A hydrodynamic theory for clay

• Applicant: Dr.-Ing. Max Wiebicke
• Subject Area: Geotechnics, Hydraulic Engineering ; Applied Mechanics, Statics and Dynamics
• Term: from 2021 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 457695076

Clays are soils that show a very complex macroscopic behaviour. As such, they experience pronounced rate effects as well as a strong dependency on their thermo-hydro-chemo-mechanical environment. In geotechnical engineering, this behaviour is generally predicted using constitutive models, which are mostly phenomenological. Historically, these models were set up to describe experimental observations, that were only measurable on the boundary of the specimen in so called element tests. These phenomenological models use inner variables and parameters, whose physical meaning is often unclear.It is known that the origin of the macroscopic behaviour and the peculiarities of particulate materials such as clays originate from processes at lower scales. Due to the small size of clay particles, their interaction is governed by mechanical as well as electro-chemical forces. These lead to a distinct behaviour at the particle-scale, for example the collective behaviour of clay particles within aggregates. Incorporating such physical interactions at the lower scales, that dictate the macroscopic behaviour, into the constitutive models leads to a more rational, physics-based modelling with state variables that have a clear physical meaning and can consequently lead to models that capture the phenomena naturally.The goal of this project is to build a new physics-based, advanced mathematical constitutive theory for clay using a hydrodynamic-plastic framework. This model will be designed to clearly reflect the complex interplays between intrinsic yet clearly identifiable scales of kinematics within the material. Contrary to granular materials, such as sands, where the scale of particle kinematics is important, there is at least one more scale to consider in clay, as their elementary particles form aggregates whose kinematics include an ongoing build up, collapse, and collective motions that distinctly influence their macroscopic behaviour. There is an overwhelming amount of constitutive phenomena arising due to the interplays between these identifiable scales that are currently only considered in a purely phenomenological way through available constitutive models. Examples include the whole family of critical state models which cannot systematically explain all the rich rate-dependent phenomena, including creep, ageing, transients, and gradual progression into critical state and collapse under unfavorable stress configurations. The purpose of this project will be to resolve this gap by developing a comprehensively predictive constitutive model for clay that is based on a novel hydrodynamic-plastic theory, which is rooted on physics through hydrodynamics and mathematics through plasticity modelling tools.

• DFG Programme: WBP Fellowship
• International Connection: Australia
• Host: Professor Dr. Itai Einav