A three cell 7ft x 7ft drainage culvert (A tunnel carrying an open drain under a road or railroad), runs underneath Northpointe Boulevard in Pensacola. Flow of water through the culvert had caused soil washout at the downstream end. Borings were taken inside the culvert and it was determined that a void up to six feet deep had been created, which extended approximately 25 feet inwards from the downstream end. This erosion passed behind two angled wing walls on the ends of the culvert, causing a failure of these walls. This led to concern that the culvert would begin to settle and cause the road overhead to collapse.
Alpha Foundations was chosen to fill the void and stabilize the culvert by installing PolyLevel 400 Hydrophobic (PL400H). PL400H is a lightweight, hydrophobic, two part polyurethane foam with a density of four pounds per cubic foot (pcf), and a compressive strength greater than 8,500 pounds per square foot (psf). Through boring measurements, it was determined that approximately 38 cubic yards of void would need to be filled to prevent the structure from failing. PL400H was first free sprayed at the end of the culvert, where the void was uncovered, to dam off the exposed area. PL400H was then injected using 5/8 inch diameter holes drilled through the structure’s bottom slabs. To not affect the flow rate of runoff, elevation was monitored during the injection process to verify the angle of the culvert was not changed. This installation process resulted in the void being successfully filled, stabilizing the culvert against settlement.