The Metropolitan Sewer District of Greater Cincin-nati needed to repair a rusty, weak and deformed section of 78-inch corrugated metal combined sanitary-storm sewer pipe running under a pharmaceutical company drug research and manufacturing site.

The size of the pipe and its location under an active industrial plant presented unique challenges for MSD senior engineers as they reviewed rehabilitation options.

The addition of a second story to the drug company building required a structural solution. Manhole access was next to an active multiple-entry loading dock on one side and next to railroad tracks on the other. In addition, the pipe was laid on a curve and had several active service connections.

The district solved the problem by using the Sekisui SPR spiral-wound pipe renewal system, which enabled the repair to be com-pleted without bypassing the pipe.

No flow interruption

The pipe location precluded bypassing the active flow because routing of the bypass pipe would have affected the company’s loading dock operations. There was also the risk of a rapid flow increase in case of rain, and district officials found the cost of bypass pumping to be excessive.

Seeing that a standard solution was not feasible, the district staff explored the Sekisui spiral-wound technology, which had never been used before in Cincinnati. They determined that the technology would provide structural renewal without bypassing and would negotiate the curved pipeline. It would also enable reconnection of active service laterals, accommodate daily flow, and provide safe conditions for the installation crew.

The staff found the Sekisui process simple and straightforward. Cleaning revealed that the interior of corrugated pipe had significant rusting in the invert, including holes through to the surrounding soil. This meant the pipe was structurally compromised and that continual high- to low-flow conditions would allow scouring of the external soil, weakening support and ultimately resulting in a structural failure under the factory floor.

Getting it done

After the pipe was cleaned, workers lowered a purpose-designed hydraulically powered winding machine loaded with the SPR PVC profile material into the sewer while it was still in service. A roller interlocking mechanism automatically rotated around the pipe walls, progressively winding the lightweight, corrosion-resistant material to create a new pipe inside the old.

The T-shaped rib profile material, with steel reinforcement, securely locked into place, forming a strong and durable new pipe. On completion of spiral winding, new pipe bulkheads were constructed at each end, and the service connections were joined.

Next, workers injected a high-strength cementitious grout into the annular space between the SPR pipe and the CMP host pipe walls. The SPR pipe was supported during grouting with a temporary in-ternal bracing system, designed to prevent pipe flotation and to main-tain the desired new pipe shape.

Efficient and cost-effective

The district repaired 105 feet of aged CMP combined sewer pipe in two weeks from start to finish with no disruption of service and with no inconvenience to the pharmaceutical plant. Because the installation was efficient and cost-effective, the district is considering it for future sewer rehabilitation jobs.

“This installation has been successful at least in its initial phase, and if the long-term results are as good as we suspect they will be, the Sekisui process has great prospects for future use,” said Mike Flanders, senior engineer with MSD.