A major purpose of overhead transmission line design is to achieve a minimum cost for a given level of reliability and safety. The greatest uncertainty in this process is in foundation design. The Electric Power Research Institute (EPRI) has sponsored, since 1977, a comprehensive program of activities in foundation design. A recent activity involves performing well documented load tests of foundations partially or totally socketed in rock. As part of this activity four full-scale foundations were tested. All four foundations, two reinforced concrete drilled shafts and two directly embedded steel poles, were subject to high moment loads and modest shear and compression forces-loads which are characteristic of single pole transmission line structures. The load tests performed, data collected during the field exploration and laboratory testing, and predictions using the available analytical models are presented. Comparison of test results and model predictions indicates a need to refine presently available design methods.
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