Effects of installation on combined bearing capacity of a spudcan foundation in spatially variable clay

Mobile jack-up drilling rigs with spudcan foundations are extensively used in offshore industry due to their flexibility, mobility and cost-effectiveness. A sufficient bearing capacity of the spudcan foundation is needed to resist the combined environmental loading associated with storms, winds, waves and currents. In most previous studies, the combined bearing capacity was defined for the wished-in-place spudcan foundation, ignoring the disturbance to the seabed soils cause by spudcan installation. It is shown in this paper how the installation affects the failure mechanism and bearing capacity of spudcan foundation in spatially variable soil. Random large deformation finite element method is first used to simulate the installation process of a spudcan foundation in order to obtain the disturbed soil strength profiles. Then the profiles are mapped into random small-strain finite element model for calculation of bearing capacity of the spudcan foundation. Results show that a large amount of the softer soils in the surface of seabed flow back to top of spudcan foundation, which causes the bearing capacity to reduce significantly. Moreover, a Monte-Carlo simulation is carried out to define the probabilistic failure envelopes of the spudcan foundation, considering the disturbance of installation to the spatially variable soils.