Earth Sciences Division (ESD) Department of Energy (DOE) Lawrence Berkeley National Laboratory (LBNL)

The UFD Campaign:  UFD Natural Systems Research

Coupled process modeling

An argillaceous rock responds to changes in thermal, chemical, mechanical, and hydrological conditions in a complex way. The opening of the tunnel results in immediate changes in mechanical stress in the surrounding rock. Subsequent ventilation results in partial drying of the rock and the introduction of oxygen. These processes cause the formation of fractures in an excavation disturbed zone around the drift. After waste emplacement and closure, the rock is subject to the chemical effects of emplaced materials and mechanical stresses generated by resaturation and swelling of the rock as well as swelling of bentonite backfill inside the tunnel. Finally, the waste produces heat changing the temperatures in the near-drift zone. Argillaceous rock is subject to these processes in complex, coupled relationships. Thermal effects cause changes in chemistry and mechanical stress, mechanical stress and chemical reactions affect hydrologic properties, and hydrologic processes transport dissolved solutes and heat. One of the special characteristics of an argillaceous rock is the sensitivity of mechanical stress (swelling) to water composition, producing stronger coupled effects between chemical and mechanical processes than in many other rock types.

 

Current activities concerning coupled processes are the following:

Thermal-hydrological-mechanical processes (LBNL Contact:  Jonny Rutqvist (see contact information below)) 

Investigations have focused on the effects of water evaporation, and volume shrinkage/swelling on initiation and development of the disturbed rock zone around repository excavations in argillaceous rock. Relationships have also been investigated between shrinkage effect, anisotropic properties caused by bedding structures, stress-dependent deformability of clay and the effects of elasto-plastic behavior.

 

minimum principle stress using linear elastic constitutive model minimum principle stress using nonlinear elasto-plastic constitutive model

minimum principle stress using linear elastic constitutive model

minimum principle stress using nonlinear elasto-plastic constitutive model

 

Thermal-hydrological-chemical processes (LBNL Contact:  Liange Zheng (see contact information below)) 

The effects of geochemically-induced swelling and shrinkage have been investigated for argillaceous rock. The swelling-property changes in a saturated clay rock are mostly due to the geochemical changes, including (1) changes in ion concentration of the bulk water, which may also change the swelling properties; (2) cation exchange changes in the composition of the water in the interlayer space, and therefore changes in the swelling of the rock and (3) swelling minerals such as smectite may dissolve (for example, as the pH increases) or precipitate (due to the dissolution of silicates), which subsequently modify the swelling of the rock. A swelling model based on the Gouy-Chapman DDL theory has been adopted to evaluate the changes in swelling properties for near-field repository argillaceous rock.

 

Radionuclide transport in natural system is affected by couple processes

(Liu et al., 2011)


 Thermal-hydrological-mechanical-chemical processes (LBNL Contact:  Jonny Rutqvist and Liange Zheng (see contact information below)) 

These investigations have focused on the development of a numerical simulation tool that can address simultaneous coupling between thermal, hydrological, chemical, and mechanical processes for an argillaceous rock environment.

Thermal-hydrological-mechanical-chemical processes

   
 Constitutive relationships for coupled processes (LBNL Contact:  Hui-Hai Liu (see contact information below)) 

These investigations have focused on the development of a constitutive model for nonlinear stress-strain behavior and how hydraulic and mechanical rock properties are affected by the new constitutive model.

Matches between results calculated from nonlinear stress-strain model

Matches between results calculated from nonlinear stress-strain model (Liu et al., 2011) and experimental data from unconfined compression tests on clay rock (Corkum and Martin, 2007)

 

For more information, please contact:

Name Title ESD Department Phone Fax Email
Jonny Rutqvist Staff Scientist Hydrogeology Department 510-486-5432 510-486-5686 JRutqvist@lbl.gov
Liange Zheng Staff Scientist Hydrogeology Department 510-486-5502 510-486-5686 LZheng@lbl.gov
Hui-Hai Liu Staff Scientist Hydrogeology Department 510-486-6452 510-486-5686 HHLiu@lbl.gov