Analytic method for passive piles considering excavation-induced unloading effects and deformation coupling effect

Excavation of foundation pits and tunnels will inevitably influence the working performance of adjacent loading piles, thus, it is important to accurately evaluate the additional pile responses due to soil excavation. In order to overcome the deficiency of the conventional Winkler’s foundation beam model, a modified nonlinear two-stage analysis method is proposed. It can consider the nonlinear characteristics of pile-soil interaction, influence of pre-phase working load on the excavation-induced additional axial force as well as influence of axial force on the lateral deflection more factually. Combined with the incremental method, the solving process of nonlinear equations is then presented. Moreover, the calculated results are compared with those from other existing methods to verify the calculation accuracy of the proposed method, and a further study is made to investigate the influence laws of pre-phase working load on additional axial force and the axial force on lateral deflection. The results indicate that the influence of pre-phase working load on the vertical additional responses is significant; the influence degree of axial force on lateral responses is relevant to (but not limited to) the mode of free-field displacement, and under some situations, the influence of axial force on lateral responses is not negligible and the coupling effects should be rationally considered.