Natchez Trace Undersealing

the PROBLEM

A section of the Natchez Trace Parkway, just north of Natchez, MS, experienced significant settling across both lanes of the parkway. The result was an uneven surface that presented driving hazards to motorists. The subsidence was caused by a combination of natural soil settlement and water infiltration, which undermined the roadbed and created unconsolidated soil and voids under the asphalt. The depression across both lanes made it difficult for vehicles to maintain a smooth and safe driving experience. The settlement affected a major traffic route, and any significant closure or repair work would cause substantial disruption to daily commuters and tourists, a key concern given the Parkway’s importance.

the SOLUTION

Structural Polyurethane resin was selected for this project due to its ability to provide quick and efficient undersealing and stabilization of the roadbed and lift settled sections of the asphalt. The resin expands within 20 seconds of injection, filling voids beneath the surface and creating a solid, stable foundation. Unlike traditional excavation or full-scale road replacement, the use of polyurethane resin offers a faster, less disruptive solution that can be applied without the need to close lanes for extended periods. With quick cure time, traffic flow was reduced to one lane for a short time with restoration of full flow immediately after repair was complete.

Injection of Polyurethane Resin: 5/8” holes were drilled into the road surface in a grid pattern across the affected section. The polyurethane resin was then injected under the roadway through ½” galvanized rods, where it expanded to fill the voids beneath the asphalt. This process stabilized the subsurface, lifting and leveling the surface to restore a smooth, safe road profile.

the RESULTS

Following the polyurethane resin injection, the road surface was restored to its original profile. The previously uneven sections were stabilized, with no further evidence of subsidence. The resin successfully filled the voids, stabilizing and undersealing the road surface, preventing any immediate risk of further settlement.

Benefits & Cost Savings: Compared to traditional methods like complete resurfacing or roadbed reconstruction, the polyurethane injection was more cost-effective and required far less time to complete, providing substantial savings in both time and money. The resin injection allowed for minimal lane closures and limited traffic disruption, which was especially important for a road used heavily by both locals and tourists.