Design and Construction of Deep Foundations to Support Electric System Transmission Lines State of the Practice-PDF

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The Deep Foundations Institute’s 2025 report reviews current practice in designing and constructing foundations for electric transmission lines. Because the industry lacks a unified foundation code or comprehensive guidance, practices vary widely among utilities, even under similar conditions.<br /><br />The report surveys foundation options, including drilled shafts, direct-embedded poles, micropiles, helical and driven piles, augered cast-in-place piles, rock anchors, grillages, and spread footings. It also examines structural and environmental loads; performance and movement criteria; geotechnical investigations and design properties; analysis models; construction, testing, and quality control; and site influences such as scour, slopes, excavations, groundwater, corrosion, and liquefaction.<br /><br />Key shortcomings include inconsistent design methods and safety or resistance factors, limited coordination between structural and geotechnical design, uneven subsurface investigation practices, and uncertainty about acceptable settlement, rotation, and deflection. Environmental hazards and construction-related loads are often not addressed consistently, while foundation testing and quality assurance lack standard protocols. These inconsistencies can lead either to excessive conservatism and higher costs or to uneven reliability.<br /><br />The committee recommends developing industry-wide guidance that clarifies which design models suit particular foundations and conditions; establishes consistent strength and service load cases, limit states, and movement criteria; and provides coordinated approaches for both allowable-stress and reliability-based design. It also calls for guidance on site investigations, geotechnical property selection, environmental effects, concrete detailing, corrosion protection, testing, and construction QA/QC.<br /><br />The publication documents the state of practice rather than prescribing a standard. Its purpose is to provide a shared technical foundation for future consensus guidelines and standards, improving consistency, safety, reliability, and economy across transmission-line foundation projects.

Keywords

electric transmission lines

foundation design

geotechnical investigation

drilled shafts

direct-embedded poles

micropiles

helical piles

load criteria

quality control

corrosion protection