Calculation of displacement and ultimate uplift capacity of tension piles

Tension piles are widely used for resisting the uplift loads of underground structures such as deep basements and underground transformer substation, and as foundations for tall buildings subjected to high bending moments. Based on the axial Winkler foundation model, both elastic closed form solutions and elasto-plastic solutions using a unified ultimate skin friction along pile shaft in conjunction with finite difference methods are presented in this paper. Accordingly, a spreadsheet program is developed. Using these solutions and the program, displacement and ultimate uplift capacity of tension piles are examined in detail; effects of modulus of subgrade reaction ks for the Winkler model, unified ultimate skin friction coefficients Nc, αs, n and excavation depth on pile displacement and ultimate uplift capacity are investigated. It is indicated that the values of Nc and Kc have a significant influence on the displacement, while the uplift capacity of tension piles is dominated by values of Nc and overburden stress.