Input of fully 3D FE soil-structure modelling to the operational analysis of jack-up structures

Jack-ups are mobile structures widely employed in the offshore industry as drilling rigs or installation/maintenance vessels (e.g. for offshore wind farms). To assure safety at each location, site-specific assessment is required to predict the performance of the unit during installation and operations. The response of jack-ups to environmental loads is highly affected by the interaction between all footings (spudcans) and the underlying soil, an interaction still challenging to describe under general 3D loading. This work emphasises the potential of 3D continuum simulations to capture non-linear soil-structural interaction in jack-up units. An integrated jack-up–spudcans-soil 3D finite element (FE) model is set up by including strain-hardening soil plasticity and geometrical non-linearity (P−Δ effects). After preliminary calibration of soil parameters, the FE model is successfully validated against literature results, namely obtained through (i) small-scale centrifuge experiments and (ii) numerical simulations based on macroelement foundation modelling. The validated FE model is then used to inspect several implications of soil modelling assumptions, as well as the response of the jack-up to relevant 3D loading combinations. The results presented support 3D continuum modelling as a suitable approach to analyse spudcan fixity and, overall, the operational performance of jack-ups. Despite higher conceptual/computational difficulties, fully 3D simulations can valuably complement the insight from (rare) integrated physical modelling, and contribute to the improvement of soil-spudcan macroelement models.