One of the exciting aspects of working in stormwater is coming up with unique ways to solve repair problems. At this site, the existing outfall pipe was corroding causing water to erode the soil along the outside of the pipe, a condition known as piping. Eventually, it caused a sinkhole that was visible from the surface. This condition can lead to a failure of the embankment with catastrophic results. Check out this video of a failure.
Positioning the new lining
Rather than dealing with the high cost and disturbance of replacing the entire pipe, we lined the corroding corrugated metal pipe (CMP) with a smooth walled HDPE pipe. The pipe we used was Snap-Tite manufactured by ISCO Industries. Made specifically for this purpose, this pipe actually improved the hydraulic performance of the barrel while significantly extending the lifecycle of the structure. The void between the two pipes was pumped with grout. Of course, the sinkhole was also repaired with compacted clay.
With our design/build approach, we reduced the owner’s cost significantly while accelerating the schedule.
Sustainable Stormwater Management 
