This study presents a fully coupled thermo-hydro-mechanical (THM) constitutive model for clay rocks. The model is formulated within the elastic-viscoplasticity framework, which considers nonlinearity and softening aft...This study presents a fully coupled thermo-hydro-mechanical (THM) constitutive model for clay rocks. The model is formulated within the elastic-viscoplasticity framework, which considers nonlinearity and softening after peak strength, anisotropy of stiffness and strength, as well as permeability variation due to damage. In addition, the mechanical properties are coupled with thermal phenomena and accumulated plastic strains. The adopted nonlocal and viscoplastic approaches enhance numerical efficiency and provide the possibility to simulate localization phenomena. The model is validated against experimental data from laboratory tests conducted on Callovo-Oxfordian (COx) claystone samples that are initially unsaturated and under suction. The tests include a thermal phase where the COx specimens are subjected to different temperature increases. A good agreement with experimental data is obtained. In addition, parametric analyses are carried out to investigate the influence of the hydraulic boundary conditions (B.C.) and post-failure behavior models on the THM behavior evolution. It is shown that different drainage conditions affect the thermally induced pore pressures that, in turn, influence the onset of softening. The constitutive model presented constitutes a promising approach for simulating the most important features of the THM behavior of clay rocks. It is a tool with a high potential for application to several relevant case studies, such as thermal fracturing analysis of nuclear waste disposal systems.展开更多
This study investigates the impact of bedding plane orientation on sodium chloride(NaCl)precipitation in a calcarenite stone,subjected to salt weathering cycles.It involves conducting wetting-drying cycles using sodiu...This study investigates the impact of bedding plane orientation on sodium chloride(NaCl)precipitation in a calcarenite stone,subjected to salt weathering cycles.It involves conducting wetting-drying cycles using sodium chloride on two series of specimens sampled parallel and perpendicular to the bedding plane.Capillary imbibition was carried out using saline solutions of two concentrations(15 g/L and 45 g/L).SEM observations show that,across all contaminated samples,halite precipitates mainly on the surface,in the form of efflorescence,while subflorescence remains negligible.The analysis identifies two distinct halite morphologies:(i)cubic crystals of 2 to 10μm at grain boundaries and(ii)xenomorphic aggregates on pore walls,reflecting that the size and morphology of halite crystals vary according to local nucleation conditions,influenced by the mineralogical composition of the substrates and the degree of supersaturation reached during the cycles.X-ray diffraction analysis revealed significantly higher halite precipitation in samples oriented perpendicular to the sediment bedding(4.53–5.22%)than in those oriented parallel(2.71–4.17%),indicating that bedding plane orientation is a determining factor in weathering processes and the evolution of petrophysical properties.These results demonstrate that capillary transport is intrinsically anisotropic in calcarenite,with bedding orientation controlling both the amount of precipitated salt and the location of crystallizations.This study thus establishes a solid mechanistic framework for predicting salt weathering patterns in stratified heritage stones,and offers concrete perspectives for optimizing conservation strategies in coastal environments.展开更多
The present work is devoted to the determination of linear effective thermal conductivity of porous rocks characterized by an assemblage of grains(oolites) coated by a matrix. Two distinct classes of pores, i.e.microp...The present work is devoted to the determination of linear effective thermal conductivity of porous rocks characterized by an assemblage of grains(oolites) coated by a matrix. Two distinct classes of pores, i.e.micropores or intra oolitic pores(oolite porosity) and mesopores or inter oolitic pores(inter oolite porosity), are taken into account. The overall porosity is supposed to be connected and decomposed into oolite porosity and matrix porosity. Within the framework of Hashin composite sphere assemblage(CSA)models, a two-step homogenization method is developed. At the first homogenization step, pores are assembled into two layers by using self-consistent scheme(SCS). At the second step, the two porous layers constituting the oolites and the matrix are assembled by using generalized self-consistent scheme(GSCS) and referred to as three-phase model. Numerical results are presented for data representative of a porous oolitic limestone. It is shown that the influence of porosity on the overall thermal conductivity of such materials may be significant.展开更多
Natural materials(e.g. rocks and soils) are porous media, whose microstructures present a wide diversity.They generally consist of a heterogeneous solid phase and a porous phase which may be fully or partially saturat...Natural materials(e.g. rocks and soils) are porous media, whose microstructures present a wide diversity.They generally consist of a heterogeneous solid phase and a porous phase which may be fully or partially saturated with one or more fluids. The prediction of elastic and acoustic properties of porous materials is very important in many fields, such as physics of rocks, reservoir geophysics, civil engineering, construction field and study of the behavior of historical monuments. The aim of this work is to predict the elastic and acoustic behaviors of isotropic porous materials of a solid matrix containing dry, saturated and partially saturated spherical pores. For this, a homogenization technique based on the Morie Tanaka model is presented to connect the elastic and acoustic properties to porosity and degree of water saturation. Non-destructive ultrasonic technique is used to determine the elastic properties from measurements of P-wave velocities. The results obtained show the influence of porosity and degree of water saturation on the effective properties. The various predictions of Morie Tanaka model are then compared with experimental results for the elastic and acoustic properties of calcarenite.展开更多
Climate change is a major concern of humanity. One of the consequences of climate change is global warming causing melting glaciers, rising sea levels and shoreline regression. In Togo, the regression of shoreline lea...Climate change is a major concern of humanity. One of the consequences of climate change is global warming causing melting glaciers, rising sea levels and shoreline regression. In Togo, the regression of shoreline leads to coastal erosion with significant damage on socio-economic infrastructures and hu</span><span style="font-family:Verdana;">man habitats. This research, basing on geospatial techniques, focuses on coastal </span><span style="font-family:Verdana;">erosion monitoring from 1988 to 2018 in Togo. It is interested in the extrac</span><span style="font-family:Verdana;">tion of shoreline and in the analysis of change. Various satellite images index</span></span><span style="font-family:Verdana;">es</span><span style="font-family:""> </span><span style="font-family:""><span style="font-family:Verdana;">have been developed for shoreline extraction but the major scientific problem concerns the precision of the different classification algorithms methods used for the extraction of the shoreline from these water index. This study used NDWI index from multisource satellite images. It assesses the performance of </span><span style="font-family:Verdana;">Otsu threshold segmentation, Iso Cluster Unsupervised Classification and Supp</span><span style="font-family:Verdana;">ort Vector Machine (SVM) Supervised Classification methods for the</span><span style="font-family:Verdana;"> extraction of the shoreline on NDWI index. The topographic morphology such </span><span style="font-family:Verdana;">as linear and non-linear coastal surfaces have been considered. The estimation</span><span style="font-family:Verdana;"> of the rates of change of the shoreline was performed using the statistical linear regression method (LRR). The results revealed that the SVM Supervised </span><span style="font-family:Verdana;">Classification method showed good performance on linear and non-linear coastal </span><span style="font-family:Verdana;">surface than the other methods. For the kinematics of the shoreline, the southwest of the Togolese coast has an average erosion rate ranging from 2.49 to 5.07 m per year. The results obtained will serve as decision-making support tools for the design and implementation of appropriate adaptations plans to avoid the immersion of the asphalt road by sea, displacement of population</span><b> </b><span style="font-family:Verdana;">and disturbance of human habitats.展开更多
It is essential to study the porosity,thermal conductivity,and P-wave velocity of calcarenites,as well as the anisotropy coefficients of the thermal conductivity and P-wave velocity,for civil engineering,and conservat...It is essential to study the porosity,thermal conductivity,and P-wave velocity of calcarenites,as well as the anisotropy coefficients of the thermal conductivity and P-wave velocity,for civil engineering,and conservation and restoration of historical monuments.This study focuses on measuring the thermal conductivity using the thermal conductivity scanning(TCS)technique and measuring the P-wave ve-locity using portable equipment.This was applied for some dry and saturated calcarenite samples in the horizontal and vertical directions(parallel and perpendicular to the bedding plane,respectively).The calcarenites were selected from some historical monuments in Morocco.These physical properties were measured in the laboratory to find a reliable relationship between all of these properties.As a result of the statistical analysis of the obtained data,excellent linear relationships were observed between the porosity and both the thermal conductivity and porosity.These relationships are characterized by relatively high coefficients of determination for the horizontal and vertical samples.Based on the thermal conductivity and P-wave velocity values in these two directions,the anisotropy coefficients of these two properties were calculated.The internal structure and the pore fabric of the calcarenite samples were delineated using scanning electron microscopy(SEM),while their chemical and mineral compositions were studied using the energy dispersive X-ray analysis(EDXA)and X-ray diffraction(XRD)techniques.展开更多
For decades, Africa has undergone many crisis, affecting economy, climate, food, politics as well as society with irreparable consequences on the environment. The protection of the latter, being one of the cornerstone...For decades, Africa has undergone many crisis, affecting economy, climate, food, politics as well as society with irreparable consequences on the environment. The protection of the latter, being one of the cornerstones of sustainable development, is only possible if it＇s based on a reliable and rigorous diagnosis and inventory. This study suggests a method to characterize natural resources, in particular agricultural ones, by showing their landscape context. In this perspective and in the absence of any pre-existing mapping, as it is often the case in Africa, this work provides a simple and reproducible approach that merely uses Landsat Thematic Mapper （TM） （free） images, with the only constraint of the cross-checking of several images at different times of the plant cycle.展开更多
Updating an authoritative Land Use and Land Cover(LULC)database requires many resources.Volunteered geographic information(VGI)involves citizens in the collection of data about their spatial environment.There is a gro...Updating an authoritative Land Use and Land Cover(LULC)database requires many resources.Volunteered geographic information(VGI)involves citizens in the collection of data about their spatial environment.There is a growing interest in using existing VGI to update authoritative databases.This paper presents a framework aimed at integrating multi-source VGI based on a data fusion technique,in order to update an authoritative land use database.Each VGI data source is considered to be an independent source of information,which is fused together using Dempster-Shafer Theory(DST).The framework is tested in the updating of the authoritative land use data produced by the French National Mapping Agency.Four data sets were collected from several in-situ and remote campaigns run between 2018 and 2020 by contributors with varying profiles.The data fusion approach achieved an overall accuracy of 85.6%for the 144 features having at least two contributions when the confidence threshold was set to 0.05.Despite the heterogeneity and limited amount of VGI used,the results are promising,with 99%of the LU polygons updated or enriched.These results show the potential of using multi-source VGI to update or enrich authoritative LU data and potentially LULC data more generally。展开更多
基金funded by the European Union's Horizon 2020 research and innovation programme under a grant agreement (Grant No.847593)partially supported by the Fundamental Research Funds for the Central Universities (Grant No.22120240029).
文摘This study presents a fully coupled thermo-hydro-mechanical (THM) constitutive model for clay rocks. The model is formulated within the elastic-viscoplasticity framework, which considers nonlinearity and softening after peak strength, anisotropy of stiffness and strength, as well as permeability variation due to damage. In addition, the mechanical properties are coupled with thermal phenomena and accumulated plastic strains. The adopted nonlocal and viscoplastic approaches enhance numerical efficiency and provide the possibility to simulate localization phenomena. The model is validated against experimental data from laboratory tests conducted on Callovo-Oxfordian (COx) claystone samples that are initially unsaturated and under suction. The tests include a thermal phase where the COx specimens are subjected to different temperature increases. A good agreement with experimental data is obtained. In addition, parametric analyses are carried out to investigate the influence of the hydraulic boundary conditions (B.C.) and post-failure behavior models on the THM behavior evolution. It is shown that different drainage conditions affect the thermally induced pore pressures that, in turn, influence the onset of softening. The constitutive model presented constitutes a promising approach for simulating the most important features of the THM behavior of clay rocks. It is a tool with a high potential for application to several relevant case studies, such as thermal fracturing analysis of nuclear waste disposal systems.
文摘This study investigates the impact of bedding plane orientation on sodium chloride(NaCl)precipitation in a calcarenite stone,subjected to salt weathering cycles.It involves conducting wetting-drying cycles using sodium chloride on two series of specimens sampled parallel and perpendicular to the bedding plane.Capillary imbibition was carried out using saline solutions of two concentrations(15 g/L and 45 g/L).SEM observations show that,across all contaminated samples,halite precipitates mainly on the surface,in the form of efflorescence,while subflorescence remains negligible.The analysis identifies two distinct halite morphologies:(i)cubic crystals of 2 to 10μm at grain boundaries and(ii)xenomorphic aggregates on pore walls,reflecting that the size and morphology of halite crystals vary according to local nucleation conditions,influenced by the mineralogical composition of the substrates and the degree of supersaturation reached during the cycles.X-ray diffraction analysis revealed significantly higher halite precipitation in samples oriented perpendicular to the sediment bedding(4.53–5.22%)than in those oriented parallel(2.71–4.17%),indicating that bedding plane orientation is a determining factor in weathering processes and the evolution of petrophysical properties.These results demonstrate that capillary transport is intrinsically anisotropic in calcarenite,with bedding orientation controlling both the amount of precipitated salt and the location of crystallizations.This study thus establishes a solid mechanistic framework for predicting salt weathering patterns in stratified heritage stones,and offers concrete perspectives for optimizing conservation strategies in coastal environments.
基金support from TAMER (Trans-Atlantic Micromechanics Evolving Research) European Project (materials containing inhomogeneities of diverse physical properties, shapes and orientations)FP7 Project TAMER IRSES-GA2013-610547
文摘The present work is devoted to the determination of linear effective thermal conductivity of porous rocks characterized by an assemblage of grains(oolites) coated by a matrix. Two distinct classes of pores, i.e.micropores or intra oolitic pores(oolite porosity) and mesopores or inter oolitic pores(inter oolite porosity), are taken into account. The overall porosity is supposed to be connected and decomposed into oolite porosity and matrix porosity. Within the framework of Hashin composite sphere assemblage(CSA)models, a two-step homogenization method is developed. At the first homogenization step, pores are assembled into two layers by using self-consistent scheme(SCS). At the second step, the two porous layers constituting the oolites and the matrix are assembled by using generalized self-consistent scheme(GSCS) and referred to as three-phase model. Numerical results are presented for data representative of a porous oolitic limestone. It is shown that the influence of porosity on the overall thermal conductivity of such materials may be significant.
文摘Natural materials(e.g. rocks and soils) are porous media, whose microstructures present a wide diversity.They generally consist of a heterogeneous solid phase and a porous phase which may be fully or partially saturated with one or more fluids. The prediction of elastic and acoustic properties of porous materials is very important in many fields, such as physics of rocks, reservoir geophysics, civil engineering, construction field and study of the behavior of historical monuments. The aim of this work is to predict the elastic and acoustic behaviors of isotropic porous materials of a solid matrix containing dry, saturated and partially saturated spherical pores. For this, a homogenization technique based on the Morie Tanaka model is presented to connect the elastic and acoustic properties to porosity and degree of water saturation. Non-destructive ultrasonic technique is used to determine the elastic properties from measurements of P-wave velocities. The results obtained show the influence of porosity and degree of water saturation on the effective properties. The various predictions of Morie Tanaka model are then compared with experimental results for the elastic and acoustic properties of calcarenite.
文摘Climate change is a major concern of humanity. One of the consequences of climate change is global warming causing melting glaciers, rising sea levels and shoreline regression. In Togo, the regression of shoreline leads to coastal erosion with significant damage on socio-economic infrastructures and hu</span><span style="font-family:Verdana;">man habitats. This research, basing on geospatial techniques, focuses on coastal </span><span style="font-family:Verdana;">erosion monitoring from 1988 to 2018 in Togo. It is interested in the extrac</span><span style="font-family:Verdana;">tion of shoreline and in the analysis of change. Various satellite images index</span></span><span style="font-family:Verdana;">es</span><span style="font-family:""> </span><span style="font-family:""><span style="font-family:Verdana;">have been developed for shoreline extraction but the major scientific problem concerns the precision of the different classification algorithms methods used for the extraction of the shoreline from these water index. This study used NDWI index from multisource satellite images. It assesses the performance of </span><span style="font-family:Verdana;">Otsu threshold segmentation, Iso Cluster Unsupervised Classification and Supp</span><span style="font-family:Verdana;">ort Vector Machine (SVM) Supervised Classification methods for the</span><span style="font-family:Verdana;"> extraction of the shoreline on NDWI index. The topographic morphology such </span><span style="font-family:Verdana;">as linear and non-linear coastal surfaces have been considered. The estimation</span><span style="font-family:Verdana;"> of the rates of change of the shoreline was performed using the statistical linear regression method (LRR). The results revealed that the SVM Supervised </span><span style="font-family:Verdana;">Classification method showed good performance on linear and non-linear coastal </span><span style="font-family:Verdana;">surface than the other methods. For the kinematics of the shoreline, the southwest of the Togolese coast has an average erosion rate ranging from 2.49 to 5.07 m per year. The results obtained will serve as decision-making support tools for the design and implementation of appropriate adaptations plans to avoid the immersion of the asphalt road by sea, displacement of population</span><b> </b><span style="font-family:Verdana;">and disturbance of human habitats.
文摘It is essential to study the porosity,thermal conductivity,and P-wave velocity of calcarenites,as well as the anisotropy coefficients of the thermal conductivity and P-wave velocity,for civil engineering,and conservation and restoration of historical monuments.This study focuses on measuring the thermal conductivity using the thermal conductivity scanning(TCS)technique and measuring the P-wave ve-locity using portable equipment.This was applied for some dry and saturated calcarenite samples in the horizontal and vertical directions(parallel and perpendicular to the bedding plane,respectively).The calcarenites were selected from some historical monuments in Morocco.These physical properties were measured in the laboratory to find a reliable relationship between all of these properties.As a result of the statistical analysis of the obtained data,excellent linear relationships were observed between the porosity and both the thermal conductivity and porosity.These relationships are characterized by relatively high coefficients of determination for the horizontal and vertical samples.Based on the thermal conductivity and P-wave velocity values in these two directions,the anisotropy coefficients of these two properties were calculated.The internal structure and the pore fabric of the calcarenite samples were delineated using scanning electron microscopy(SEM),while their chemical and mineral compositions were studied using the energy dispersive X-ray analysis(EDXA)and X-ray diffraction(XRD)techniques.
文摘For decades, Africa has undergone many crisis, affecting economy, climate, food, politics as well as society with irreparable consequences on the environment. The protection of the latter, being one of the cornerstones of sustainable development, is only possible if it＇s based on a reliable and rigorous diagnosis and inventory. This study suggests a method to characterize natural resources, in particular agricultural ones, by showing their landscape context. In this perspective and in the absence of any pre-existing mapping, as it is often the case in Africa, this work provides a simple and reproducible approach that merely uses Landsat Thematic Mapper （TM） （free） images, with the only constraint of the cross-checking of several images at different times of the plant cycle.
基金supported by Horizon 2020 Framework Programme[grant number 689812].
文摘Updating an authoritative Land Use and Land Cover(LULC)database requires many resources.Volunteered geographic information(VGI)involves citizens in the collection of data about their spatial environment.There is a growing interest in using existing VGI to update authoritative databases.This paper presents a framework aimed at integrating multi-source VGI based on a data fusion technique,in order to update an authoritative land use database.Each VGI data source is considered to be an independent source of information,which is fused together using Dempster-Shafer Theory(DST).The framework is tested in the updating of the authoritative land use data produced by the French National Mapping Agency.Four data sets were collected from several in-situ and remote campaigns run between 2018 and 2020 by contributors with varying profiles.The data fusion approach achieved an overall accuracy of 85.6%for the 144 features having at least two contributions when the confidence threshold was set to 0.05.Despite the heterogeneity and limited amount of VGI used,the results are promising,with 99%of the LU polygons updated or enriched.These results show the potential of using multi-source VGI to update or enrich authoritative LU data and potentially LULC data more generally。
