A methodology to calibrate the PICSI cyclic p-y model using experimental results and optimisation

Abstract

Fatigue life estimation of the components of a drilling conductor system is often a critical design consideration. The analysis is usually performed using a coupled system, with the soil-conductor interaction modelled using p-y springs that remain constant throughout the analysis. This means that shifts in bending moment profile that occur due to degradation and recovery of the soil during or after cycling are not accurately modelled. While the PICSI framework (White et al., 2022) can model changes in stiffness and strength of p-y curves due to cycling and pore-pressure dissipation, guidance has not yet been provided on how to calibrate its parameters. This paper presents an experimental methodology for this calibration process based on centrifuge and p-y model testing in reconstituted carbonate silt and kaolin clay. The procedure uses numerical optimisation, and the calibrated parameters are validated against results from an independent set of centrifuge tests on carbonate silt using a flexible pile of similar dimensions to a conductor. It is found that the calibrated model is able to match the changes in cyclic bending moment through a sequence of different packets of cyclic loading. This calibration procedure provides an objective approach for more accurate modelling of conductor fatigue.