Wolf Bay Crossing Project
PowerSouth’s Wolf Bay Crossing Project in Orange Beach, Ala., is a multi-faceted example of challenges and innovation in HDD and complex installation of large-scale underground electrical transmission lines subject to specifically engineered thermal grout requirements. The installation — which is now the longest of its kind in the United States — doubled the record of thermal grout used in conjunction with HDD and had the longest length of continuous cross-linked polyethylene insulated (XLPE) cable rated at 115-121kV and 300MVA. The installation involved approximately 6,200 ft of 36-in. diameter steel casing pipe installed by HDD pilot hole intersect and HDD-assist methods under Wolf Bay in Alabama. This included crossing under an intracoastal waterway channel while reaching depths of up to 110 ft. Approximately 220 ft of 60 in. conductor casing was used to protect the active substation at the southern end of the crossing from impacts of the HDD process. A 36-in. diameter steel casing pipe was installed by HDD throughout the 6,200-ft long crossing. Once the 36-in. steel casing was installed, multiple HDPE pipes were bundled and pulled together into the casing with stainless steel bands spaced throughout the length of the bundle. Before the cable was installed, a completed bore path profile was generated and used in developing a strategy for the thermal grout operation in order to fill the extraordinary length and volume of fill specified by design requirements. Thermal grout is installed around underground conduits to remove heat caused by high voltage power transmission.
Project Owner: PowerSouth Energy Cooperative
Engineer: Waldemar S. Nelson and Co.
Contractor: Southeast Directional Drilling
Shively Interceptor Project
The Shively Interceptor Project in Shively, Ky., is the third largest pilot tube microtunnel (PTM) project ever completed in the United States, and arguably the most challenging. The project consisted of the installation of more than 10,678 lf of vitrified clay pipe (VCP) with a total grade change of less than 13 vf over the entire alignment. The breakdown of footage by diameter is as follows: 1,228 lf of 27-in VCP, 733 lf of 21-in. VCP, 4,280 lf of 18-in. VCP, and 4,437 lf of 15-in. VCP. The trenchless crossings required (three each) 12 ft-diameter shafts ( two – secant pile, one – internally braced sheet pile cell), and (34 each) 9-ft diameter shafts ranging from 17 to 35 ft deep. The soil conditions consisted of loose, medium dense, coarse sands below the water table to loose, fine sand above the water table. The PTM method was the only choice for installation of this sanitary sewer pipeline. The extreme depths, soil conditions and extremely flat design grades would have made an open-cut installation of this sanitary sewer in the middle of a tight residential area nearly impossible and would have had a severe impact on the residents of Shively. The specified approach of PTM saved Louisville MSD a substantial amount of taxpayer dollars and allowed the residents of Shively to maintain their day to day lives with minimal impact.
Project Owner: Louisville MSD
Engineer: Louisville MSD
Contractor: Midwest Mole