Abstract:
Non-tangent transmission line poles (“angle†and “dead-endâ€) often result in extremely large lateral forces which are transferred to the foundations. Many modern high voltage transmission corridor designs and ROW limitations promote the use of single support poles (monopoles) and preclude the use of guy anchors. These situations result in large foundation reactions and, accordingly, large foundations, typically drilled shafts. Because a portion of these reactions are unilateral, an offsetting unilateral foundation augment can be utilized to reduce the net sum of the forces. After a careful study of the transmission pole anchorage, available right(s) of way, soil conditions, and various load cases and reactions in a pilot case, an efficient foundation was designed and constructed utilizing two inclined earth anchors (“tiebacksâ€) attached to a single drilled shaft with reinforced concrete corbels to offset the unidirectional forces. This design has since been utilized for 13 foundation locations. The design and construction lessons learned demonstrate how the foundation for an angle or dead-end transmission line pole can be reduced in size and construction cost through the use of an inclined earth anchor foundation. Conditions which support the use of inclined earth anchors and those which may preclude their use are discussed.