Individual joint air tests were conducted at each joint to an air pressure of 3.5 pounds per square inch.
“The project was designed to relocate the new Outfall Trunk Sewer a distance away from the existing line,” said Mark Cotter, P.E., director of Public Works, City of Sioux Falls. “The old line is essentially next to the Big Sioux River. As a result of this close proximity to the river, as the pipe and joints deteriorated and the river was running high, it would take on additional inflow/infiltration. For this reason, we moved the new line as far from the river as we logistically could. The new alignment will also give us better access to the line in the future.” With limited access to the existing line, repairs were extremely limited. The old line will be decommissioned after the new outfall is put into service. Reliable replacement Replacement of the Outfall Trunk Sewer consisted of approximately 9,700 linear feet of pipe. Hobas supplied 8,500 feet of 72-inch cen- trifugally cast, fiberglass-reinforced, polymer mortar (CCFRPM) pipe that was installed by open cut. Included in the project was 505 feet of 72-inch CCFRPM jacking pipe that was utilized on two crossings — beneath Cliff Avenue and Interstate 229. The South Dakota Depart- ment of Transportation reviewed and approved the use of the installa- tion method as well as the pipe materials. “The remaining length of pipe was smaller-diameter pipe connecting to the city’s equalization basins, and the installation of an additional siphon pipe under the Big Sioux River. There are several hundred addi- tional feet of smaller-diameter lateral connections as well,” Cotter said. After the pipe was installed, the required tests and inspections were performed. “Individual joint air tests were conducted at each individual joint to an air pressure of 3.5 pounds per square inch,” Posten said. “A mandrel test was performed through the entire line to test for out- of-roundness or deflection after backfilling was complete. Finally, we performed a closed-circuit video inspection through the entire line as a final inspection for leaks or defects and to document pre-operation conditions.”
All tests were satisfactory, but the video inspection did reveal one joint that was leaking groundwater prior to being put into service. This joint was repaired in place by Hobas Field Services by injecting a grout product through the pipe wall on each side of the joint to stop the leak. Once the joint was sealed on the exterior, the interior side of the joint was filled with resin putty and sanded. Finally, fiberglass lamination sheets were layered over the joint and injection holes to completely seal the joint. Re-inspection found the joint to be water tight. Restoring structural integrity The new 72-inch Outfall Trunk Sewer allows for continued population growth and increases the overall capacity of the city’s sewer system by approximately 21 million gallons per day, which will reduce the risk of backups and sewer overflows. The new 72-inch outfall project is the last phase of a major replacement project of the city’s main trunk sewer that included four separate segments of the Central Main and three separate segments of the Sioux River South Interceptor sewers along the Big Sioux River, varying from 36- to 60-inch pipes. Construction took approximately 16 months from start to completion. The contractor, H&W Contracting, LLC of Sioux Falls, has success- fully completed numerous water main, sanitary sewer, and storm sewer projects for the City of Sioux Falls and surrounding municipalities in the four-state area. The Sioux Falls Water Reclamation Division continues to develop and improve the city’s infrastructure. During 2016-2017, the city expected to complete a Water Reclamation and Collection System Master Plan that will assist with planning for the next 20 to 100 years.
ERIN BOUDREAUX is marketing manager with Hobas Pipe USA (www.hobas.com).
40
csengineermag.com
july 2018
Made with FlippingBook Annual report