- ENGINEERING INFO
- CASE STUDIES
Several years ago the City of Corpus Christi, Texas contracted with Urban Engineering to evaluate the feasibility of installing a redundant potable water line beneath the Laguna Madre bay near the JFK Causeway leading to Padre Island. Padre Island is part of a barrier island complex off the Texas coastline stretching from Galveston to Brownsville. A portion of Padre Island is located within the City of Corpus Christi, with water supply to the island operated and maintained by the City. In 1968, a 24-inch steel water transmission main was constructed across the Laguna Madre. With the steel line nearing the end of its useful life, the City of Corpus Christi decided to construct a redundant water transmission main that could meet current and future water demands on the island. During the preliminary design phase the City decided to include an 8-inch gas line and a 4-inch communications conduit along the same alignment as the new water transmission main.
Urban Engineering worked with the Army Corp of Engineers to determine the optimal route for the pipeline. To minimize impact to the environment, they decided to locate the alignment on the south side of the causeway and to install the new pipeline using horizontal directional drilling (HDD) in combination with conventional trenching in other sections. HDD was used to span the two water crossings. The first HDD crossings of 18-inch Fusible C-905® pipe and 4-inch FPVC® conduit pipe were 850 feet each. Each line was drilled and pulled in separately. The two HDD crossings under the Laguna Madre were over 5,500 feet each, also installed separately. Bridges Specialties, the general contractor on the project, contracted with Mears Group to perform all of the drills.
Doug McMullan of Urban Engineering stated: “Several pipe materials were evaluated for use on this project, including PVC, HDPE, and welded steel pipe. Steel pipe required a cathodic protection system and expensive coatings to withstand the harsh marine environment and was not considered to be competitive with plastic pipe at the design size (18-inch). HDPE pipe was not sufficiently proven as a material for HDD installs of this distance. Pipe buoyancy was also an issue with HDPE pipe, requiring expensive pipe collars to keep the pipe from floating during installation via open trenching. Since a large portion of the smaller diameter pipe (less than 30-inch) installed by the City is PVC, Urban Engineering wanted to use a material that was compatible with the existing pipe in the City’s system. The 18-inch DR18 Fusible C-905® PVC pipe selected for the project fits with the City’s current distribution assets, is a material the City can easily maintain and operate using its existing equipment, does not require cathodic protection, and has been installed previously by HDD in projects of similar distance.”
|Pipeline Details and Project Summary|
|Project:||Padre Island Water Supply|
|Location:||Corpus Christi, TX|
|Pipe:||Single Pulls of 5,545 LF and 850 LF 18” DR18 Single Pulls of 5,535 LF and 850 LF of 4” DR14|
|Owner:||City of Corpus Christi, TX|
|Contractors:||Bridges Specialties (GC), Mears Group (HDD)|