TRENCHLESS TECHNOLOGY/Relief sewer eases overflow problem
Montgomery County, Ohio, experienced difficulty with sewer overflows at the Holes Creek Drainage Basin because of development in the surrounding area. “The pipes just weren’t big enough to handle the flow,” says Terry Dalrymple, chief engineer for the county. To combat the overflow, the county decided last spring to start planning a relief sewer system.
When Montgomery County planned the Holes Creek Tunnel Project, the design called for open-cut construction with alternate routing to avoid depths exceeding 25 feet. However, several obstacles impeded open-cut installation. For example, some locations had depths exceeding 30 feet; the pipeline crossed underground and overhead utilities; and crews would not be able to close down heavily used roads near the construction. Additionally, environmental concerns were raised because the pipe passed through wooded areas.
Using microtunneling, the county installed 1,085 feet of 36-inch fiberglass reinforced polymer mortar 300-ton jacking pipe and seven tunnels using 3,268 feet of the same type of 48-inch, 400-ton pipe. The pipe was furnished in 10-foot sections with push-together, flush, gasket-sealed joints. Hobas Pipe, Houston, made the pipe; Dayton, Ohio-based Wool-pert provided engineering services; and Bowen Engineering, Fishers, Ind., performed the installation. The $3.8 million project required 10 tunnels and was completed in just over a year. The new tunnels will serve as a relief system for the county when they are connected with another expansion scheduled for completion in 2001.