Each manhole was manufactured to the precise miter necessary for its position as the pipeline followed the meandering creek.
Click here to enlarge imageProject specifications included 8,000 feet of pipe – 2,100 feet of 48 inch, 3,700 feet of 60 inch and 2,200 feet of 66 inch. The alternatives were profile wall polyethylene and centrifugally cast, fiberglass-reinforced, polymer mortar (Hobas CCFRPM) pipe. Neither of these is affected by hydrogen sulfide.
High Stiffness Design
The contractor, John L. Jersey & Son, Inc. of Portland, OR, bid the job with Hobas CCFRPM pipes. John F. Kalkhoven, P.E., Jersey project manager, said that strength and durability were two of the important reasons his firm chose the pipe. He explained that the profile wall polyethylene was not as stiff as the Hobas product and it would require additional care to insure a quality installation.
"The polyethylene pipe would have required a filter cloth liner for the excavation and complete coverage with bedding rock," he said.
The CCFRPM pipe's trench did not require filter fabric and needed bedding only up to the springline.
"Jersey & Son told Clean Water Services' staff during an interview that Hobas pipe would cost less than the profile wall option to install and would make installation easier," Lampert said.
Fiberglass System
In order to accommodate the many changes on the sewer line as it followed the meandering creek, Jersey installed manholes. It wasn't uncommon to have a series of manhole runs of only 100 feet, 70 feet, 130 feet then 500 feet.
"The custom-made manholes simplified this task," Kalkhoven said.
Hobas manufactured each manhole with the correct miter and FWC couplings so that they were easily joined.