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

摘要

Pile foundations have various kinds of applications in both onshore and offshoreudenvironments. The use of large-diameter piles with smaller length-to-diameter ratioudinstalled in both sand and clay in offshore environments has increased significantly in lastudfew decades. This thesis concentrates on the numerical modeling of large diameter suctionudcaisson and monopile foundation systems installed in dense sand subjected to obliqueudpullout and eccentric lateral loading, respectively.udIn the first part of this thesis, three-dimensional finite element (FE) analyses have beenudperformed to evaluate the inclined loading pullout capacity of suction caisson in denseudsand. The numerical issues due to mesh distortion at large displacement have been reducedudby the use of Arbitrary Lagrangian Eulerian (ALE) method offered by the commerciallyudavailable Abaqus/Explicit FE software. The first set of the analyses has been conductedudusing the built-in Mohr-Coulomb (MC) soil model in Abaqus; however, it is unable toudaddress the post-peak softening behavior of dense sand. In the next set, a modified form ofudMohr-Coulomb (MMC) model has been employed by the aid of user-subroutine to captureudthe pre-peak hardening and post-peak softening behavior of dense sand. FE analyses resultsudare compared with the centrifuge test results available in literature. The MMC model hasudbeen found to simulate better the soil behavior around the caisson.udIn 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 loadudeccentricities. The above mentioned MMC model has been employed in the simulations.udThe simulation results are compared with available centrifuge test results and a good matchudhas been found. A parametric study has also been performed and a simplified method toudestimate the capacity of monopile has been proposed. Analyses have also been conductedudwith the MC model. The comparison between the results obtained with the MMC and theudMC models have been presented. The response of soil surrounding the monopile duringudloading is also examined.