Mt. Laurel, AL
GEOTECHNICAL EXPLORATION: Building and Earth Sciences
STRUCTURAL DESIGN OF RETAINING WALLS AND FOOTERS: Structural Design Group
LANDSCAPE ARCHITECT: Nimrod Long and Associates
SANITARY FORCE MAIN DESIGN: Engineers of the South
The Dunnavant Square Cooperative District contacted Sain Associates to review the feasibility of installing an underground tunnel across Shelby County Road 41 at Dunnavant Square. The purpose was to create a safe pedestrian crossing connecting Dunnavant Square and the Town of Mt. Laurel. Dunnavant Square is a mixed-use development located across from the Town of Mt. Laurel, Alabama. Mt. Laurel is a master-planned New Urbanist community with a mix of residential and commercial uses. The community encourages a lifestyle of leaving the car at home and walking, biking, or even taking the golf cart to neighborhood shops and restaurants. Introducing a new commercial development across a busy high-speed road with no accommodations for a safe crossing posed a problem. A traffic signal was not warranted nor desired by the County, as it would impede traffic flow on the heavily traveled roadway. The idea of an underground pedestrian tunnel was born to maintain traffic flow.
The project’s objectives included accommodating walkers, bicycles, and golf carts which influenced the size and location of the tunnel. After evaluations to ensure the tunnel would not flood, it was decided the tunnel floor would be set at an elevation so the existing grade of CR-41 would be maintained and to ensure adequate drainage.
To meet the Americans with Disabilities Act standards, Sain recommended installing an adjacent sidewalk at the maximum 5% longitudinal slope by utilizing a longer length and switchbacks. The beauty of Mt. Laurel is one of its best-known traits; therefore, it was essential to blend the landscaping and aesthetics of the tunnel and retaining walls with the natural beauty of Mt. Laurel. A solar-powered panel was installed outside the tunnel to power the lights mounted inside the tunnel allowing nighttime use.
Several utilities were relocated, including water, sewer, gas, power, phone, and cable. The waterline relocation was located on the shopping center side of the tunnel. The gas line would run parallel to the water, and both would be relocated under the tunnel and adjacent retaining walls, then continue parallel to CR-41 in a narrow area between the retaining wall and grocery store parking lot. To resolve a concern of line maintenance, Sain’s team designed an underground shore wall that will allow the water and gas lines to be exposed without impact to the adjacent parking lot.
To maintain traffic on CR-41 throughout the tunnel installation, Sain designed a diversion route across the adjacent graded commercial site to route traffic off the existing CR-41 alignment. This allowed enough space for the tunnel to be installed in its entirety.
Opened in September 2018, the Dunnavant Square pedestrian tunnel beautifully accomplishes the project goal of providing safe accommodations for pedestrians, bicycles, and golf carts to cross CR-41 and improves connectivity in the greater Mt. Laurel community.