CMP Culvert Abandonment
Culvert pipe abandonment using cellular concrete in Pittsburgh, Pennsylvania
A 40″ corrugated metal culvert pipe failed, causing a large sinkhole to form in the back yard of a single family home. The municipality was responsible for repair, and inspected the pipe. Inspection revealed that the pipe had significant off-set joints, a completely rusted away invert, and had started to oval. The pipe was up to 35 feet below grade, 250 feet long, and had 10 feet of drop. It ran within eight feet of the corner of a house, so considering the depth, had it collapsed, would have unquestionably affected the foundation of the home.
The pipe was installed by a private developer more than 30 years prior. The municipality installed a new system of pipes and inlet structures to bypass this stretch of pipe. After the new system was installed, the failed pipe needed CMP culvert abandonment.
Access to the area was good; concrete trucks could pull up to a manhole where material could be placed. The depth of the manhole for placement was 30 feet.
The municipality initially investigated using flowable fill, but due to the length of the pipe, would not have been able to be absolutely sure the pipe was completely full with a gravity placement.
Lightweight cellular concrete was chosen for the CMP culvert abandonment. Cellular concrete can be placed by tremmie pipe, which accommodated the nearly 40′ drop from concrete truck discharge chute to pipe invert elevation.
Cellular concrete is self-leveling to within a few inches per 100 feet, so it would be able to flow the entire length of the abandonment, past any restrictions and into any voids outside of the pipe.
CJGeo abandoned the pipe in place using lightweight cellular concrete. The pipe abandonment was done in a single day, and relied completely on gravity flow. Completeness of fill at the low end was confirmed by valved vent pipes through the bulkhead. The existence of extensive voids outside of the pipe was confirmed by extensive weeping of cellular concrete through the walls of the manhole structure that the abandonment terminated at.
Truck-batch cellular concrete generation was used on this CMP culvert abandonment job due to the low volume required.