Modelling the effects of pauses during spudcan penetration on the further installation behaviour

The installation of jack-up platforms may result in a discontinuous process due to either expected or unexpected delays experienced while penetrating. For this reason, it is important to correctly estimate not only the response of the soil during penetration but also the effect that a period of consolidation of variable length can have on further penetration. Modelling this problem numerically would allow a wider parametric study to be conducted in an economic fashion. However, it requires a large deformation approach, where coupled pore fluid pressure effective stress analyses are able to describe the buildup of excess pore pressure during penetration as well as the relative dissipation during a stage of consolidation, with relative increases in the strength of the soil in the vicinity of the spudcan. For this reason, an advanced hypoplastic numerical model within the framework of the critical state soil mechanics for structured clays was implemented. Additionally, by implementing the structure within the model, the soil degradation due to shear strains can be described, starting the analysis with an intact shear strength that is gradually degraded as the spudcan advances. The response after consolidation is compared with results from experimental tests in a centrifuge environment at enhanced gravity, where a spudcan model equipped with a pore pressure transducer was penetrated. The results show that the effects of a period of consolidation must be taken into account because, depending on its length, it could lead to a significant increase in the bearing capacity on re penetration due to the stiffening and strengthening of the soil, thereby offering insight into a potential shallower and yet reliable installation depth.