The calculation of negative friction on pile foundation by effective stress iterative method

The effective stress iterative method of estimating neutral point and downdrag on a single pile was presented in this paper.A case was introduced to illustrate the trial-and-error procedure.By comparing the calculation result with the field measured value,effective stress iterative method is verified to be simple and practical and can be used in pile foundation design.Axial force of pile above the neutral point calculated by the presented method have differences from field measured value.The main cause lies in that the assumed negative skin friction is different from that of the field.