Predicting large diameter pile running in spatially variable soils

Abstract

Large-diameter driven piles are widely used as foundations for offshore wind turbines and platforms. During installation, unexpected pile running can result in rapid, uncontrolled penetration of the pile into the seabed due to the large self-weight. This paper assesses the risks of pile-running for large diameter driven piles in spatially variable soils using a procedure based on the American Petroleum Institute bearing capacity guidelines combined with Newton’s Second Law of Motion. This differs from conventional static bearing capacity analyses by calculating the pile velocity with depth. One-dimensional random fields are implemented to simulate downward spatially variable shear strengths. While fluctuations in shear strengths do not provide sizable impacts to pile shaft resistance at larger depths, end-bearing resistance variability can provide appreciable changes to pile running velocities and penetration depths. Results of the spatially variable formulation are compared with Large Deformation Finite Element simulation, providing strong agreement. Of particular importance is the conclusion that pile running analyses where soil variability is ignored can lead to unconservative estimates of velocity and depth profiles. The simplified probabilistic method for assessing heterogeneous soil properties is especially important, given that unexpected weak layers are one of the primary factors contributing to pile running.