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On the hydro-mechanical behaviour of unsaturated damaged Callovo-Oxfordian claystone
Abstract During the excavation of drifts within the French Underground Research Laboratory (URL) in the Callovo-Oxfordian claystone (COx) formation, an excavation damaged zone (EDZ) was formed, which is expected to have adverse effects on the long-term safety of the radioactive waste repository. In this study, high pressure oedometer tests with controlled suction were performed to investigate the hydro-mechanical behaviour of damaged COx claystone. The hydraulic conductivity was measured under different vertical stresses. The suction and damage effects were analysed in terms of swelling, compression, hydraulic conductivity and creep. Besides, the evolution of micro-cracks inside the damaged claystone sample was also analysed through X-ray computed tomography (CT) and Mercury intrusion porosimetry (MIP). The oedometer results indicate that the damaged claystone has a lower swelling strain than the intact one, due to the effect of macro-pores created by damage. The damaged claystone with a higher suction exhibits a lower compressibility and larger yield stress. There is a linear correlation between hydraulic conductivity and vertical stress at zero suction. Compared with the intact claystone, the damaged one presents a lower compression index C c. Besides, step compression index C c* and secondary consolidation coefficient C α both increase with the increase of vertical stress and with the decrease of suction, indicating the dependence of the compression and creep behaviours on stress and suction. A satisfactory linear relationship is observed between C α and C c* at each suction and the corresponding slope depends on suction. Microstructure observations from CT and MIP tests show that the micro-cracks inside the damaged sample after loading are more significant with the increase of suction, suggesting that the micro-cracks were closed more easily by loading at a lower suction. A damaged coefficient was identified to quantitatively analyse the evolution of micro-cracks.
Highlights The swollen clay minerals filled the preexisting micro-cracks, leading to a decrease of the swelling potential. The compression and creep behaviours depend on stress and suction. A key stress 16 MPa is related to the closure of micro-cracks and grain breakage. The micro-cracks became more significant with the increase of suction after oedometer compression.
On the hydro-mechanical behaviour of unsaturated damaged Callovo-Oxfordian claystone
Abstract During the excavation of drifts within the French Underground Research Laboratory (URL) in the Callovo-Oxfordian claystone (COx) formation, an excavation damaged zone (EDZ) was formed, which is expected to have adverse effects on the long-term safety of the radioactive waste repository. In this study, high pressure oedometer tests with controlled suction were performed to investigate the hydro-mechanical behaviour of damaged COx claystone. The hydraulic conductivity was measured under different vertical stresses. The suction and damage effects were analysed in terms of swelling, compression, hydraulic conductivity and creep. Besides, the evolution of micro-cracks inside the damaged claystone sample was also analysed through X-ray computed tomography (CT) and Mercury intrusion porosimetry (MIP). The oedometer results indicate that the damaged claystone has a lower swelling strain than the intact one, due to the effect of macro-pores created by damage. The damaged claystone with a higher suction exhibits a lower compressibility and larger yield stress. There is a linear correlation between hydraulic conductivity and vertical stress at zero suction. Compared with the intact claystone, the damaged one presents a lower compression index C c. Besides, step compression index C c* and secondary consolidation coefficient C α both increase with the increase of vertical stress and with the decrease of suction, indicating the dependence of the compression and creep behaviours on stress and suction. A satisfactory linear relationship is observed between C α and C c* at each suction and the corresponding slope depends on suction. Microstructure observations from CT and MIP tests show that the micro-cracks inside the damaged sample after loading are more significant with the increase of suction, suggesting that the micro-cracks were closed more easily by loading at a lower suction. A damaged coefficient was identified to quantitatively analyse the evolution of micro-cracks.
Highlights The swollen clay minerals filled the preexisting micro-cracks, leading to a decrease of the swelling potential. The compression and creep behaviours depend on stress and suction. A key stress 16 MPa is related to the closure of micro-cracks and grain breakage. The micro-cracks became more significant with the increase of suction after oedometer compression.
On the hydro-mechanical behaviour of unsaturated damaged Callovo-Oxfordian claystone
Wang, Hao (author) / Cui, Yu-Jun (author) / Vu, Minh Ngoc (author) / Zhang, Feng (author) / Talandier, Jean (author)
Engineering Geology ; 319
2023-03-28
Article (Journal)
Electronic Resource
English
Investigation into the compression behaviour of unsaturated damaged Callovo-Oxfordian claystone
| DOAJ | 2023
Poroelasticity of the Callovo–Oxfordian Claystone
| British Library Online Contents | 2017