Design of Helical Pile Groups for Support of Electric Power Structures

Foundation designs utilizing helical pile groups are increasingly widespread in the electric power utility industry. Yet the application of these systems lacks uniformity and knowledge gaps may exist. Recently, a body of codes and practice documents have been prepared by DFI and ASCE subcommittees regarding standard practice for electric power transmission structures design. These codes and standards are discussed as they apply to helical pile groups. With a better understanding of how the codes apply to these foundation types, engineers and designers can more confidently and adeptly specify and bid from a broader range of deep foundation options. Design of electric power transmission structures is most challenging at angles, water crossings, and dead ends. These structures often are characterized by large overturning moments. This presentation will cover simple hand calculations for estimating the distribution of pile reactions from ground line tower moments. Then, pile groups modeling using Ensoft® Group will also be covered in depth and with specific design examples from real case histories. Design considerations for sizing of individual piles and key differences between pile design for building structures and pile design for power transmission towers and applicable codes and standards will be discussed. Preliminary findings from field measurements performed on existing helical pile group supported structures, if available, may be included as they relate to validation of models.