- ENGINEERING INFO
- CASE STUDIES
Sunset Beach, a coastal town halfway between Myrtle Beach, SC and Wilmington, NC that includes a small barrier island, consummated an agreement with Brunswick County in 2006 to construct a wastewater collection system that would serve the areas within Sunset Beach without sewer service. One of the challenges would be to cross the Intracoastal Waterway and a salt marsh with a force main capable of operating in a harsh, corrosive environment for both the interior and exterior of the pipeline. Brunswick County, the entity responsible for managing the project, hired URS Corporation in Raleigh, NC to advise on possible methods of construction and materials available for the 4,200 LF crossing.
URS concluded that a horizontal directional drill installation would be the best option, and proposed UGSI's Fusible PVC™ pipe be utilized as the base bid product. For competition, URS also included an upsized HDPE main, but encased in a 16" welded steel casing. The casing was considered necessary to avoid overstressing and stretching the softer (lower modulus) HDPE during the long duration pullback. Ultimately, the HDPE/steel casing option was deemed uneconomical, and 10" DR14 FPVC® pipe was chosen for the project.
A complication arose as NCDOT required material approval for Fusible PVC® pipe. Although testing and pilot projects were underway, NCDOT required a special waiver to deploy the material on such a long crossing. After several meetings and solid references were brought to NCDOT's attention, NCDOT did approve FPVC® pipe for the installation. URS's Randy Foulke notes, "NCDOT's initial reservations caused some delays, but once we laid out all the engineering reasons that this was our best option, they issued the encroachment agreement. Ironically, not too long afterward NCDOT issued a general approval for Fusible PVC® pipe within its rights-of-way. I think the project team's efforts may have helped them reach that conclusion."
|Pipeline Details and Project Summary|
|Project:||Sunset Beach Intracoastal Crossing|
|Length & Diameter:||4200 LF of 10" DR14 FPVC®|
|Pressure Test:||150 psi for 2 hours|
|Intermediate Fusion:||9 fusions over 17 hour pullback|
|General Contractor:||Ralph Hodge Construction|
|HDD Subcontractor:||Environmental Crossings, Inc.|
|Owner:||Brunswick County, NC|
Ralph Hodge Construction won the bid and hired Environmental Crossings, Inc. (ECI) to drill and pull back the 10" FPVC® pipe. UGSI mobilized to fuse pipe in January 2011, but was restricted to an area only allowing about 400 LF fused sections. Once ECI had completed the pilot hole and first reaming pass, UGSI again mobilized to fuse intermediate joints during pullback.
ECI's pilot drill followed a bore path with two horizontal curves and a depth exceeding 65' before exiting on-point 4200 LF from the entrance location. With assistance from Ralph Hodge, UGSI positioned and fused the 10 strings of pipe, one after the other, as the pullback proceeded. Due to a quality borehole and water ballasting, pullback forces averaged less than 20,000 pounds and never exceeded 35,000 pounds; less than half the rated allowable strength of the 10" FPVC® pipe. Bruce Brasher of ECI was pleased: "This was our first attempt with Underground Solutions' product and we were quite pleased with their performance. We are happy to add this project to our resume and look forward to more opportunities with Fusible PVC® pipe."