poor drainage conditions and structural deficiencies in a 70-foot single run and 790-foot double run 54-inch diametercorrugated HDPE drainage pipe threatened the storm sewer’s failure in the CrownPointe Commerce Park in early 2018. Engineers recommended removal of more than half the failing system and replacing it with concrete pipe.
Poor drainage conditions and structural deficiencies in a 70-foot single run and 790-foot double run 54-inch diametercorrugated HDPE drainage pipe threatened the storm sewer’s failure in the CrownPointe Commerce Park in early 2018. Engineers recommended removal of more than half the failing system and replacing it with concrete pipe.
In one section of the failing pipeline, and only “if expedient measures are taken,” the engineers gave the option of a structural liner or replacement with concrete pipe. According to the engineering analysis, the pipes were “FAILED” with one “active collapsed area.”
Past problems at CrownPointe indicated issues underground. The alignment of the drainage easement traverses the parking lot of a warehouse occupied by a prominent moving company and a major overnight shipping company. A truck court occupies the easement where tractor-trailers park and maneuver into cargo bays. The overnight delivery company’s employees recalled an incident in which a section of the parking lot collapsed, resulting in a “hole” beneath the truck cab’s front tires during a cargo transfer operation. They did not report any injury or property damage, but the driver managed a shimmy-shuffle maneuver to extract the truck.
Original Design
The original drainage system was designed in 1998. The engineer’s plans indicate the double run of 54-inch HDPE pipe had between 2.5 feet to 4 feet of backfill cover from finished grade to top of pipe. The current version of ASTM D2321 requires 54 inches of cover (one diameter) for 54-inch plastic pipe. Based on site observations during removal and replacement, the parallel spacing between the plastic pipes was approximately half a pipe diameter. The plastic pipe industry recommends 27 inches spacing between parallel 54-inch plastic pipes. For concrete pipe, spacing between parallel pipe runs is not of great concern because concrete pipe is less dependent on lateral soil support than plastic pipe. The Engineer of Record, however, and not a pipe vendor’s generic table, is ultimately responsible for specifying the proper pipe envelope dimensions, soil types and compaction requirements to ensure a resilient structural system
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