The role of soil constitutive modelling on the assessment of seismic performance of caisson foundations

In this paper, the influence of inelastic soil behaviour on the seismic performance of bridge piers supported by caisson foundations is assessed. The results of an extensive parametric study, performed assuming a linear elastic and an elastic-plastic soil behaviour, are compared, showing the strong influence of the inelastic soil response. The geometrical properties of caissons and piers are varied; the systems are subjected to seismic records capable of mobilising the shear strength of the soil. 3D dynamic analyses are performed in the time domain and in terms of effective stresses but assuming undrained conditions. The role of soil constitutive modelling is assessed by comparing the deck drift and the forces transmitted by the superstructure to the caissons, both computed under the assumption of linear elastic and elastic-plastic soil behaviour. The results clearly indicate for which systems the linear elastic assumption is satisfactory and when, conversely, soil non-linearities should be considered.