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Author:Kajanto, Karita
Title:The effect of stress state on groundwater flow in bedrock - simulations of in situ experiments
Jännitystilan vaikutus pohjaveden virtaukseen kallioperässä - paikkatutkimustulosten mallinnusta
Publication type:Master's thesis
Publication year:2013
Pages:[7] + 51      Language:   eng
Department/School:Teknillisen fysiikan laitos
Main subject:Ydin- ja energiatekniikka   (Tfy-56)
Supervisor:Salomaa, Rainer
Instructor:Pulkkanen, Veli-Matti
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  4   | Archive
Keywords:permeability
stress
in situ
bedrock
groundwater
permeabiliteetti
jännitystila
in situ
kallioperä
pohjavesi
Abstract (eng): The effect of the stress state on the permeability of bedrock for groundwater was studied by simulating an in situ experiment.
Previous studies show that the dependency of permeability on stress can have a significant effect on flow.
Several models have been developed, but little has been done in order to develop models suitable for in situ applications, such as the deep underground repositories for spent nuclear fuel.
In repositories, stress state evolves during the long time period considered in safety assessment.
The effect of the changing flow pattern, due to the evolving stress, has to be estimated for, e.g., radionuclide transport calculations.

Previous work done in the field was reviewed, existing relations between stress and permeability were analysed, and suitable relations were selected for the modeling cases.
Rock mass permeability and discrete fracture permeability were treated separately.
One new empirical model for fracture permeability was presented and three models were further developed to be more suitable for 3-D implementation.
Simulations followed in situ experiments conducted in Äspö Hard Rock Laboratory.

The modelling geometry was constructed based on the experimental setup and the fracture information from the location.
The overall stress state in the area was known and the effect of the measurement tunnel and boreholes was computed.
The stress state was used to compute the groundwater flow, and the applicability of the chosen models for in situ modelling was analysed.
COMSOL Multiphysics was used as the tool for the simulations.

The simulation results followed the measurements reasonably well, but differences were found with one model.
The results show that differences between most of the models were relatively small if in flow rates were compared, however, differences between flow patterns were found.
Stress dependency could partly explain observed phenomena and qualitative behaviour.
Moreover, some of the fracture models were able to identify fractures prone to deformation.
Abstract (fin): Jännitystilan vaikutusta kallioperän permeabiliteettiin vedelle tutkittiin simuloimalla in situ -tilannetta.
Aiemmat tutkimukset ovat osoittaneet, että permeabiliteetin riippuvuus jännitystilasta voi vaikuttaa merkittävästi kallion pohjavesivirtaukseen.
Erilaisia malleja aiheesta on kehitetty, mutta in situ -mallinnukseen soveltuvien mallien kehitys on jäänyt vähemmälle.
Turvallisuusanalyysin pitkän ajanjakson aikana jännitystila kalliossa loppusijoitussyvyydellä muuttuu.
Muuttuvan jännityksen virtaukseen aiheuttamat muutokset tulee ottaa huomioon radionuklidien kulkeutumislaskennassa.

Tässä työssä käytiin läpi alan aiempia tutkimuksia, analysoitiin kehitettyjä jännityksen ja permeabiliteetin välisiä malleja sekä valittiin erilaisia tutkittavalle kivityypille soveltuvia malleja mallinnustapauksissa käytettäviksi.
Kiviaineksen permeabiliteettia ja yksittäisten rakojen permeabiliteettia käsiteltiin erikseen.
Uusi empiirinen rakopermeabiliteettimalli esiteltiin ja aiempia malleja kehitettiin paremmin in situ -mallinnukseen sopiviksi.
Simulaatiotapaukset laadittiin Äspö Hard Rock Laboratoryssa tehtyjen mittausten mukaisesti.
Laskentageometria vastasi koejärjestelyjä ja alueelta tehtyjä havaintoja.
Alueen keskimääräinen jännitystila tunnetaan, ja sen avulla laskettiin mittaustunnelin ja reikien vaikutus mallinnusalueella.
Valittujen mallien soveltuvuutta in situ -mallinnukseen analysoitiin.
Laskenta suoritettiin COMSOL Multiphysics -ohjelmistolla.

Mallien tulokset noudattivat mittauksia in situ -mallinnustuloksiksi hyvin, mutta joissain tapauksissa esiintyi selviä eroja.
Virtaamatuloksien väliset erot useiden mallien kesken olivat suhteellisen pieniä.
Virtausjakaumista löytyi selkeitä eroja, ja jännitystilariippuvuudella voinee selittää joitain tuloksia ja käyttäytymistä.
Lisäksi havaittiin, että eräillä rakomalleilla pystyy tunnistamaan raot, joilla on muita suurempi todennäköisyys deformaatioon.
ED:2013-09-05
INSSI record number: 47165
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