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CIPP Project Requires Complex, Challenging Bypass Pumping Plan
An essential element in many projects to rehabilitate buried pipe is the design and construction of a bypass system to carry flow during the period the segment being restored is out of service.
In many instances, design and installation of the bypass is just as complex as the job of rehabilitating the pipe.
A recent example is the bypass needed for cured-in-place pipe (CIPP) lining that involved 6,100 feet of 54-inch diameter reinforced concrete sewer pipe for a project for Jefferson County, AL.
To accommodate required daily flow rates, the bypass system required five runs of 18-inch HDPE pipe totaling 18,500 feet and six 18-inch Sunbelt Quiet Flow pumps.
The project owner was the Jefferson County Commission. Prime contractor was Layne Inliner, Sunbelt Rentals was the contractor for the bypass system and CH2MHill was the project engineer.
“The project involved one of the largest lining projects in recent years for Jefferson County,” said Ladd Gould, Sunbelt national strategic account manager. “The size and magnitude of the bypass made for one of Sunbelt Rental’s more challenging bypass installations.”
To eliminate the additional cost of bypass relocation, the system was designed to bypass the entire work area -- just over 7,800 feet, said Gould.
“In order to achieve the specified flow of 40-million gallons per day (mgd),” he explained, “Sunbelt concluded that five runs of 18-inch HDPE were necessary to reduce the total dynamic head on the bypass system. This design required the installation of 38,500 feet of 18-inch diameter HDPE pipe. Constructing the full-length bypass also reduced the expense of placing additional suction structures on the sewer.”
The project plan did not specify the route of the bypass leaving Sunbelt with the responsibility of selecting the best route for the five runs of pipe.
“As it happened,” Gould continued, “there was a drainage canal that ran through the town of Bessemer where the pipes could be placed which greatly reduced the bypass impact on the area by avoiding road closures, traffic control, trenching and property restoration.”
Suction structures were installed upstream from the starting point of the lining on the existing 72-inch sewer that fed the 54-inch pipe. Because of the depth of the sewer and volume of sewage that was required to be bypassed, three new structures were “dog housed” on top of the 72-inch sewer for suction access.