Analytical solution for negative skin friction of single pile based on effective stress method

The calculation method for negative skin friction of a single pile has not been unified yet. To improve the design and calculation level of the single pile under vertical load considering negative skin friction, the threshold limit value of pile skin friction was determined based on the effective stress method. The effects of relative displacement of pile-soil and pile depth on pile skin friction were analyzed, and a nonlinear calculation model for pile skin friction was established. The pile skin friction was divided into elastic and plastic states. In the elastic range, the friction is a quadratic function with the depth of the pile body; while in the plastic range, the friction is distributed linearly along the pile body, and the slope is the product of the effective weight of the soil around the pile and the negative friction coefficient. Consequently, the analytical solution of the pile skin friction for the corresponding pile section was acquired. Based on the theory of pile axial force calculation, a formula for calculating the axial force of a single pile under different distribution forms of pile lateral friction was obtained. The reliability, applicability, and practicality of this model were verified by measured data. Based on the calculated pile shaft axial force, the axial force of single pile with different distributions of skin friction was analyzed. This study has practical significance for fully utilizing the performance of pile foundations and improving the level of pile foundation design.