Uplift performance of transmission tower foundations embedded in clay

The contribution to the uplift stiffness and capacity provided by the clay beneath the base of shallow footings typical in configuration to those employed to support high voltage electricity transmission towers is examined. Pore pressures developed at the base of appropriately scaled footings founded on clay were measured over a wide range of uplift rates in a geotechnical centrifuge. These measurements, coupled with data from tests on identical footings founded on sand, are used to provide insights into the influence of uplift rate on the failure mechanism and footing capacity. Data from a series of undrained triaxial extension tests, conducted over a range of strain rates, are presented and these data combined with finite element back-analyses of the centrifuge uplift tests are used to provide designers with a means of assessing the capacity and load-displacement response of footings on clay subjected to high rates of uplift in service.