Undrained Bearing Capacity of Suction Caissons for Offshore Wind Turbine Foundations by Numerical Limit Analysis

Determining the ultimate capacity of suction caissons in response to combined vertical, horizontal, and moment loading is essential for their design as foundations for offshore wind turbines. However, the method implemented for stability analysis is quite limited. Numerical limit analysis has an advantage over traditional limit equilibrium methods and nonlinear finite element methods in this case because upper and lower bounds can be achieved to ensure that the exact ultimate capacity of the caisson falls within the appropriate range. This article presents theories related to numerical limit analysis. Simulations are conducted for centrifuge model tests, the findings of which reveal the ability of numerical limit analysis to deal with the inclined pullout capacity of suction caissons. Finally, this article proposes an estimation of the ultimate capacity of a 3.5 MW offshore wind turbine foundation on normally consolidated clay based on the typical environmental parameters of Bothkennar, Scotland. Undrained failure envelopes and safety factors are obtained for suction caissons with different embedment ratios. Failure mechanisms, plastic zones, clay stress distributions, and the influence of the skin friction coefficients of caissons are discussed in detail.