The ultimate shaft resistance of uplift pile is divided into two parts

one is the setting strength of pile and soil

which is irrelevant to the earth pressure of pile

and the other is the force of friction

which is proportional to the earth pressure of pile and can be calculated using the friction law. With assumption of elastic soil

this paper studies the pile-soil interaction through the integral calculation using Mindlin formulation. Pile-soil interface displacement coordinate equation is derived based on the solution of cavity expansion in infinite soil. Then a limit state equation of uplift piles and its solution are presented. The methods for determining the parameters of soil and pile are also given. The equation can be used to calculate ultimate bearing capacity of uplift piles with considering the influence of such factors as pile and soil materials

pile length

pile diameter

depth of pile top

group piles effects

unloading effect due to excavation

and so on. As an example

a full-scale test was performed on a large steel pipe pile with a length of 81.3m

a diameter of 1.7 m and a wall thickness of 25mm. The calculated and measured ultimate uplift bearing capacities are compared

showing that the proposed method for calculating the bearing capacity of uplift piles is satisfactory and applicable and has an accuracy much better than the methods recommended in the current codes of China.