Current design practice of spudcans in clay generally ignores the influence of installation and subsequent operation on the spudcan elastic stiffness. In reality, soil consolidation around the post-installation spudcan can cause the elastic stiffness to evolve with time, thus affecting the safe and stable operation of jack-up platforms. This paper reports a numerical study dedicated to this specific subject. The spudcan installation and the time evolution of elastic stiffness coefficients during operation are continuously simulated using an effective stress large deformation finite element technique. The effects of soil, loading, embedment and geometric conditions were evaluated and interpreted. It was found that the non-uniform growth of the shear modulus caused by soil consolidation during operation results in the time evolution of the elastic stiffness and makes the deformation mechanism asymmetric. The overlap degree between the involved zone of the deformation mechanism and the growth zone of the shear modulus (or the so-called averaging effect) affects the gradient of time evolution. Based on the parametric study, a generalized framework is present for predicting the elastic stiffness coefficients of spudcans for different scenarios and consolidation times, thus providing a complete view of the time evolution of elastic stiffness for the offshore in-site assessment.@en

The bending moment response of straight pile foundations, as the dominant factor of spudcan-pile interaction, has received focused attention in the close joint operation between jacket platforms and jack-up drilling rigs. As the foundation for the same widely used in jacket platforms, the research on the batter pile is still a knowledge gap in this field. This paper presents a numerical study of the bending moment response of batter piles at different inclination angles and azimuthal angles during spudcan installation. Using a coupled Eulerian-Lagrangian finite element method, the effects of flexural rigidity, stiffness ratio, spudcan-pile clearance distance, and pile length on the pile head bending moment were sequentially evaluated. It was found that the pile bending moment response is related to the change in soil flow mechanism caused by spudcan penetration and becomes more significant with the increase of inclination angle; under the same inclination angle, the bending moment response is the most dangerous when the azimuthal angle is 0°. Based on the parameter study, a simple method is proposed to estimate the pile head bending moment during spudcan installation. The outcome may facilitate incorporating pile spatial inclination into spudcan-pile interaction research and contribute to related safety design.@en

Determining the elastic stiffness coefficient of spudcan foundations is a challenging task due to the natural variability of soil properties coupled with the complexity of loading conditions. Uncertainty in the elastic stiffness coefficient is a potential risk factor for the safe and stable operation of offshore jack-up platforms, and there are no guidelines for operators to assess its confidence level. This paper conducted a study on this specific subject using the three-dimensional random finite element method. The influence of soil strength heterogeneity, the coefficient of variation and the scale of fluctuation of the shear modulus, embedment depth and soil backflow on the deformation mechanism and elastic stiffness coefficient of spudcans were systemically discussed. The results suggest that the above parameters, combined with the soil's spatial variability, can alter the deformation mechanism, thereby the elastic stiffness coefficient. If spatial variability is ignored in platform design, the safety probability of spudcans is only 50%. So, a matrix algebraic expression is proposed to accurately predict the elastic stiffness coefficient in spatially variable clay at any given confidence level. The study findings may facilitate incorporating spatial variability into elastic stiffness research and supplement the calculation method in the existing jack-up assessment guidelines.@en