Numerical simulations of static liquefaction in submerged slopes

Abstract

The static liquefaction tank (SL-tank) is a unique large-scale facility that provides a means to simulate the conditions of a submerged soil slope under failure conditions. Static liquefaction (SL) may be defined as a significant loss of soil’s shear strength due to a substantial development of excess pore water pressure under monotonic loads. This complex soil behavior is commonly related to case studies such as submarine flow slides.
The main objective of this project is to use a finite element method (FEM) based on a Hypoplasticity (HP) framework to numerically simulate the experimental data obtained from the Static liquefaction tank facility of Delft University of Technology. A set of Elasto-Plastic (EP) constitutive models were chosen as an initial reference to simulate the SL-tank and afterwards compare their results to the HP framework. The numerical results were analyzed mainly in terms of excess pore water pressure and relating them to experimental data. Additionally, effective stresses, strains and stress paths were examined from the given model outputs.
A fine-cohesion less soil called Geba sand was used in the experimental procedure of the SL-tank, as well as in elements tests performed within this study. The model parameter determination and calibrations were performed by means of element tests, empirical correlations, theoretical formulations, and best-fits from experimental data. Soil behavior at low stresses is of fundamental importance for the performed experiments and numerical simulations in this work.
A potential instability behavior from the given numerical simulations was studied by means of an adopted instability line (IL). The IL criteria is a framework which is commonly illustrated in stress paths as a boundary that delimits a potential susceptibility to soil collapse. Element test data from fine-loose sands, as well as the numerical outputs from this work were used for estimating a potential IL applicable for the scope of this Master’s thesis project.
Results of this investigation showed clear limitations of the hypoplasticity constitutive laws in generating sufficient excess pore water pressures and deformations to trigger static liquefaction. Additionally, boundary effects in the assumed fixity conditions were a main potential issue regarding inaccurate results. Nevertheless, an enhanced model response (HP) was observed in comparison to Elasto-Plastic models.