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Numerical modeling of coupled thermo-hydro-mechanical processes in geological porous media
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Coupled Thermo-Hydro-Mechanical (THM) behavior in geological porous media has been a subject of great interest in many geoengineering disciplines. Many attempts have been made to develop numerical prediction capabilities associated with topics such as the movement of pollutant plumes, gas injection, energy storage, geothermal energy extraction, and safety assessment of repositories for radioactive waste and spent nuclear fuel. This thesis presents a new numerical modeling approach and a new computer code for simulating coupled THM behavior in geological porous media in general, and compacted bentonite clays in particular, as buffer materials in underground radioactive waste repositories.

New governing equations were derived according to the theory of mixtures, considering interactions among solid-phase deformation, flows of water and gases, heat transport, and phase change of water. For three-dimensional problems, eight governing equations were formulated to describe the coupled THM processes.

A new thermal conductivity model was developed to predict the thermal conductivity of geological porous media as composite mixtures. The proposed model considers the combined effects of solid mineral composition, temperature, liquid saturation degree, porosity and pressure on the effective thermal conductivity of the porous media. The predicted results agree well with the experimental data for MX80 bentonite.

A new water retention curve model was developed to predict the suction-saturation behavior of the geological porous media, as a function of suction, effective saturated degree, temperature, porosity, pore-gas pressure, and the rate of saturation degree change with time. The model was verified against experimental data of the FEBEX bentonite, with good agreement between measured and calculated results.

A new finite element code (ROLG) was developed for modeling fully coupled thermo-hydro-mechanical processes in geological porous media. The new code was validated against several analytical solutions and experiments, and was applied to simulate the large scale in-situ Canister Retrieval Test (CRT) at Äspö Hard Rock Laboratory, SKB, Sweden, with good agreement between measured and predicted results. The results are useful for performance and safety assessments of radioactive waste repositories.

Place, publisher, year, edition, pages
Stockholm: KTH , 2010. , xiv, 84 p.
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1055
Keyword [en]
Thermo-hydro-mechanical processes; Porous geologicalmedia; Numerical modeling; FEM; Multiphase flow; Effective thermal conductivity; Water retention curve; Radioactive waste repositories;Bentonite;
National Category
Geophysical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-12009ISBN: 978-91-7415-554-9 (print)OAI: oai:DiVA.org:kth-12009DiVA: diva2:294022
Public defence
2010-03-12, F3, Lindstedtsvägen 26, KTH, Stockholm, 16:15 (English)
Opponent
Supervisors
Projects
THERESA
Note
QC20100720Available from: 2010-02-26 Created: 2010-02-15 Last updated: 2010-07-20Bibliographically approved
List of papers
1. A fully coupled thermo-hydro-mechanical model for simulating multiphase flow, deformation and heat transfer in buffer material and rock masses
Open this publication in new window or tab >>A fully coupled thermo-hydro-mechanical model for simulating multiphase flow, deformation and heat transfer in buffer material and rock masses
2010 (English)In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, Vol. 47, no 2, 205-217 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents a numerical method for modeling coupled thermo-hydro-mechanical processes of geomaterials with multiphase fluid flow. A FEM code has been developed and validated for modeling the behavior of porous geological media, and is equally applicable for modeling coupled THM processes in rocks. The governing equations are based on the theory of mixtures applied to the multiphysics of porous media, considering solid phase deformation, multiphase fluid flow, and heat transport. New numerical techniques have been developed for more efficient FEM formulation and equation solution for modeling saturated or partially saturated water flow, gas flow and heat transfer indeformable porous media, as are commonly encountered in performance and safety assessment of underground radioactive repositories. The code has been validated against an experimental benchmark test, which involves bentonite under laboratory conditions, with good results. Several critical outstanding issues for modeling coupled processes of geomaterials are discussed indepth.

Keyword
WATER-RETENTION CURVE; UNSATURATED POROUS-MEDIA; RELATIVE PERMEABILITY; SOILS; CONDUCTIVITY; BENTONITE; STATE; CONSOLIDATION; FORMULATION; HYSTERESIS
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-12027 (URN)10.1016/j.ijrmms.2009.11.002 (DOI)000274550200003 ()2-s2.0-76349100273 (Scopus ID)
Note
QC 20100720Available from: 2010-02-19 Created: 2010-02-19 Last updated: 2012-02-14Bibliographically approved
2. An effective thermal conductivity model of geological porous media for coupled thermo-hydro-mechanical systems with multiphase flow
Open this publication in new window or tab >>An effective thermal conductivity model of geological porous media for coupled thermo-hydro-mechanical systems with multiphase flow
2009 (English)In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, Vol. 46, no 8, 1358-1369 p.Article in journal (Refereed) Published
Abstract [en]

The objective of this paper is to present the development of an effective thermal conductivity model for simulation of thermo-hydro-mechanical processes of geological porous media. The Wiener bounds and Hashin-Shtrikman bounds for thermal conductivity of three-phase mixture are introduced first, followed by descriptions of thermal conductivities of gas, water and solid, respectively. The derivation of a new effective thermal conductivity model, in closed form, is then presented. The model considers the combined effects of solid mineral composition, temperature, liquid saturation degree, porosity and pressure on the effective thermal conductivity of porous media, when multiphase flow with phase change is involved. The model strictly obeys the Wiener bounds (for anisotropic media) and Hashin-Shtrikman bounds (for isotropic media) over wide ranges of porosities and saturations, and the predicted results agrees very well with the experimental data for MX80 bentonite, compared with Johansen's method. An experimental benchmark test problem under laboratory conditions for coupled thermo-hydro-mechanical processes of compacted FEBEX bentonite is simulated for validation of the model, and the results show that the model provides improved predictions of the evolution and distribution of temperature, with simpler forms of mathematical functions. (C) 2009 Elsevier Ltd. All rights reserved.

Keyword
Thermal conductivity, Thermo-hydro-mechanical (THM), Geological porous media, Wiener bounds, Hashin-Shtrikam bounds, Buffer material, Multiphase flow, SOIL, TEMPERATURE, WATER, AIR, NITROGEN, BUFFER, OXYGEN, RANGE, ARGON
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-12028 (URN)10.1016/j.ijrmms.2009.04.010 (DOI)000272940400011 ()2-s2.0-70449527769 (Scopus ID)
Note
QC20100720Available from: 2010-02-19 Created: 2010-02-19 Last updated: 2010-07-20Bibliographically approved
3. A Water Retention Curve Model for the Simulation of Coupled Thermo-Hydro-Mechanical Processes in Geological Porous Media
Open this publication in new window or tab >>A Water Retention Curve Model for the Simulation of Coupled Thermo-Hydro-Mechanical Processes in Geological Porous Media
2012 (English)In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 91, no 2, 509-530 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents a new water retention curve (WRC) model for the simulation of coupled thermo-hydro-mechanical processes in geological porous media. The model simultaneously considers the impact of porosity and temperature on suction, for both wetting processes and drying processes. The model is based on an idealization of porous geological media as having an isotropic and homogeneous microscopic pore structure. Suction is expressed as a function of degree of saturation, porosity, surface tension of the water-air interface, and the length of air bubble perimeter of the pores per unit area on a random 2D cross-section of the medium. The tension of water-air interface is written as a function of temperature, and the length of perimeter of the water-air interface of the pores becomes a function of porosity and degree of saturation. The final equation of the new WRC is a function of suction, effective degree of saturation, temperature, porosity, pore-gas pressure, and the rate of degree of saturation change with time for both wetting and drying processes. The model was used to fit experimental data of the FEBEX bentonite, with good agreements between measured and calculated results.

Keyword
Water retention curve, Soil-water characteristic curve, Suction, Buffer material, Drying and wetting processes, Coupled thermo-hydro-mechanical (THM) processes
National Category
Geophysical Engineering
Identifiers
urn:nbn:se:kth:diva-12056 (URN)10.1007/s11242-011-9857-z (DOI)000298296700008 ()2-s2.0-83855160869 (Scopus ID)
Note
QC 20100720. Updated from submitted to published, 20120315. Previous title: A water retention curve model for coupled thermo-hydro mechanical processes of geological porous mediaAvailable from: 2010-02-26 Created: 2010-02-26 Last updated: 2012-03-15Bibliographically approved
4. A 3D FEM simulation of the buffer and buffer-rock interfacebehaviour of the Canister Retrieval Test (CRT) at Äspö HRL: 29 Sep-01Oct 2009, Luxembourg. European Commission
Open this publication in new window or tab >>A 3D FEM simulation of the buffer and buffer-rock interfacebehaviour of the Canister Retrieval Test (CRT) at Äspö HRL: 29 Sep-01Oct 2009, Luxembourg. European Commission
2009 (English)In: Proceedings Conference of impact of THMC processes on thesafety of underground radioactive waste repositories, 2009Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents a 3D FEM model for simulating the coupled THM behaviour of the buffer and buffer-rock interface behaviour of the Canister Retrieval Test conducted at the Äspö Hard Rock Laboratory, Sweden. The effect of the interface between the canister and buffer was also included. New numerical techniques were developed for more efficient FEM formulation and equation solution, and for modeling saturated or partially saturated water flow, gas flow and heat transfer in buffer and interfaces. The numerical results compare well with the measured data, and the reasonably good agreement between simulated and measured results indicates that the coupled THM processes of buffer material can be accurately predicted by the newly developed THM model and computer code.

Identifiers
urn:nbn:se:kth:diva-12057 (URN)
Note
QC20100720Available from: 2010-02-26 Created: 2010-02-26 Last updated: 2010-07-20Bibliographically approved

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