The pipe was designed with a stiffness class of 46 pounds per square inch (psi) to meet structural requirements. “The ASTM standards require the pipe manufacturer to run the product line through a variety of factory tests including, in this case, ASTM D4161, Standard Specification for Fiberglass Pipe Joints,” says Truong Do, process quality control, Hobas Pipe. “Hobas performed this test on low profile bell pipe joints of this configuration at a test pressure of 50 psi, well above the anticipated operating pressure of the gravity pipeline.”
Once the pipe was delivered, Michels used an industrial tow tractor – or tugger – to pull it through the sewer and a skid steer to follow and assist in pushing, setting in place and final blocking. The pipe was installed in only four runs – ranging from 267 feet to 1,372 feet – through three manholes and two shafts used to drop materials down into the sewer pipes. The installation occurred in a live sewer tunnel, but the water was only six to 12 inches deep, says Russ Pollard, project manager at Michels Corporation.
After installation, grouting was added to fill the annular (ring-shaped) space between the existing pipe and the new fiberglass pipe. This increases the life of the pipeline and reduces the possibility of collapse as the original host pipe weakens.
“Due to the size of the pipe, it was a little more cumbersome than smaller diameter pipe, but once we developed a safe procedure and system of installation, the install went smoothly,” says Pollard. Milwaukee plans to evaluate its remaining original sewer pipes in the next few years for potential rehabilitation.