PVC Overcomes Corrosive Soils and Restrained Pipe Length Demands for Open Cut and Trenchless Installations

The City of Fayetteville, Arkansas is a densely populated urban area located in the Northwest corner of the state. Situated within the Ozark Mountains and known for picturesque landscapes, winding rivers and scenic lakes, these attractions make it one of the nation’s top 100 fastest growing cities. With a population of just over 100,000 and rising, the state has planned several roadway expansions and interchange projects to better improve the flow of traffic in the area. In one of these projects, the Arkansas Department of Transportation has proposed plans for a future overpass and a new roadway extension of 15th Street providing improved movement of traffic by connecting frontage roads South Futrall Drive and South Shiloh Drive. To support this construction, a new watermain is required in an alternate location to better align with the new roadway. The new proposed watermain posed several challenges in design:

• Project Location: Construction along the busy Interstate 49 required diligent design to ensure safety and reliability.
• Soil Properties: Known corrosive soils in the area required the engineer to choose a product that was resistant to these conditions.
• Environment: The proposed watermain alignment meanders and crosses the Town Branch Creek, providing concerns with floodwater and washout warranting a fully restrained system.
• Restrained Length: The extensive restrained length requirements made material selection key to maintain an efficient, constructible and long-lasting system given soil properties. 

The project required the construction of a new 2,200 LF 18-in. PVC watermain to replace the existing 24-in. ductile iron watermain. The replacement was due to a required changed alignment for the 15th Street overpass proposed by the Arkansas Department of Transportation. With the proposed alignment shifted to cross under a narrower portion of 15th Street, the new watermain followed along the Town Branch Creek roughly parallel to Interstate 49 then crossed the creek proceeding under 15th Street through casing installed by auger bore and open cut. The design engineer, Hawkins-Weir Engineers Inc.,  was able to downsize the watermain to better suit current capacity requirements of the service area.

The pipe utilized for the project was approximately 2,200 LF of 18-in. AquaSpring® C900 Certa-Lok® RJIB, DR18 PVC pipe offering the required restraint, design life, corrosion resistance, and appropriate delivery timeline required for the project.

The 36-in. steel encasement required for the proposed 15th Street cross section was installed partially by open cut under the future roadway.  The encasement extended just past the proposed mechanically stabilized earth (MSE) wall and, by auger bore, underneath the Town Branch Creek, connecting the two casing sections. Restrained pipe was required through the encased sections but was also required by the engineer for the direct bury to protect the integrity of the watermain in case of creek flooding given the alignments close proximity. With a three-person crew, Nabholz Construction achieved trouble-free and timely installations. Despite the large diameter size, joints were assembled in minutes, providing a bidirectional, fully restrained system. The crew utilized a spline insertion tool provided by Westlake Pipe & Fittings to streamline the process; one crew member in the trench to properly align the spline, and another at the top of trench driving the spline in. “The Certa-Lok® pipe is easy to install and provides a benefit for a faster installation,” said Oren Noble, P.E., with Hawkins-Weir Engineers, Inc. “The contractor was not familiar with the pipe and the installation of the spline but quickly learned the technique for installation. The contractor was provided on site instruction and didn’t use any lubricant for the spline.”  Nabholz also noted the ease of assembly, even in an open trench scenario. They stated that for casing applications, this is the best solution available. With 360 ft of casing, a substantial amount of time and effort was saved utilizing Certa-Lok as the carrier pipe compared to other external restraint systems. Crews were able to work efficiently to successfully complete the watermain.