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