summary report of the clay workshop theresa – timodaz workshop luxembourg 30 sept. – 1st oct....

Summary report of the Clay Workshop

THERESA – TIMODAZ WorkshopLuxembourg 30 Sept. – 1st Oct. 2009

Starting point… background fromEDZ conference & WS 2003

– Focus on EDZ– Long-term THMC behaviour was not deeply discussed

• Scale effects• EDZ:

– Complexity of EDZ– Mecanisms of sealing– Evolution of the EDZ during the thermal phase– EDZ role as a pathway for gas release

• Long-term geochemical evolution– GDZ extent?

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Objectives for the WG clay…• A 2009 "Update": table describing the sequence of FEPs

driving the evolution of the near-field of repository system– Involved processes– Modelling issues– Uncertainties/knowledge gaps– Relevance for PA– Need for experimental data– Need for model/code development

Including THMC processes & mechanisms

Reported here as "achievements" (/2003) & "open issues"

• An expert judgement exercice– 2 test cases

• Indurated Clay• Plastic Clay

Four time-periods considered

• P1 – Disposal gallery construction– from front excavation to a few days after lining installation

• P2 – Waiting time - gallery ventilation– from lining installation to waste/backfill installation

• P3 – Exploitation period– from waste/backfill installation to repository closure

• P4 – Post-closure period

P1 – Disposal gallery construction

from front excavation to a few days after lining installation

P1 – Achievements since 2003Open issues

In situ experiments

• SELFRAC, NFPRO results

• Progress about in situ caracterisation: – Ultrasonic methods: damage and afterwards rock consolidation

observed (cf. Schuster et al)– But probably not exhaustive

• Difficult to have experimental data on the onset of fracture development and opening (also for lab tests)


HM Processes

• Pore pressure:– Effectiveness of the poromechanical framework both for PC & IC– Increase/decrease, depending on the location and distance from the drift– Decrease can even reach suction for “large” volumetric strain (positive

effect for self-support, as long as the rock can handle such suction)– Underestimation of hydraulic disturbance : further investigation needed

(anisotropy, viscous effects, …). Not directly important for EDZ but important issue for confidence – Need to look at small deformation

• Suction:– Important issue: suction evolution within the damage zone– Importance of entry pressure value (link with desaturation)


HM Processes (cont.)

• EDZ – Shear fractures (slick + sliding)– But also other fractures types (tensile)

• Important aspects / EDZ– Amount of opening– Scale aspects (micro/macro)– Interconnectivity (difference EDZ/EdZ)– Different processes occur in saturated zones (increase pore

pressure) w.r.t. desaturated ones (see Modelling)


HM Processes (cont.)

• Rock intrinsic behaviour:– Importance of anisotropy (at least elastic, plastic ),– Importance of OCR (at least for PC)

• We now live in 3D “world”– Stress paths while excavating drift not as simple as expected– “Material” is no longer the same ahead the excavated front and

around the gallery (≠ stress paths, ≠ damage)

• Upscaling aspects...

• Pre-existing discontinuities?


Modelling (accepted concepts)

• In 2003, we lived in an isotropic, axisymmetric world

• In 2009, the world is truly 3D, heterogeneous, anisotropic– Progress HM coupling taking into account elastic anisotropy…– Able to model the width of HDZ (not the amplitude)– Local variation of the in situ stress field due to excavation (e.g.

pillar effect that may lead to principal stress permutations)– Simulation of advancing excavation front important to study the

interconnectivity around gallery

• Key role of initial conditions, initial rock state

P1 – Achievements since 2003 Open issues

Modelling (cont.)

• Multiple, complementary approaches (elastic damage, plasticity), discrete (??), damage threshold (? or ?)

• Models/simulations of K evolution:– Still lack of validation w.r.t. real situations

• Micromechanics:– Micro-mechanics based-models used to simulate true structure

problems, ongoing...– Need for texture description at relevant scale(s)?

P1 – Achievements since 2003 Open issues

Modelling (cont.)

EDZ modelling:• Diffuse damage modelling (K predicted from physical

basis) • Towards and after localisation with existing

discontinuities??)– “Potential” progress in numerical techniques – localisation –

XFEM – (water flow through discontinuities?) - But lack of practice

– Interactions between discontinuties still seems a serious challenge

P2 – Waiting time - gallery ventilation

from lining installation to waste/backfill installation

(Several months to several years)


HM Processes

• Water retention properties • Ventilation– Need to consider the physical basis/meaning of the hydric boundary

condition (net water flux towards drift non equilibrium)– Exchanges conditions at the boundary– Suction ≠ desaturation• Time-dependent deformation– For PC: recognized as mostly creep– For IC: sub-critical crack growth as an other candidate deformation

mechanism? Ongoing– Expected different time scales… Ongoing


In situ experiments

• SELFRAC, NFPRO results• Input from experimental data (6 years more data existing

database increase)• Progress in situ:

– Ultrasonic methods: damage and afterwards rock consolidation observed

• Effectiveness of sealing – Observed (also in lab test) when saturating fluid = water– Still effective for more natural resaturation paths (i.e. limited

available water fluxes)?


CHM Processes

• Osmotic flux due to salt gradient (Mt Terri - negligible)• Characteristic time of the CM coupling?• Importance of organic matter • Presence of sulphides in the rocks:

– Oxidation to sulphates looks harmful (H2S): – Concentration profiles similar for old and new gallery process

linked to excavation (also linked to the support type)– Microbiological activity: stop to be active (but should be

investigated more)– Most probably has limited influence as there is no real flow


Modelling

• Modelling of delayed effects has to take into account:

– Pore pore pressure dissipation– Clay matrix sliding at clay particles or platelets level

(viscoplasticity)• Desaturation inhibited

– Subcritical micro-crack propagation (differed damage)• Desaturation enhanced

– Need for multi-scale modelling (nano, micro, meso)


Uncertainties / Knowledge gaps

• Realistic rock properties:– Limitation of lab test to determine the time dependent

parameters: short period of time compared with the actual process

lead to overestimate TD behaviour

• Lab techniques to compensate the short time-period of the tests – (e.g. thermal or cyclic loads)


Relevance for PA

• Q1: Fracture will start to close from the far field to the lining (depending on water supply for IC)

• Q2: Fracture could even partially recover the characteristics of undamaged matrix (essentially in term of hydraulic properties)

• May go in one direction or the other one depending on many factors: – the swelling properties, – the water supply, highly design dependent– the ventilation, – the type of support, …


Predictives cap. / Need for model dev.

• Discussion... divergent/complementary view points:

– Model capacities are fine, but more data are needed

– Interface behaviour still requires more development

– Need to go to multi-scale modelling – physically-based models

P3 – Exploitation period

from waste/backfill installation (T°) to repository closure


Lab tests• Lab simulation tests EPFL• UPC test (see poster)

– More controlled lab tests boundary conditions– Similar feature than in situ

In situ tests• Small scale in situ tests (TER, HED ATLAS)

– Increase confidence to the physical model and credit to the predictive modelling capacity

– Allows a lot of comparisons– Thermo-plastic (Damage) – recent development

• Missing experiments:– To get hydraulic fracturation (determination of fracturation limit)– With several heaters (more realistic wrt disposal)


THM Processes• Coupling with desat

– increase of desaturated zone (air present in the buffer decrease heat conductivity)

• Coupling with damage– Fracture developement– Thermally induced damage: indicators from bonding tests (e.g. HED

experiment)– Thermal effect on damaged rock and not on intact material

• Combined effect of desaturation and T° increase• THM coupled response is strongly dependent on rock type and boundary

conditions (design) either: – Increase damage– Enhance sealing– Interfaces with EBS important


Modelling (THM)

• More time needed to be confident in THM behaviour – No clear idea about the performance of the models even progress was made

• Drained data crucially lacking (TIMODAZ?)• Data needed for time-dependent behaviour• Drained / undrained conditions to be further investigated

(better terminology "No flow/ flow" water BC?)• Intrinsic test difficult to achieve:

– Test at ≠ scales. – Interaction/iteration with modelling to interpret them


Uncertainties / Knowledge gaps

• Field thermal conductivity anisotropy – heat flow in a preferential direction– Simple parameter, but not as easy to determine

• Uncertainties EBS: – density/swelling, interface behaviour (e.g. gap) EBS/lining/host-

rock design optimisation (e.g. pellets)

P4 – Post-closure period


Long term THMC Processes

• Alkaline plume around concrete-based components– More confident on its limited impact.– The difficulty lies in comparing against real data (hardly possible

because very long processes)

• Natural analog (not so easily to define)– More confirmation than validation


Modelling

• For long term simulation– Outer boundary conditions will have influence (top & bottom)– Multiscale models (µ-mechanics) may lead to some theoretical

bounds (e.g. work currently performed in Andra R&D programme)

• Lack of data to validate models– Sensitivity analyses could be helpful

Common to P1-P4

Common achievements since 2003 Open issues

Lab. experiments

• Careful sampling and core conditionning• Sound experimental protocols (e.g. initial consolidation)• Intrinsic tests (direct determination of constitutive model

parameter values):– Required ideally, but… not easy for low K materials (with

heterogeneous fields: Pp, Sig…)– A workaround: need for an integrated experimentation/modelling

approach (lab tests must be interpreted as true structure with its Init.Cond. and Bound.Cond.)

• Need for local Pp measurements

Common achievements since 2003 Open issues

Lab. experiments (cont.)

• Visualisation possibilities (e.g., x-ray CT)– Initial sample states, damage visualisation

lead to new questions– Still a need to have good samples and experimental protocol– Storage conditionning importance for experiments and

modelling– Visualisation possibilities (e.g., x-ray CT)

• Simulation tests (physical, scale model)– Hollow cylinder…– Decrease the size of the drainage length

To conclude… are we far from minimum target? The remaining difficult points

For Phase 1• EDZ in situ full picture • Modelling strategies for localisation, interaction• Behaviour law to account for damagePhase 2• Sub-µCrackProp (i.e. differed damage) under investigation as

a potential additionnal mechanism for time-dependent deformation

Phase 3• Remaining work (lab+in situ+modelling) on THM aspects-

couplings (DZ, fractures, saturation, strength)Phase 3-4• Reliabilty of extrapolating the time-dependent behaviour to LT

(no classical lab test available)• Theoretical approaches? (µ-mech, DM…)

Expert judgement exercice

Expert judgement exercice

• Qualitative description of the expected evolution of key state variables and properties at selected locations around a disposal gallery

• Objectives were twofold:– Two different expert teams predict the same

qualitative behaviour of a disposal system?– How the knowledge acquired by scientists can

be applied to a concrete case?

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0,1 1 10 100 1000 10000 100000

Time (years)T1 T2 T3 T4T0

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Plastic Clay

Concrete? ? ?

1m 5m 20m250 m

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Different pore water pressure response in the far fieldDifferent assumptions on anisotropy (not specified in the test case)

U (MPa)

The global predicted evolution is in agreement for the two expert groups

Different thermal response in the near field

summary report of the clay workshop theresa – timodaz workshop luxembourg 30 sept. – 1st oct....

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