Finite element modeling of suction caisson and large diameter monopile in dense sand under oblique and lateral load

Ahmed, Sheikh Sharif (2015) Finite element modeling of suction caisson and large diameter monopile in dense sand under oblique and lateral load. Masters thesis, Memorial University of Newfoundland.

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Abstract

Pile foundations have various kinds of applications in both onshore and offshore environments. The use of large-diameter piles with smaller length-to-diameter ratio installed in both sand and clay in offshore environments has increased significantly in last few decades. This thesis concentrates on the numerical modeling of large diameter suction caisson and monopile foundation systems installed in dense sand subjected to oblique pullout and eccentric lateral loading, respectively. In the first part of this thesis, three-dimensional finite element (FE) analyses have been performed to evaluate the inclined loading pullout capacity of suction caisson in dense sand. The numerical issues due to mesh distortion at large displacement have been reduced by the use of Arbitrary Lagrangian Eulerian (ALE) method offered by the commercially available Abaqus/Explicit FE software. The first set of the analyses has been conducted using the built-in Mohr-Coulomb (MC) soil model in Abaqus; however, it is unable to address the post-peak softening behavior of dense sand. In the next set, a modified form of Mohr-Coulomb (MMC) model has been employed by the aid of user-subroutine to capture the pre-peak hardening and post-peak softening behavior of dense sand. FE analyses results are compared with the centrifuge test results available in literature. The MMC model has been found to simulate better the soil behavior around the caisson. In the second part of the thesis, FE analyses have been performed to estimate the lateral load-carrying capacity of large diameter monopile in dense sand for different load eccentricities. The above mentioned MMC model has been employed in the simulations. The simulation results are compared with available centrifuge test results and a good match has been found. A parametric study has also been performed and a simplified method to estimate the capacity of monopile has been proposed. Analyses have also been conducted with the MC model. The comparison between the results obtained with the MMC and the MC models have been presented. The response of soil surrounding the monopile during loading is also examined.

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