Abstract

Many geotechnical problems involve large deformations, non-linear material behaviour, soil-structure interactions, and multiphase (solid, liquid, gas) interactions, which poses significant challenges for numerical simulations. The material point method (MPM) showed to be well suited to study slope instabilities, such as landslides, earth embankment and levee failures, underground excavations, explosions, soil-penetration problems, such as pile installation, Cone Penetration Testing, Free Fall Penetrometer testing, etc. Moreover, erosion and sedimentation problems require considering phase transitions (from solid-like to fluid-like), and This contribution will show the latest numerical developments of MPM with respect to the above-mentioned aspects as implemented in the open-source software Anura3D. Particular attention is given to some geotechnical applications, such as the simulation of slope collapse due to earthquake or water pressure changes, erosion problems, porous sea defences, installation problems, and many more.

Abstract

Cone penetration tests (CPTs) can provide quantitative information about the mechanical state of sandy soils. In the current state of the art, the soil state is derived from the cone resistance, which is estimated from the cavity expansion solution and a calibrated scaling equation. Recently, Martinelli and Pisano (2022) showed that MPM simulations of CPTs provide accurate values of the cone resistance in sandy soils when using the critical state NorSand model. This paper adopts this framework to develop a predictive equation for cone resistance as a function of the NorSand parameters and the state parameter of the soil. This formula is straightforward to implement, and it can be adopted by researchers and practitioners to assess soil state in a soil deposits.

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.