120” Storm Drain Reinforced Concrete Pipe

408′ Double Run of 120″ Special Design RCP with 47′ Fill Depth

Route 321 Emergency Restoration

Tennessee Department of Transportation

Hurricane Helene created a massive washout under Route 321 near Butler, Tennessee, closing a key regional highway that connects communities throughout Johnson County to schools, hospitals, and jobs. The damage required an immediate response from the Tennessee Department of Transportation (TDOT), which in turn called on Permatile to supply an engineered replacement structure capable of meeting an emergency schedule.

The plans called for a 408-foot double run of 120-inch special design reinforced concrete pipe. With the pipe designed to sit under 47 feet of cover, the immense structural loads would be far beyond any standard highway specification. At this burial depth, the vertical pressure alone creates enormous demands before accounting for traffic loads from a state highway.

Each pipe section was engineered by in-house Professional Engineers to handle the extreme burial depth. Special design shop drawings and calculations were required for this specific application, going beyond standard specifications to meet the unique performance demands. TDOT’s choice of this material was crucial, as reinforced concrete pipe has a long and successful history in such deep burial projects. Critically, Permatile’s ability to produce the highly specialized pipe sections off-site kept the entire recovery on its aggressive schedule.

This precast approach eliminated potential on-site casting delays and allowed site contractors to move forward with installation. Permatile was able to move from initial engineering to the final delivery of all 408 feet of specialized pipe in less than 90 days. The project demonstrated how off-site manufacturing of custom-engineered precast components can meet the demands of emergency infrastructure recovery.