Study on the calculation method of negative skin friction for end-bearing piles based on soil deformation

The application of a significant additional load induces soil deformation around the pile, generating a downward drag force, commonly referred to as negative skin friction. This phenomenon significantly reduces the pile's ultimate axial load capacity. Therefore, precise estimation of negative skin friction is crucial for pile design. To accurately calculate the negative skin friction acting on the pile, it is essential to determine the stress states at the pile-soil interface under varying soil deformations. However, many existing methodologies solely consider peak or residual stresses on the shear plane, neglecting the process of stress changes in soil deformation. This approach often results in an overestimation of negative skin friction. In this investigation, we propose a novel method for calculating negative skin friction that comprehensively accounts for the whole process of stress state alterations occurring during soil deformation (pre-failure zone and peak stress, post-failure zone and residual stress state) and describes the relationship between soil deformation and stress using a hyperbolic mechanical model. On this basis, soil deformation behavior is classified into three distinct forms. The spatial distribution characteristics for negative skin friction were then explored individually for each form. Additionally, the influence of different soil parameters on the spatial distribution of negative skin friction was also investigated. Finally, the accuracy and applicability of the new negative skin friction calculation method is validated through comparison with field measurement data. It can be used as a reference for practical engineering.