Optimisation of the thermo-hydro-mechanical modelling of geomaterials

• Research unit: COST
• Project number: C02.0009

Key words (English)

Numerical optimisation; numerical modelling; natural materials (geomaterials); underground structures

Research programs (English)

COST-Action 526 - Automatic Process Optimization in Materials Technology

Short description (English)

See abstract

Partners and International Organizations (English)

B, CZ, DK, FIN, F, D, H, PL, SI, CH, GB

Abstract (English)

Large civil engineering projects very often encounter situations where complex behaviour of (polyphasic) materials has to be modelled numerically, while most available numerical tools are designed to handle artificial materials with perfectly controlled parameters. Model calibration based on laboratory tests faces many difficulties: time and scale effect, sample disturbances or model complexity. Under such circumstances the numerical modelling of geomaterials still is based on computational approximation and empirical knowledge, which may induce some inaccuracy. This project contribute to the improvement of the numerical modelling of the Thermo-Hydro-Mechanical (THM) behaviour of geomaterials by: i. Extension of the capability of our numerical tool (Finite Element Code); ii.Validation of the Thermo-Hydro-Mechanical (THM) numerical approach; iii. Introduction of numerical optimisation processes to numerical modelling of THM processes. The research work was mainly concentrated on the following subjects: · Mathematical formulation of the THM processes, development of the Finite Element Code and its verification. · Optimisation algorithms: development and application to themo-hydro-mechanical constitutive law (LTVP model). The fully coupled three-phase formulation has been developed based on the continuum theory of mixtures using as principal variables: the temperature, the solid displacement, the liquid pressure and the gas pressure. The formulation of the heat balance equation takes into account thermal coupling with solid and fluid phases. The resulting system of equations is discretized in space using the finite element technique and in time by the Q - method. A simplified version of the full equations is proposed. The developed THM mathematical model has been implemented into the Finite Element Code - MHERLIN, which is operational at the moment. The main tasks in the domain of optimisation was finding of appropriated optimisation strategy and its applicatin to the numerical modelling of the thermo-hydro-mechanical behaviour of clay barriers. The proposed methodology is a combination of quasi-Newton and stochastic methods applicable at local and global levels, respectively. The code ParaID combines these two methods and applies to the thermo-elasto-plastic (LTVP) constitutive model. The procedure and the developed code have been validated for drained as well as undrained triaxial shear tests for three different initial stess states. Comparison between numerical and experimental results clearly shows the capability of the optimisation procedure to derive model parameters correctly. References Cekerevac, C., and Laloui, L. 2004. Experimental study of thermal effects on the mechanical behaviour of a clay. International Journal for Numerical and Analytical Methods in Geomechanics incorporating Mechanics of Cohesive-frictional Materials, 28(3): 209-228. Laloui, L., and Cekerevac, C. 2003. Thermo-plasticity of clays: An isotropic yield mechanism. Computers and Geotechnics, 30(8): 649-660.

References in databases (English)

Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. [phone] Swiss Project-Number: C02.0009