role of water adsorption in the thermo- mechanical behavior of...

1 Laurent BROCHARD May 2nd, 2019 Clays: New Perspectives, Challenges & Opportunities

Role of water adsorption in the thermo-mechanical behavior of clays

Laurent BROCHARD

Laboratoire Navier, UMR 8205, École des Ponts, IFSTTAR, CNRS, UPE, Champs-sur-Marne, France

May 2nd, 2019

Workshop “Clays: New Perspectives, Challenges & Opportunities”

2 Laurent BROCHARD Clays: New Perspectives, Challenges & Opportunities May 2nd, 2019

1st anomaly: undrained heating experiment

•  Excessive water pressurization

Monfared, M., Sulem, J., Delage, P., & Mohajerani, M. (2011). A Laboratory Investigation on Thermal Properties of the Opalinus Claystone. Rock Mechanics and Rock Engineering, 44(6), 735–747. http://doi.org/10.1007/s00603-011-0171-4

Poromechanics

Interpretation: confined water thermal expansion higher than bulk water th. exp.

3 Laurent BROCHARD Clays: New Perspectives, Challenges & Opportunities May 2nd, 2019

2nd anomaly: drained heating experiment

•  Reversible thermal expansion excessive •  Irreversible contraction (normally consolidated clays)

αirreversible ~ -10-3 K-1 Interpretation: drainage of confined water

αreversible ~ 10-4 K-1

αminerals ~ 10-5 K-1 Interpretation: confined water is not drained

Sultan, N., Delage, P., & Cui, Y. J. (2002). Temperature effects on the volume change behaviour of Boom clay. Engineering Geology, 64(2-3), 135–145. http://doi.org/10.1016/S0013-7952(01)00143-0

4 Laurent BROCHARD Clays: New Perspectives, Challenges & Opportunities May 2nd, 2019

Objective: poromechanics capturing confinement

•  Anomalies attributed to the effects of confinement •  Usual poromechanics assumes bulk properties

Clay matrix and inclusions (10 – 100 µm)

Stacks of layers (0.1 – 1 µm)

Clay layers (~ 10 nm)

Confined water = bound water = adsorbed water

Bulk water = free water = normal water

5 Laurent BROCHARD Clays: New Perspectives, Challenges & Opportunities May 2nd, 2019

Usual interpretations are non-obvious

•  In adsorption community : confined th. exp. usually lower (e.g. Lennard-Jones in a slit pore)

solid walls

Periodic boundaries

rfs

rff e

6 Laurent BROCHARD Clays: New Perspectives, Challenges & Opportunities May 2nd, 2019

Usual interpretations are non-obvious

•  In adsorption community : confined th. exp. usually lower (e.g. Lennard-Jones in a slit pore)

•  But water is not any liquid

7 Laurent BROCHARD Clays: New Perspectives, Challenges & Opportunities May 2nd, 2019

Usual interpretations are non-obvious

•  In adsorption community : confined th. exp. usually lower (e.g. Lennard-Jones in a slit pore)

•  But water is not any liquid •  Thermal expansion is not the only fluid property

involved:

•  Undrained bulk modulus •  Undrained Biot modulus •  Confined rigidity usually > bulk rigidity

Fluid rigidity

8 Laurent BROCHARD Clays: New Perspectives, Challenges & Opportunities May 2nd, 2019

Usual interpretations are non-obvious

•  In adsorption community : confined th. exp. usually lower (e.g. Lennard-Jones in a slit pore)

•  But water is not any liquid •  Thermal expansion is not the only fluid property

involved •  Confined water is not undrained

•  Confined water is in osmotic equilibrium with free water

9 Laurent BROCHARD Clays: New Perspectives, Challenges & Opportunities May 2nd, 2019

Poromechanics and adsorption •  Thermodynamic description :

osmotic equilibrium between adsorbed and bulk phases

•  Effect on mechanics: •  Disjoining pressure Pc ≠ Pb •  Pc is affected by composition or

temperature independently from Pb

→ Ex: swelling effect due to Pc at Pb = Cst

→ Need to account for the thermodynamics of the confined fluid in the poromechanics

Pc Pb

10 Laurent BROCHARD Clays: New Perspectives, Challenges & Opportunities May 2nd, 2019

Confined behavior by molecular simulation

•  Drained ⇒ Grand Canonical Monte Carlo (long) •  Undrained ⇒ Molecular Dynamics (fast)

Saturated Na-Mnt

1W 2W

11 Laurent BROCHARD Clays: New Perspectives, Challenges & Opportunities May 2nd, 2019

Confined behavior by molecular simulation •  Observation :

•  Thermal expansion lower than for bulk water

•  Strong difference between undrained volume and number rigidity (KV ~ 2 KN)

•  Non negligible drained rigidity (Kd ~ KN)

•  Some drained thermal expansion (αs ≪αd ≲ αu)

⇒ Gibbs-Duhem not valid (confined behavior not extensive)

G-D ⇒ KV = KN and Kd = 0 and Kdαd = 0 G-D ⇒ 3 thermo-mechanical moduli for a fluid

12 Laurent BROCHARD Clays: New Perspectives, Challenges & Opportunities May 2nd, 2019

Thermodynamics of the confined fluid •  Usual fluid (Gibbs-Duhem valid): 3 moduli

•  Confined fluid (Gibbs-Duhem not valid): 6 moduli

•  Volume and number rigidities differ: KV ≠ KN •  There is a non-zero drained rigidity: Kd ≠ 0 •  There is a drained thermal-expansion: αd

13 Laurent BROCHARD Clays: New Perspectives, Challenges & Opportunities May 2nd, 2019

Revisited poromechanics •  Usual poromechanics

•  Control of the fluid pressure Pb

•  Revisited poromechanics •  Control of the fluid chemical potential µ and temperature T

…

14 Laurent BROCHARD Clays: New Perspectives, Challenges & Opportunities May 2nd, 2019

Thermal pressurization (undrained heating) •  Thermal pressurization coefficient

•  Salient features: •  No Gibbs-Duhem •  Thermo-mechanical couplings •  Double porosity

Usual poromech.

New poromech.

15 Laurent BROCHARD Clays: New Perspectives, Challenges & Opportunities May 2nd, 2019

Confrontation with experiment

•  New poromechanics captures experiment if the confined water is 2W water

•  The main origin of the anomalous pressurization is the less intuitive contribution (difference between thermal expansion at constant Pb and at constant Pc)

16 Laurent BROCHARD Clays: New Perspectives, Challenges & Opportunities May 2nd, 2019

Drained heating •  Reversible expansion: also captured by new poromechanics •  Irreversible contraction: model based on transition between

hydration states inspired by shape memory alloys (qualitative)

Brochard et al. (2017). Acta Geotechnica, 12(6), 1261. Honorio et al. (2017). Langmuir, 33(44), 12766.

17 Laurent BROCHARD Clays: New Perspectives, Challenges & Opportunities May 2nd, 2019

Conclusions •  Revisit the poromechanics of clays starting from

confined water •  Successfully reproduce THM anomalies •  Main messages

•  Confinement = more thermo-mechanical properties •  Fluid transfers between free and bound water are essential

•  Perspectives •  Explore confined fluid properties •  Extend to irreversible contraction

18 Laurent BROCHARD May 2nd, 2019 Clays: New Perspectives, Challenges & Opportunities

Thank you for your attention

Funding from the French National Research Agency (ANR) Project ‘TEAM2ClayDesicc’ (ANR-14-CE05-0023-01)

T. Honorio (postdoc)