PROGRAMME OF THE ALERT OLEK ZIENKIEWICZ SCHOOL ON CONSTITUTIVE MODELLING OF GEOMATERIALS 2025

DATES: February 3 to February 7, 2025

VENUE: Charles University, Prague, Czech Republic

ADDRESS: Albertov 6, Prague 2 (https://maps.app.goo.gl/wsBswVDJW75DbVWX7)

REGISTRATION FEE: Free, but space is limited to 60 participants and, should the place be fully booked, ALERT institution PhD students will be provided access with a priority. Priority held till November 30, 2024.

REGISTRATION LINK: https://soilmodels.com/alert-oz-school-2025-registration

TRAVELLING, ACCOMMODATION AND OTHER ARRANGEMENTS: By registering, the participants confirm they will attend the event in person for the full duration. There is no support provided by the organisers for travel and accommodation. Lunch sandwiches and refreshments during coffee breaks will be provided.


LIST OF SPEAKERS (INCLUDING LECTURE + HANDS-ON SESSION UNITS OF 50 MIN. EACH):

prof. David Mašín, Charles University, Prague, Czech Republic: 6+0

prof. Claudio Tamagnini, University of Perugia, Italy: 6+0

prof. Ivo Herle, Technical University of Dresden, Germany: 4+0

Dr. Gertraud Medicus, University of Innsbruck, Austria: 1+4

Dr. Alexandros Petalas, Durham University, UK: 3+1

Dr. Merita Tafili, Ruhr University Bochum, Germany: 4+0

Dr. Filippo Masi, University of Sydney, Australia: 2+1

TOTAL LECTURE + HANDS-ON SESSION UNITS: 26+6


MONDAY [FUNDAMENTALS]

8:20-8:30 > Introduction, organisation [MASIN ET AL]

8:30-9:20 > Fundamentals of soil testing [HERLE]

-> Fundamentals of soil testing – typical test setups, loading parts and test outputs. Limitations with respect to the assumptions (element test). Analysis of the behaviour inside the soil specimens.(localization of strains, inhomogeneous response).

9:30-10:20 > Basic features of soil behaviour [HERLE]

-> Basic soil mechanics features of soil behaviour like stiffness (stress-dependence), limit stresses (strength), critical states and asymptotic behaviour. Drained versus undrained behaviour.

10:30-11:20 > Basic features of soil behaviour – explained graphically [MEDICUS]

-> Basic features of soil behaviour are explained using interactive images. Principal stress space, normal compression lines, state boundary surfaces, strength envelopes, etc. are explained graphically. Also, response envelopes are introduced here. This lecture will not be focused on specific models yet, but  references to particular models will be given – the students will have a feeling about them before they will be introduced mathematically later.

11:30-12:20 > hands-on: Basic features of soil behaviour [MEDICUS]

-> Students will be asked and guided to investigate interactive graphics made available at SoilModels by Gertraud Medicus. The exercise will be  a smooth continuation of the previous lecture.

LUNCH

13:30-14:20 > Elasticity and hyperelasticity [TAMAGNINI]

14:30-15:20 > Perfect plasticity [TAMAGNINI]

-> Two introductory lectures on perfect plasticity modelling, including the elastic component of the models. In the first part,the concepts of hypoelasticity and hyperelasticity are introduced and their differences highlighted in view of the subsequent lectures on cyclic loading models, where minor artificial strain accumulation in the elastic regime may play an important role.

15:30-16:20 >  Hardening plasticity – basic concepts, critical states [TAMAGNINI]

-> Introduction to the basic principles of classical isotropic and anisotropic hardening plasticity. Application of isotropic hardening plasticity to Critical State soil mechanics: the modified Cam-clay model,

16:30-17:00 > Questions & Answers, discussion session [ALL]

TUESDAY [BASIC CONCEPTS]

8:30-9:20 > Hardening plasticity – bounding surface models [PETALAS]

-> Introduction to single-surface Kinematic Hardening plasticity. Possibilities and limitations. Fundamentals of Bounding Surface (two-surface) plasticity theory for cyclic loading and ratcheting of metals. Advanced two-surface plasticity models for soils as an extension of the Cam-clay model (e.g. Mroz et al 1979).

9:30-10:20 > Hardening plasticity – kinematic shear hardening [PETALAS]

-> Application of two-surface plasticity for state-dependent sand modelling; the SANISAND family of models. Incorporation of Critical State Soil Mechanics. Possibilities and limitations. Introduction to Anisotropic Critical State Theory. Fabric-based soil constitutive modelling; the SANISAND-F model.

10:30-11:20 > Hypoplasticity without critical states [HERLE]

-> Basic introduction to hypoplasticity. Incremental nonlinearity, loading and unloading within one equation, definition of the limit stress state. Calibration procedure.

11:30-12:20 > hands-on: Cam-clay calibration [MEDICUS]

-> Our first exercise, where students will be provided with experimental data to be used throughout the week. Studentswill manually do the calibration of the Modified Cam Clay Model and carry out their model’s predictions using an Incremental Driver.

LUNCH

13:30-14:20 > Hypoplasticity with critical states [MASIN]

-> Incorporation of critical states into hypoplasticity (research by Karlsruhe group resulting in a model by von Wolffersdorff, 1996), independent limit surface formulation of Niemunis (2009), basic clay hypoplasticity by Masin (2005).

14:30-15:20 > Hypoplasticity with asymptotic states [MASIN]

-> Calculation of swept-out-memory surface of earlier critical state hypoplastic models, explicit incorporation of asymptotic states into hypoplasticity, model by Masin (2013).

15:30-16:20 > hands-on: Clay hypoplasticity calibration [MEDICUS]

-> Calibration of Masin (2013) clay model. This is for the students to specifically see the effect of non-linear formulation when opposed to Cam-clay calibrated earlier. Asymptotic states will be comparable, the behaviour before reaching asymptotic states different for overconsolidated samples, similar in normally consolidated samples. This exercise will be carried out similar to the previous exercise on Modified Cam clay model calibration.

16:30-17:00 > Questions & Answers, discussion session [ALL]

WEDNESDAY [SMALL STRAIN NON-LINEARITY AND CYCLIC LOADING]

8:30-9:20 >  Behaviour of soils at small strains [HERLE]

-> Experimental methods for the determination of the stiffness at small strains. Stiffness degradation with straining (quasi-)elastic stiffness in the very small strain range. Role of the recent strain/stress history and swept-out memory.

9:30-10:20 > Small strain stiffness predictions in constitutive models [MASIN]

-> Early non-linear elastic models for small strain stiffness predictions, description of the intergranular strain concept (Niemunis and Herle, 1997) for hypoplasticity, predictions of the recent stress history effects by kinematic hardening critical state models (3-SKH model by Stallebrass and Taylor, 1997).

10:30-11:20 > Behaviour of soils under cyclic loading [TAFILI]

-> Description of concepts of soil cyclic response. Cyclic accumulation of strain in drained and undrained conditions, cyclic accumulation of pore water pressures in undrained conditions, liquefaction and its dependency on soil type, concept of CNR-N curves, the effect of monotonic and cyclic preloading, applicability of Miner’s rule, high cyclic effects.

11:30-12:20 > hands-on: SANISAND calibration [PETALAS]

-> This hands-on session will follow the clay hypoplastic model calibration. Students will here be provided with a new spreadsheet with sand data and will be guided through manual calibration of the SANISAND model using Incremental Driver.

LUNCH

13:30-14:20 > Cyclic loading predictions in elasto-plasticity [PETALAS]

-> Kinematic hardening model prediction for cyclic loading of sands (e.g., SANISAND, Severn-Trent sand). New developments for kinematic hardening models focusing on sand ratcheting; the memory surface extension. Dafalias/Popov bounding-surface plasticity framework for sand ratcheting.  

14:30-15:20 > Cyclic loading predictions in hypoplasticity [TAFILI]

-> This lecture will showcase the capabilities of intergranular strain coupled with hypoplasticity in predicting the behavior of soils under cyclic loading. We will explore the extended models, including ISA-combined with hypoplasticity, the concept limiting strain accumulation, ISI, and the new pre- and post-liquefaction hypoplastic model with fabric change effects and semifluidized state. While briefly touching on the underlying formulations, the emphasis will be placed on the predictive strengths and practical applications of these advanced models in geotechnical engineering.

15:30-16:20 > High-cycle accumulation models [TAFILI]

-> This lecture delves into the HCA model (High-Cycle Accumulation) developed by Niemunis and Wichtmann (2005), focusing on its alternating explicit and implicit calculation stages. The detailed explanation will highlight the model’s concepts and the challenges in efficiently controlling stresses. We will also discuss the use of cyclic accumulation charts, which visualize the progressive changes in soil behavior under repeated loading. Additionally, the lecture will cover the newly developed accelerated implicit method, designed to improve computational efficiency for implicit models.

16:30-17:00 > Questions & Answers, discussion session [ALL]

THURSDAY [MULTIPHYSICS AND ADVANCED TOPICS]

8:30-9:20 > Partial saturation, HM coupling [MASIN]

-> The effect of partial saturation on soil behaviour, concept of effective stress under unsaturated conditions, coupling mechanical models with water retention models.

9:30-10:20 > Grain crushing, cementation, temperature, double structure [MASIN]

-> Grain crushing and cementation, temperature effects on soil behaviour, double structure modelling framework for predicting highly swelling clays.

10:30-11:20 > Time and rate effects [TAFILI]

-> In this lecture, we will investigate the time- and rate-dependency of fine-grained soils and its introduction into constitutive models. Various concepts like elasto-viscoplasticity and viscohypoplasticity, focusing on their applications in predicting creep and relaxation behaviours of materials subjected to slower loading rates will be analysed. Key mechanisms and formulation approaches will be discussed to understand how these models effectively capture time-dependent deformations. Additionally, the lecture will transition to the modelling of high loading rates, incorporating the inertial number and the μ(I) rheology concept.

11:30-12:20 > Hyperplasticity  [TAMAGNINI]

-> Introduction of the theory of hyperplasticity, based on the principles of thermomechanics of continuous media and convex analysis.

LUNCH

13:30-14:20 > Introduction to Machine Learning  [MASI]

-> We explore some fundamentals of Machine Learning (ML) and regression concepts with a focus on neural networks. We begin by introducing linear regression and its optimization via gradient descent. The focus then shifts to neural networks for regression, where we demonstrate their power in capturing nonlinear relationships.

14:30-15:20 > Constitutive modelling meets Machine Learning: theory and applications [MASI]

-> We explore how to integrate principles stemming from physics and thermodynamics in ML algorithms for the identification of constitutive models from data, in an equation-free manner. Practical examples are used to illustrate how physical knowledge can be incorporated as learning and inductive biases to build accurate, data-driven models.

15:30-16:20 > hands-on: Machine learning models  [MASI]

-> Implementation and use of a few benchmarks of data-driven methods in physics and constitutive modelling.

16:30-17:00 > Questions & Answers, discussion session [ALL]

FRIDAY [IMPLEMENTATION AND BVP]

8:30-9:20 > Implementation, time-integration [TAMAGNINI]

-> Stress-point algorithms for the implementation of constitutive models in finite element codes. Explicit time-integration schemes (Forward Euler, Runge-Kutta methods) with adaptive substepping. Drift correction methods. Implicit time-integration schemes: the Generalised Backward Euler algorithm for hardening plasticity models.

9:30-10:20 > Finite deformation plasticity [TAMAGNINI]

-> Introduction to additive and multiplicative finite deformation plasticity theories, Finite deformation multiplicative hyperplasticity. Examples of application in PFEM simulations of CPTu testing..

10:30-11:40 > Advanced constitutive models in BVP predictions [MASIN]

-> Selection of a few case studies demonstrating that choice of advanced models has an important effect on predictions.

11:50-13:00 > hands-on: Automatic calibration of the models using EXCALIBRE [MEDICUS]

-> Final hands-on session adopting automatic model calibration using ExCalibre online tool. Students will finally deal with different models, possibly including recalibration of their manual efforts from previous sessions. Students will compare parameter values which they already calibrated manually with automatically calibrated values (for Cam clay and clay hypoplasticity). Also, they will compare predictions of models which they did not calibrate manually (sand hypoplasticity of von Wolffersdorff) with predictions of SANISAND which they produced on their own.

13:00 > Closure [MASIN ET AL]

LUNCH

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