AEP 765 kV Transmission Line: Uplift Capacity of Shallow Foundations on Sloping Ground

Abstract

Shallow foundations placed in sloping ground have less uplift capacity than the same foundations built on flat ground, if the uplift load has a horizontal component toward the downward slope. Since the depth of transmission line foundations to resist uplift loads is usually determined for level ground, maintaining this depth in sloping ground could result in insufficient uplift capacity. Common sense dictates that to achieve an uplift capacity in sloping ground commensurate with the level ground capacity, additional embedment of the foundation is required. The effect of sloping ground on the bearing capacity of shallow foundations is addressed in the technical literature. However, to the knowledge of the authors, no guidance is provided in the technical literature to determine the increased depth. This paper presents an analytical method to estimate the increased depth required for foundations in sloping ground to match the level ground uplift capacity. The procedure is based on changes resulting from the sloping ground in the active and passive pressures on the sides of the soil prism above the foundation. This approach is used to derive simple equations for the required increased depth.