Analysis of excavation-induced responses of loaded pile foundations considering unloading effect

In urban areas, the excavation of tunnels and foundation pits will inevitably influence the working performance of adjacent pile foundations, and many failure cases have been reported in recent years. Thus, it is important to accurately evaluate the additional pile responses. Most existing methods tend to neglect the influence of working load on excavation-induced additional pile responses, and some of them cannot properly consider the nonlinear characteristics of pile–soil interaction. In this paper, governing differential equations, which take the coupling effect of longitudinal and lateral deformation into account, are established for both single piles and pile groups. A new theoretical method, in which the deflection curves of the enclosure structure calculated by the modified “m” method are taken as basic calculating data, is developed to estimate the free-field soil movements induced by foundation pit excavation. A two-stage analysis method is then proposed to study the behavior of pile foundations subjected to excavation-induced ground movements. This method can take the influence of working loads acting on pile heads into account, and overcome some deficiencies of existing methods. Then, the proposed method is verified by comparing the calculated results with boundary element solutions and centrifuge test data. Good agreements between these solutions are demonstrated. Thereafter, this method is employed to study the influence of the vertical working load on the excavation-induced pile responses. It can be found that the influence of the vertical working load on the vertical pile responses is significant, and under some special situations, the influence of axial force on lateral responses is not negligible and the coupling effect should be factually considered.