The Job
The US Army Corps of Engineers (USACE) identified structural degradation in a double-barrel 84-inch reinforced concrete pipe (RCP) stormwater outfall at Hunter Army Airfield. This infrastructure lies beneath active taxiways and parking lots, making traditional excavation and replacement impossible. The USACE opted to slip-line the existing outfall with a 75-inch HDPE carrier pipe to restore structural integrity and prevent settlement under the airfield. Southeast Pipe Survey served as the prime contractor for the project. CJGeo was contracted to perform the critical annular space grouting required to secure the new carrier pipe within the original host pipe.
The Challenge
Initial designs for the repair used Cured-In-Place Pipe (CIPP), but the 84-inch diameter exceeded the capacity of on-site manufacturing equipment. Shipping pre-manufactured liners of this size created significant logistical risks. The design shifted to slip lining, which required filling a very narrow annular space. Active water infiltration at the RCP joints complicated the grouting process. Grout denser than water would typically be required to displace infiltration, but such density increases carrier pipe buoyancy. Managing buoyancy in a skinny annulus is difficult, as multiple grout lifts are often required to prevent the pipe from floating. Furthermore, all work had to be performed from outside the runway’s zone of influence without intermediate access points.
The Solution
CJGeo implemented a cellular grouting solution using CJ-Fill Standard (ST) at a density of 45 PCF. To address the infiltration, CJGeo worked with the prime contractor to seal the pipe joints using an expansive fiberglass joint sealer. This preparation allowed for a grout density that met the 300 psi compressive strength requirement while remaining light enough for a single pour. The carrier pipe buoyancy was managed entirely through internal water ballasting. This strategy eliminated the need for multiple lifts or complex sacrificial piping. Crews placed 278 cubic yards of cellular grout across two shifts. The process successfully filled the annulus of both pipe runs without shifting the carrier pipes or disrupting airfield operations.
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