Numerical Investigation of the Installation of Suction Caisson in Sand Using Material Point Method

Abstract

Suction caisson has gained interest in recent years as an alternative foundation for offshore wind turbines due to its cost-effectiveness and easy installation compared to conventional foundations such as monopile. After initial penetration due to its self-weight, suction is applied until the caisson reaches the desired depth. Applying suction provides additional driving force due to the pressure difference between inside and outside the caisson and induces seepage that degrades friction and tip resistance, which further facilitates the installation. The seepage plays a vital role in installing suction caisson in sand; however, it might change the soil state which affects the ultimate bearing capacity of the caisson. Several research works have been conducted to study the suction caisson installation in sand. However, the complexities of the problem including large deformation, solid-fluid and soil-structure interaction, inhibited these studies from fully understanding the installation mechanism. This paper proposes a large deformation modeling framework by using the material point method (MPM). MPM is a hybrid Lagrangian-Eulerian particle-based method that uses material points over a fixed computational mesh where governing equations are solved. During the convection of the particles, the background mesh is kept fixed, making it suitable for large deformation problems. The model considers soil-structure interaction by adopting a Coulomb contact algorithm between the caisson and surrounding soil. In this paper, the stability of the contact algorithm is ensured by correcting material point velocities in the vicinity of the caisson interface using a limiting velocity based on the element size and time step. The framework is validated by comparing a simulation of caisson installation under constant velocity with results published in the literature. Our proposed framework’s results agree with previous published results, demonstrating that the simplified stabilization procedure does not affect the simulation results. This is a promising result that will enable the incorporation of fully coupled analysis to better understand the effects of induced seepage on the installation mechanism of suction caissons.