| 1. |
- Baud, Patrick, et al.
(författare)
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The Brittle-Ductile Transition in Porous Limestone : Failure Mode, Constitutive Modeling of Inelastic Deformation and Strain Localization
- 2021
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Ingår i: Journal of Geophysical Research: Solid Earth. - 2169-9313. ; 126:5
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Tidskriftsartikel (refereegranskat)abstract
- Understanding of the mechanics of the brittle-ductile transition (BDT) in porous limestone is significantly more challenging than for sandstone because of the lack of consistent acoustic emission activity in limestone, meaning that one must rely on alternative techniques. In this paper, we investigate systematically the failure modes in Indiana limestone using X-ray microComputed Tomography imaging (μCT) and Digital Volume Correlation (DVC). Our new mechanical data show that the envelope for the onset of shear-enhanced compaction can be well approximated by an elliptical cap. The DVC analysis revealed the development of shear bands through the BDT, but no evidence of compaction bands. The shear band angles were between 29° and 46° with respect to the maximum principal stress. Compiling these new results with published data on Purbeck and Leitha limestones, we showed that inelastic compaction in each of these dual porosity allochemical limestones was in a good agreement with the normality condition, as defined in plasticity theory. Comparison of the observed failure modes with predictions based on bifurcation analysis showed that the shear band angles are consistently smaller than the theoretical predictions.
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| 2. |
- Baud, Patrick, et al.
(författare)
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The Brittle-Ductile Transition in Porous Limestone Imaged by X-Ray Computed Tomography and Digital Image Correlation
- 2017
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Ingår i: Poromechanics 2017 - Proceedings of the 6th Biot Conference on Poromechanics. - Reston, VA : American Society of Civil Engineers. - 9780784480779 ; , s. 1782-1788
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Konferensbidrag (refereegranskat)abstract
- We studied the brittle-ductile transition in three porous carbonates, Indiana, USA, Majella, Italy, and Leitha, Austria, with porosity ranging between 16 and 31%. A series of triaxial experiments were performed at room temperature, constant strain rate, and at effective pressures ranging from 5 to 150 MPa. Several sets of X-ray Tomography images were acquired before and after deformation. 3D digital image correlation (DIC) was performed on the images of the intact and deformed samples. The use of 3D-volumetric DIC allowed us to map out the subtle development of strain localization associated with the transition from brittle faulting to cataclastic flow in the three limestones. Our observations showed that strain localization may develop at relatively small axial strains of ~1%, in both the brittle faulting and transitional regimes. In Majella limestone (porosity = 31%), the localized deformation involved both shear and compaction. Compaction bands were only observed in less cemented samples of Leitha limestone.
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| 3. |
- Ji, Yuntao, et al.
(författare)
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Characterization of pore structure and strain localization in Majella limestone by X-ray computed tomography and digital image correlation
- 2015
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Ingår i: Geophysical Journal International. - : Oxford University Press (OUP). - 0956-540X .- 1365-246X. ; 200:2, s. 699-717
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Tidskriftsartikel (refereegranskat)abstract
- Standard techniques for computed tomography imaging are not directly applicable to a carbonate rock because of the geometric complexity of its pore space. In this study, we first characterized the pore structure in Majella limestone with 30 per cent porosity. Microtomography data acquired on this rock was partitioned into three distinct domains: macropores, solid grains, and an intermediate domain made up of voxels of solid embedded with micropores below the resolution. A morphological analysis of the microtomography images shows that in Majella limestone both the solid and intermediate domains are interconnected in a manner similar to that reported previously in a less porous limestone. We however show that the macroporosity in Majella limestone is fundamentally different, in that it has a percolative backbone which may contribute significantly to its permeability. We then applied for the first time 3-D-volumetric digital image correlation (DIC) to characterize the mode of mechanical failure in this limestone. Samples were triaxially deformed over a wide range of confining pressures. Tomography imaging was performed on these samples before and after deformation. Inelastic compaction was observed at all tested pressures associated with both brittle and ductile behaviors. Our DIC analysis reveals the structure of compacting shear bands in Majella limestone deformed in the transitional regime. It also indicates an increase of geometric complexity with increasing confinement-from a planar shear band, to a curvilinear band, and ultimately to a diffuse multiplicity of bands, before shear localization is inhibited as the failure mode completes the transition to delocalized cataclastic flow.
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| 4. |
- Wu, Lele, et al.
(författare)
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Organic matter composition and stability in estuarine wetlands depending on soil salinity
- 2024
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Ingår i: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 945
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Tidskriftsartikel (refereegranskat)abstract
- Coastal wetlands are key players in mitigating global climate change by sequestering soil organic matter. Soil organic matter consists of less stable particulate organic matter (POM) and more stable mineral -associated organic matter (MAOM). The distribution and drivers of MAOM and POM in coastal wetlands have received little attention, despite the processes and mechanisms differ from that in the upland soils. We explored the distribution of POM and MAOM, their contributions to SOM, and the controlling factors along a salinity gradient in an estuarine wetland. In the estuarine wetland, POM C and N were influenced by soil depth and vegetation type, whereas MAOM C and N were influenced only by vegetation type. In the estuarine wetland, SOM was predominantly in the form of MAOM ( > 70 %) and increased with salinity (70 % -76 %), leading to long-term C sequestration. Both POM and MAOM increased with SOM, and the increase rate of POM was higher than that of MAOM. Aboveground plant biomass decreased with increasing salinity, resulted in a decrease in POM C (46 % - 81 %) and N (52 % -82 %) pools. As the mineral amount and activity, and microbial biomass decreased, the MAOM C (2.5 % -64 %) and N pool (8.6 % -59 %) decreased with salinity. When evaluating POM, the most influential factors were microbial biomass carbon (MBC) and dissolved organic carbon (DOC). Key parameters, including MBC, DOC, soil salinity, soil water content, aboveground plant biomass, mineral content and activity, and bulk density, were identified as influencing factors for both MAOM abundance. Soil water content not only directly controlled MAOM, but together with salinity also indirectly regulated POM and MAOM by controlling microbial biomass and aboveground plant biomass. Our findings have important implications for improving the accumulation and increased stability of soil organic matter in coastal wetlands, considering the global sea level rise and increased frequency of inundation.
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