role of water adsorption in the thermo- mechanical behavior …...laurent brochard clays: new...

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.


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


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


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




•  But water is not any liquid




•  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




•  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


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


Confined behavior by molecular simulation

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

Saturated Na-Mnt

1W 2W


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


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


Revisited poromechanics •  Usual poromechanics

•  Control of the fluid pressure Pb

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

…


Thermal pressurization (undrained heating) •  Thermal pressurization coefficient

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

Usual poromech.

New poromech.


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)


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.


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)

role of water adsorption in the thermo- mechanical behavior …...laurent brochard clays: new...

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