The Holes Creek Tunnel Project in Dayton, Ohio, was a 4,400-foot microtunneling installation established as part of a plan to eliminate sanitary sewer overflows in the Holes Creek Drainage Basin. Increased sewer loads brought on by development in the surrounding areas had resulted in overflows during periods of heavy rain. Cracks and leaks in manholes and pipes were primary culprits.
When Montgomery County first planned the project, the design called for open-cut construction with alternate routing used to avoid depths of more than 25 feet. This proved impractical when several locations were found with depths exceeding 30 feet. There also were several other impediments to open-cut installation. The pipeline crossed both underground and overhead utilities. It was impossible to close down heavily used roads adjacent to the construction. The native limestone material would make open-cut difficult. And, finally, environmental concerns were raised because the pipe passed through wooded areas.
Microtunneling was deemed necessary for the entire project. Hobas Pipe won out over the other materials allowed in the specifications because it was corrosion resistant and could conform to the varied conditions that were encountered during jacking.
County engineers specified only pipe that was corrosion protected or resistant. This was done to ensure a long life for the sewer line, important because of the environmental considerations of the sewer?s location. Because of the burial depths, future rehabilitation of a corroded line would be very expensive.
The county employed Woolpert LLP of Dayton, Ohio, for the engineering services. Bowen Engineering Corp. of Fishers, Ind., was awarded the installation contract.
Two main factors influenced Bowen?s selection of Hobas Pipe: the lower installed cost and the pipe?s smooth and consistent outer diameter, which reduces friction resistance, lowering jacking loads. Also, because of its light weight it can be handled with less expensive equipment.
Approximately 4,400 feet of Hobas centrifugally cast fiberglass reinforced polymer mortar pipe was used in both 36- and 48-inch diameters. Only 10 drives were required to complete the project. Included were 1,100 feet of 36-inch, 300 ton jacking pipe and 3,300 feet of 48-inch, 400 ton pipe. The pipe was furnished in 10-foot sections with push-together, flush, gasket-sealed joints.
Average drive lengths were 362 feet for the 36-inch pipe and 467 feet for the 48-inch pipe. The longest drive was 688 feet through shale and limestone with a maximum jacking load of 280 tons. The average jacking load for the entire project was only 100 tons.
Only one leak was discovered during the five psi, 28 minute leakage test after the pipe was installed. It was caused by a gasket that was rolled during assembly, and was permanently repaired with a fiberglass lay-up applied internally.
