Gravity walls go up quick on busy Nashville road

By: Jake Manthei

More than 40,000 cars travel along Hillsboro Pike each day, one of the busiest thoroughfares in Nashville, Tenn. Until recently, the road lacked a left-turn lane, which created an extreme amount of traffic backup.

To expand the roadway, banks on the east side of Hillsboro Pike required extensive retaining walls that would allow the Tennessee Department of Transportation (TDOT) to save existing landscaping and utilities while minimizing lane closures. In addition, it needed a retaining wall that could be built directly in front of an existing stacked stone wall that TDOT did not want to dismantle. The only kind of retaining wall that was feasible for this site was a gravity retaining wall that did not need reinforcement.

Based on these requirements, TDOT selected Redi-Rock large block retaining walls system . By using gravity, the 1-ton blocks rely on their mass to create tall gravity walls that require minimal excavation. The blocks used in this project were manufactured at Architectural Wall Solutions, just six miles from the jobsite. In addition, the blocks provided an aesthetic appeal to the site.

“The retaining wall had to go in before they could widen the highway, so the amount of time it required to put in the retaining wall affected the time it took them to get to the paving operation,” said Jim Hammann, manager of Architectural Wall Solutions. “The ease of installation of the system was definitely a factor.”

For this project, engineers designed both walls as gravity solutions that did not require reinforcement. The north wall stands 12.5 ft tall at its highest point and extends for 268 ft. To build a gravity wall this high, the design required one course of planter blocks, which increased the setback of the wall. The south wall was designed to stand 7.5 ft tall at its highest point and 350 ft long. In many places, the face of the south wall was built within 6 ft of the face of the existing stone wall.

Because this is such a busy roadway, construction of the retaining walls was allowed only between the hours of 9 p.m. and 6 a.m., and only one lane of traffic could be closed during that time. With only one lane of space to use as a construction area, Mountain State Contractor’s installation crew had to work closely with Architectural Wall Solutions to make the project progress smoothly.

“We did quite a significant amount of coordinating to make sure they had the blocks when they needed them and that we didn’t run out,” Hammann said. “Our plant was only 6.5 miles from the jobsite, so we were able to make a turnaround from empty trailer to full trailer in about an hour.”

The wall installation took about two weeks including rain delays. As the crew became more experienced with installing Redi-Rock , they were able to install 995 sq ft of wall in a particular 8-hour shift.