Project Images Plains & Eastern Clean Line Substation Site Preparation Design, Permitting and Geotechnical Analysis Project Summary The Plains & Eastern Clean Line high-voltage direct current (HVDC) project originated from a need to carry renewable wind energy from the Great Plains east toward energy markets in need of clean energy. The 700-mile direct current transmission line has three key locations of AC/DC converter stations: one in Texas County, Oklahoma, at the beginning of the line; one in Shelby County, Tennessee, at the end of the line; and an intermediate delivery location in Pope County, Arkansas. Hanson provided an engineering review of geotechnical reports and foundation loads prepared by others for an HVDC converter station site in Shelby County. Based on this geotechnical review, Hanson also developed a site-specific seismic analysis for use in the station’s foundation design. As a result of the preliminary work’s success, Hanson was asked to provide site preparation design services for all converter station locations. This work included preliminary site layout and grading plans for more than 200 acres of substation footprint. Hanson also was engaged to assessment the permitting requirements at each of the three sites encompassing preconstruction, construction and post-construction phases. The project’s unique elements included the large size of sites, the schedule of the project and the specialized equipment for each site. Because of the complexity of the electrical equipment at the sites, each one had to be designed within small tolerances of grade variations. Hanson developed 3D design models of the site topography, manipulated proposed grades across the site to within these tolerances, and produced contours and digital foundation-reveal reports to verify the proposed design parameters. The 3D modeling of each site also allowed Hanson to quickly revise and update proposed grades, contours, alignments, profiles and cross sections in response to different parameters and conflicts that were identified throughout the design process. All of this work was accomplished at an accelerated pace to prepare for permitting and construction. To complete the project within the schedule, Hanson used multiple design teams to allow work to proceed concurrently on each site. This team approach promoted the sharing layout methods and design standards, as well as reviewing each team’s work to verify layout consistency between sites.