Numerical investigation on pullout capacity of helical piles under combined loading in spatially random clay

Helical piles are one promising foundation option in offshore industries to support wind turbines and floating structures. During service, the helical piles are subjected to combined loading originating from the superstructure and environmental factors. For the inclined pullout capacity of helical piles, several studies focused on the influence of helical plate configurations and soil properties. In contrast, this paper aims to assess the effect of the random distribution of soil strength. This is undertaken through the use of a large deformation random finite element analysis combing the random field theory, coupled Eulerian-Lagrangian method and Monte Carlo approach. Spatial variability and linearly increasing with depth of soil strength are modeled as a three-dimensional random field and a mean trend term. The probabilistic failure envelope as well as the failure mechanism can be then determined from each random realization. It is found that soil randomness has an insignificant influence on the failure mechanism. For different spatial soil configurations, the probabilistic failure envelopes vary widely from one another. An equation is established to fit the envelopes with different occurrence probabilities and probabilistic analyses are conducted. The present findings might help to improve the helical pile design practices to achieve better reliability.