Improved uplift capacity design for overhead line equipment in granular soils

With the transition to greater use of renewable energy resources and the growing demand for electricity, countries such as the UK are seeing considerable investment, expansion and upgrading of their energy transmission infrastructure. Overhead line equipment structures in the UK typically have pad and column or pyramidal foundations, with the critical loading case being tensile uplift. The design of new foundations and reassessment of existing structures often relies on simplistic and conservative design approaches where efficient design is key to minimising material use and carbon dioxide footprint. Both centrifuge testing and three-dimensional finite-element analysis were used to investigate and verify more efficient uplift design procedures. In addition, a centrifuge modelling technique was used to investigate a more realistic construction procedure that incorporated soil backfilling as an improvement over wished-in-place simulation. This work has shown that current frustrum based methods are conservative and may lead to unnecessary upgrading of existing structures. Other empirically based approaches generally overpredict capacity by a significant amount and may be unsafe. Investigations of recently adopted design approaches where failure mechanisms were linked to the soil’s dilation angle yielded much better performance.