Speaker
Description
Liquefaction of sands is a strongly multi-scale phenomenon governed by complex interactions between grain rearrangement, pore fluid flow, and phase transitions between solid-like and fluid-like states. Capturing these processes in a unified and thermodynamically consistent framework remains a major challenge for predictive modeling. In this contribution, we present two complementary phase-field models designed for the multi-scale simulation of liquefiable sands, addressing both the continuum and grain scales.
At the continuum scale, we introduce a phase-field formulation that distinguishes between sediment and suspension states. The sediment phase is modeled as a porous solid skeleton saturated with fluid, whereas the suspension phase exhibits fluid-mechanical behavior with negligible effective stress. The phase-field provides a smooth transition between these regimes, allowing the governing equations to remain well posed even in regions where the material locally loses shear strength and transitions from solid-like to fluid-like behavior. Within this framework, the balance laws of mass and momentum are formulated consistently across the sediment–suspension interface. The model is expressed in an Eulerian reference frame and implemented using the open-source finite element framework FEniCSx, enabling efficient and flexible numerical experimentation. Validation is carried out against laboratory experiments conducted at the German Federal Waterways Engineering and Research Institute (BAW), demonstrating that the model can reproduce key features of liquefaction and sediment mobilization observed in controlled hydraulic loading scenarios.
At the grain scale, we propose a second phase-field model that explicitly resolves the interaction between deformable solid grains and pore fluids under multiphase conditions. Here, the phase-field is used to distinguish between solid, liquid, and gas phases within a frictional granular assembly. This formulation allows the simulation of drainage and imbibition processes in partially saturated sands, including the evolution of complex fluid–fluid and fluid–solid interfaces. Surface tension effects are naturally incorporated and can induce grain displacements, leading to reconfiguration of the intergranular pore space. As a result, the model captures hydraulic–mechanical coupling during multiphase flow, including feedback mechanisms between capillarity, grain motion, and permeability evolution.
Together, the two models provide a coherent multi-scale perspective on wet granular media. The grain-scale simulations enable an enriched assessment of retention behavior and Bishop’s effective stress functions, accounting for micro-mechanically induced changes in saturation and stress transmission. These insights can be systematically upscaled and incorporated into the continuum-scale phase-field model, thereby improving its predictive capability for large-scale soil mechanics problems involving complex phenomena such as wetting collapse. The proposed framework opens new avenues for physically grounded modeling of liquefaction processes across scales, with potential applications in geotechnical, hydraulic, and coastal engineering.
| Country | Germany |
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