Study of Electric Transmission Line Deep Foundation Design

Electrical system transmission line structures are typically supported by deep foundations such as concrete drilled shafts, driven piles, micropiles, and helical piles. Although a number of industry guidelines describe the fundamental design principles and construction/installation procedures of these foundation types, there is no comprehensive electrical system guideline, which relates all the elements needed to properly characterize loads imposed by electrical structures and extreme environmental conditions on foundations. There is a lack of guidance on relating electrical system loads developed from various industry codes to foundations governed by traditional civil engineering design standards. A task force assembled by the Deep Foundation Institute has conducted a survey of utility design professional to assess the state of the practice for transmission structure foundation design. This survey, in conjunction with a thorough literature review, will be used to develop a guideline design document with recommendations for uniform analysis and design of electrical system deep foundations. This paper provides a summary of task force efforts to date and the initial industry survey results. Included are discussions of existing design and code documents as they relate to electric transmission line foundations, and elements needed in a guide document to improve the efficiency and reliability of electrical transmission line foundation design.