The document summarizes a presentation on further important topics in rock salt geomechanics for radioactive waste repositories. It discusses three main topics: (1) how salt deforms in the long term, (2) integrity analysis of salt as a barrier, and (3) consolidation of crushed salt backfill. It provides updates on recent progress and remaining issues, including experimental work and modeling efforts. Key ongoing activities include the BMWI joint project WEIMOS and a DAEF initiative for improved modeling of crushed salt consolidation through international collaboration.

1. 7th US/German Workshop on Salt Repository
Research, Design, and Operation
Presenter: Sandra Fahland
BGR, Hannover, Germany
Washington, DC
September 7-9, 2016

2. Further Important Topics in Rock Salt
Geomechanics – State 2016
Repositories in salt formations - present and future work related to integrity analyses
 Geomechanical integrity analysis of the repository is a main topic of performance assessment
 3 main salt related topics have been identified (5th US-German Workshop 2014)
(1) how salt deforms in the long term
(2) integrity analysis of rock salt barrier
(3) consolidation of crushed salt
2
 Progress in 2015/16
 Reminder on issues still pending
 New topics

3. Salt – barrier properties
3
crushed salt
backfill -photo
Intact rock salt EDZ Crushed salt backfill

4. The challenge … how does salt behave in the
long term?
4
Boundary conditions:
Forecast period: 103 < time (years) < 106
Deformations: 0.1 < ε < 1
Deformation rates: 1∙10-17 < ε (1/s) < 3∙10-11
Temperatures: 20°C - 200°C
Experimental database
 Creep experiments at small deviatoric
stresses
 Berest (SMRI): uniaxial creep test
 BGR: running (>1 y now)
 IfG: long tests are started / a high
resolution creep test rig is under
construction
 EU Project DOPAS – LASA EDZ:
Experimental data related to
salt/concrete interfaces (GRS)
Currently pending
 Assessing the suitability of the
constitutive laws by recalculating
failure events ( KOSINA)
Forthcoming topics
 "Relaxation"
 Pressure solution creep
˙
Modelling the salt barrier behavior (THMC)
• BMWi Joint Project „Comparison of current
constitutive models for rock salt“ (2004 – 03/2016)
• BMWi Joint Project WEIMOS „Further development
and qualification of the rock mechanical modelling
for the HLW disposal in rock salt“ (WEIMOS),
started April 2016 - Partners: AH, IfG, IUB, TU-BS,
TUC, SNL
• Creep at small deviatoric stresses
• Tensile stress
• Healing of damage: influence pT
• Influence of inhomogeneities (e.g. interfaces)
Presentation
A. Hampel
Presentation
K. Wieczorek

5. Rock salt deformation behavior at small
deviatoric stresses
5
BGR (2016)
Varangeville - Berest et al. (2015): Avery Island salt
Dead weight setup

6. Natural analogues – closing the gap?
6
3D-simulation of salt dome uplift
Subgrain – paleostress analysis
"dry" salt
dome
• In different salt structures, deformation
mechanisms and rheology may be different.
• Microstructure analysis is required to study
deformation mechanisms, paleostress and
paleorheology.
• Numerical modelling allows demonstration.
"humid"
bedded
salt
"wet" salt
glacier
Residual stress?

7. Subgrain – paleostress analysis; Gorleben salt dome,
Germany
7
subgrains and paleostresses in halitic rocks in
central part of salt dome (Hauptsalz, Staßfurt-
Series, z2HS)
(Hammer et al. 2015, Thiemeyer et al. 2016)
subgrains and paleostresses in halitic rocks
near intensively deformed anhydrite rocks in
salt dome (Anhydritmittelsalz, Leine-Series, z3AM)
(Mertineit et al. 2015)

8. The WEIMOS approach: High-resolution creep rig
of IfG
8
Axial force: 200 kN
Sample size:
 = 60mm,
l = 120mm
Capacitive displacement
system
Quartz rod
CSH02FL-CRm1,4
Resolution 0.15 nm
Linearity 0,05 m
Temperature sensitivity -2.4 nm/°C
Measuring principle
The principle of capacitive displacement
measurement using the capaNCDT (capacitive
Non-Contact Displacement Transducer)
system is based on how an ideal plate-type
capacitor operates. The two plate electrodes are
represented by the sensor and the opposing
measurement object.
Pc-max: 32 MPa
Tmax: 120°C

9. Integrity of the salt barrier
9
Criteria to assess integrity are decisive to prove effectiveness of salt barrier’s safety function
Present status
 dilatancy criterion
(isotropic)
 minimum stress/fluid
pressure criterion
(isotropic)
Under consideration
 load-dependent dilatancy criterion
(BGR)
 anisotropic fluid pressure criterion,
directional infiltration (THM process)
- TUC/IfG/BGR/DBETEC
 The dihedral angle – An additional
percolation threshold? Science
paper „Deformation-assisted fluid
percolation in rock salt“ by S.
Ghanbarzadeh et al.
 DAEF – statement April 2016
 Break-out-session US/German
Workshop 2016
 KOSINA: Percolation tests at high
pT cond. (-100 MPa/120°C)
First steps/pending
 discontinuum
approaches
 DBETEC, IfG
 Fully coupled thermo-
hydro-mechanical
simulations
 TUC, IfG
Forthcoming topics
 additional
(hypothetical) failure
modes TUBS, DBETEC
 influence of residual
stresses

10. Additional (hypothetical) failure modes
10
Isotropic fluid pressure criterion
σmin > pfl
using effective stresses (Terzaghi)
σ‘min = σmin – pfl > 0
σmin = σ3 least principal stress
pfl = hypothetical hydraulic pressure
σ‘min = σ‘3 effective least principal stress
Isotropic dilatancy criterion (Christescu/Hunsche)
τzul/σ* = a · (σm/ σ*)² + b · (σm/ σ*)
using effective stresses (Terzaghi)
τ‘zul/σ* = a · (σ‘m/ σ*)² + b · (σ‘m/ σ*)
τ octahedral shear stress
σm mean stress
σ* scaling factor
τ‘ effective octahedral shear stress
σ‘m = (σ1 + σ2 + σ3 – 3pfl)/3 effective mean stress
properties of a viscous solid properties similar to a suspensionvs

11. Crushed salt consolidation
11
Current knowledge gives confidence that granular salt will compact to a final porosity in the
order of 1±1 % within less than 1000 a,
but this has to be demonstrated reliably
Experimental investigations
REPOPERM II long-term tests (4 y)
finished (GRS, final report in
preparation)
Long-term compaction tests (up to
10 y), BGR develops a new
experimental setup
Crushed salt backfill in-situ
consolidation state re-investigated
after 15 y in the framework of the
Asse site investigations (IfG)
State of constitutive models
DAEF initiative on crushed salt
behavior is established
First results
2-phase-flow (to appear, GRS)
Pending
Natural analogues

12. Salt consolidation lab experiments in the
REPOPERM project
12
(rawdata)
brine
injection
REPOPERM II
Multistep load tests, different initial solution contents, varying temperature, later flooding
characterization after
dismantling yields
porosities of 1 – 2%

13. Revisitation of the BAMBUS site –
part of Asse site investigations
13
 Backfill compaction proceeds: Within 15
years, a further reduction of backfill
porosity by 3 – 5% is observed ( drift
convergence at the 800‐m‐level).
 The backfill is very dry.
Aim of investigations
 Evaluation of the backfill properties
 Better assessment of stabilization
measures in the Asse repository
 Texture and lab investigations were
performed by Sandia (Hansen, 2016)
• Porosity: 23 – 17%
• Thermal conductivity: 2.3 W/m∙K
• Gas permeability: ca. 5 ∙ 10-13 m2

14. DAEF initiative on crushed salt consolidation
14
Partners:
 GRS, BGR, DBETEC, IfG, TUC
 Participation of the US-colleagues is
highly desirable
Current knowledge gives confidence that granular salt will compact to a final porosity in the
order of 1±1 % within less than 1000 a, but this has to be demonstrated reliably!
Work topics
• Classification of the available experimental data
sets:
 reliability in the low porosity range
 suitability for model calibration
• Recommendations for completing the data base
• Comparison of available constitutive models
• Development of a strategy for calibration, bench
marking and improvement of models
Work schedule
 Presentation at the DAEF-Workshop 2016
 Summary (NEA) report until 10/2016
 Preparation of an US/GERMAN joint project
proposal until the end of the year

15. Summary
Repositories in salt formations - present and future work related to integrity analyses
 Geomechanical integrity analysis of the repository is a main topic of PA
 3 main salt related topics have been identified (5th US-German Workshop 2014)
(1) how salt deforms in the long term
(2) integrity analysis of rock salt barrier
(3) consolidation of crushed salt
 Progress in 2015/16 and remaining open issues
Ongoing key activities
• BMWI - Joint Project (WEIMOS), started April 2016
Several experiments are already running or planned
• Percolation – experimental proof at repository conditions
• DAEF initiative on crushed salt behavior established - US/German collaboration discussed
15

16. Acknowledgements
16
Many thanks…
…to all colleagues and participating organizations
for their contributions
and BMUB and BMWi and their related organizations for their financial support.