Mission Critical Corrugated Metal Pipe (CMP) Repair

The potential cause of the sinkhole was failure of the CMP storm drain. The CMP experienced flattening of the profile, corrosion of the invert, and open joints. The potential causes of the CMP failure were the naturally corrosive nature of the soils, age of the culvert, poor workmanship in installing the culvert, and poor design. This project encountered numerous complicating factors including: (1) the roadway is sole access to critical base assets. The roadway remained open to restricted weight loads, less than normal requirements; (2) access and work area required the base and contractor to expedite clearing affected areas for permitting including biology, archeology, Native American, surveyor, etc.; (3) the existing CMP culvert was comprised of several section of CMP with various shapes and sizes. The largest of these was approximately 7-ft in diameter; (4) there were three grade breaks within the CMP alignment. The breaks allowed the storm water to fall approximately 2 ft over a run of 2 ft; (5) the existing alignment for repair was approximately 270 ft in length with a left horizontal curve with a radius of approximately 1,500 ft and approximately 120°; (6) the CMP was galvanized steel with a bitumen lining; (7) the culvert invert was cast concrete; (8) the proposed tunnel construction replacement method had to negotiate the curved alignment, consume the CMP, and then allow for abandonment or removal of the proposed construction equipment while still supporting the failed ground above the tunnel termination. The tunnel replacement ended at the concrete tunnel, start of the railroad easement; (9) the work area and access were tightly controlled to avoid protected habitat and sensitive cultural resources while maintain a safe grade; (10) the work area required a method to divert storm water in the event of rain. The channel is subject to flash flooding; and (11) short design and construction schedule.