- ENGINEERING INFO
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Historically, water utilities have used mechanical restraining harnesses when bell-and-spigot PVC pipe joints must be restrained to resist axial thrust forces. The need for restrained joints in pipeline design is typically driven by the presence of fittings and valves, significant elevation changes, higher surge conditions, or unstable soils. In most direct bury projects only certain sections of a pipeline require restrained joints, while some projects require most, or all, of the pipeline to be fully restrained.
With the development and growth of Fusible PVC® pipe technology over the last decade the waterworks industry now has a cost saving alternative to mechanical restraining harnesses for direct bury, restrainedjoint, PVC pipeline design and construction. Forty or 45 foot lengths of Fusible PVC® pipe joined by thermal butt fusion are now being cost effectively employed as an alternative to gasketed PVC joints secured with metallic restraining hardware every twenty feet. A leak-free, fully restrained section of pipe pre-fused outside the trench is often less expensive and quicker to install compared with assembling mechanical restraining harnesses after each length of bell-and-spigot PVC pipe is laid in the trench.
The advantages of a fused, restrained pipe system are particularly beneficial in the presence of corrosive soils, where metallic restraints often require significant additional treatment and protection to prevent corrosion. In addition, fused joints provide resistance to both axial and lateral forces, providing further pipeline protection in alignments with unstable soils. Fused PVC pipe sections can easily transition to belland- spigot PVC pipe due to material and dimensional compatibility.
Use of metallic restraining harnesses in highly corrosive soils typically requires one or more of the following mitigation steps: 1) special construction materials (stainless steel restraining hardware), 2) extensive coating and tape wrap protection of the restraining mechanism and hardware, or 3) a cathodic protection system to prevent the hot soils from rendering the metallic restraining harnesses and hardware all but useless in just a few short years.
|Pipeline Details and Project Summary|
|Project:||Chilled Water Main|
|Location:||Mount Vernon, IN|
|Pipe Size:||24” & 20” DR18 Fusible PVC® pipe|
|Contractor:||Blankenberger Brothers Inc.|
A recent example of this application was successfully demonstrated on a project in Mount Vernon, Indiana for the installation of a 20-inch and 24-inch diameter chilled water main for a large industrial customer. The customer required a new, fully restrained pipeline to be installed in an area with highly corrosive soils. The USDA soils corrosion map below details the high level of corrosive soils (depicted in red) present throughout the pipeline alignment.
The engineer and contractor on the project were searching for alternate solutions to the use of conventional bell-and-spigot PVC restraining harnesses in order to generate cost savings, reduce construction time, and provide a longer-life pipe system. Their solution was to utilize 20-inch and 24-inch Fusible PVC® pipe fused into long lengths beside the trench. Pipe strings were then placed into the trench with excavators. The fused-joint PVC approach lowered material costs and produced meaningful “in trench” labor savings by eliminating the time-consuming assembly and protection of bell restraints.
Eliminating mechanical restraints, minimizing corrosion concerns, and reducing potential leaks is expected to significantly enhance the life of the water main. Improving the useful life of the pipeline, while saving time and money upfront, created a winning scenario for the owner, engineer, and contractor.