioned for the project there were other MSE systems considered for the job. Economics was a driving factor, but a key element in the decision was the onsite assistance provided by Tensar.

"A line item was set up in the proposal which enabled Tensar to send a technical representative, Jeremiah Riggio, to the site for five days," said King. "This created a team atmosphere in which Trucco Construction, along with ODOT, could work closely with Tensar to ensure that the walls were being constructed per the plan requirements, as well as the manufacturer's specifications. It resulted in a smooth process for all parties."

"Trucco's overall professionalism and attention to detail during every stage of construction was impressive," Riggio said, "and resulted in one of the best ARES installations I've seen."

A specified plain smooth form finish for the MSE retaining wall panels left little room aesthetically for error caused by panel damage or misalignment.

Aaron Smith is the Northeast regional sales manager for Tensar's Grade Separation Solutions. Jennifer Cargill Gardner is the marketing manager of Grade Separation Solutions for Tensar and has been in the geogrid industry for more than 18 years


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