Nonlinear soil-pile interaction induced by ground settlements: pile displacements and internal forces

In urban areas, the construction of tunnels and deep-excavations beneath and near to pile foundations can be detrimental for the superstructure and the foundation. A two-stage continuum-based nonlinear soil-pile interaction model is presented in this paper for predicting the axial and flexural response of piles affected by ground movements. The model accounts for the effects of near-pile non-linear (hyperbolic) soil stiffness degradation and unloading effects. The approach is used to analyse the relationship between the pile axial response (both displacements and internal forces) and greenfield ground settlements for purely-frictional and floating piles in uniform ground. Both displacement and non-displacement piles are analysed by applying appropriate pre-excavation loading sequences. Results demonstrate the influence of initial safety factor, installation method, and capacity distribution (between shaft and base) on pile settlements and on critical tensile axial forces (both in terms of magnitude and depth). Dimensionless design charts are provided to estimate pile settlements and critical axial forces for the case of greenfield settlements that either increase or decrease linearly with depth. These charts provide a rational and more general framework to describe excavation-induced effects on piles than empirical methods.