When planning and designing roadway projects, stable and resilient road shoulders are crucial to the performance of the road or highway and the safety of its travelers. These unassuming strips of land that run adjacent to the pavement provide space for vehicles in the case of an emergency and a stable recovery area for drivers who need to veer off the travel lane to avoid an accident. They also protect the pavement edges from traffic damage and often function as a stormwater management system.
The Challenge: Stabilizing a Vegetated Road Shoulder
The $45 million, 3.2-mile Mack Hatcher Parkway extension project in Franklin, Tennessee, included the construction of a vegetated road shoulder along a portion of the new roadway. The Tennessee Department of Transportation (TDOT) required a low-maintenance, economical, and safe solution for this vegetated road shoulder.
Initially, a rolled paver product was specified; however, this solution was cost-prohibitive, so engineers worked with Jen-Hill Construction Materials to provide a more affordable solution that met their requirements for a stabilized, vegetated road shoulder.
The Solution: GEOWEB® 3D Soil Stabilization System
Project engineers chose the GEOWEB® Soil Confinement System to stabilize the road shoulder along the parkway. Compared to a rolled product, the GEOWEB system provided a thinner cross-section, was easier to install, and lowered the overall project cost.
The contractor placed 188,000 square feet of GEOWEB GW30V4 (4-inch cell depth) sections over a woven geotextile. The GEOWEB sections were connected using the ATRA® Key—most efficient geocell connection device—at each end-to-end connection. Once installed, the GEOWEB geocells were infilled with an engineered fill consisting of 70% crushed aggregate and 30% topsoil mix. Crushed aggregate provides the required load support capability while the topsoil allows for root penetration, leading to stronger, healthier vegetation. Sod was rolled over the top of the filled GEOWEB sections to complete the installation.
Low-Maintenance Green Solution
In addition to project cost savings, the GEOWEB system also offers long-term protection against road shoulder rutting and degradation of the adjacent pavement edge. Together, these benefits help reduce costly maintenance and repairs that result from vehicles traveling off the edge of the pavement and onto the road shoulder. Moreover, a vegetated shoulder also improves stormwater quality and offers a green and aesthetically appealing solution compared to conventional crushed aggregate road shoulders.
Benefits of the GEOWEB System for Stabilized Road Shoulders
- Creates permeable, stable shoulders that reduce rutting and eliminate degradation of the shoulder and adjacent pavement edge.
- Stabilizes infill material and controls shearing, lateral and vertical movement.
- Increases the effective structural number, cutting fill requirements and costs in half.
- May allow use of lower quality, less costly on-site infill materials.
Project Results
More than one year after installation, the City of Franklin and TDOT are satisfied with both the performance and aesthetics of the project.
Editor's Note: Scranton Gillette Communications and the SGC Infrastructure Group are not liable for the accuracy, efficacy and validity of the claims made in this piece. The views expressed in this content do not reflect the position of the Roads & Bridges' Editorial Team.
