Numerical back-analysis of dynamic centrifuge tests on the seismic behaviour of caisson foundations supporting bridge piers

Over the last few years, an ever-increasing interest on a sort of a “Reversed” Capacity Design of geotechnical systems has been emerging, particularly when looking at the seismic design of bridge foundations, such as shallow, piled and caisson foundations. In this approach, soil irreversible behaviour is triggered on purpose during strong seismic events, so as to protect the superstructure. Although the capacity of soil-caisson systems is quite high if compared to shallow and piled foundations, limit conditions of these systems may be actually attained during destructive seismic events. The above-mentioned framework boosted the research on the dynamic response and interaction diagrams (i.e., failure envelopes) of rigid and massive caisson foundations [1][2]. Gaudio et al. [3] recently performed an experimental campaign via dynamic centrifuge tests, where a typical layout of a cylindrical caisson supporting a bridge pier was subjected to a series of ground motions. The caisson was embedded in a typical alluvial deposit, where the clay stratum was either soft and very soft. In this paper, the results of preliminary 3D Finite Element back-analyses reproducing the centrifuge test are presented and discussed, for the specific soft-clay case. The analysis first aimed at reproducing and then extending the experimental investigation, so as to both validate and better understand the phenomena observed in the centrifuge. It is shown that, even with a simple but still comprehensive calibration of handy soil constitutive models, the main features ruling the seismic performance of the systems at hand can be fairly captured.