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Yu-jun Cui - One of the best experts on this subject based on the ideXlab platform.
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Impact of excavation damage on the thermo-hydro-mechanical properties of natural Boom Clay
Engineering Geology, 2015Co-Authors: Linh Quyen Dao, Yu-jun Cui, Anh Minh Tang, Jean-michel Pereira, Xavier SillenAbstract:Boom Clay has been considered as a potential host-rock for the geological radioactive waste disposal in Belgium. In this context, it is important to well understand the thermo-hydro-mechanical behaviour of this Clay around the disposal galleries. In this study, the effect of excavation damage on the thermo-hydro-mechanical properties of natural Boom Clay around the Connecting gallery (excavated in 2002) in the Mol underground Research Laboratory HADES (High-Activity Disposal Experimental Site) was investigated. Several samples taken from a horizontal borehole drilled in July 2012 were tested. The thermal conductivity in three different orientations (perpendicular, parallel, and 45° to the bedding plane) was measured using the needle probe method. The results show a cross-anisotropy of natural Boom Clay and an impact of the excavation damage on the thermal property of samples near the gallery. To further investigate the anisotropy behaviour, bender element tests were carried out under unconfined conditions to determine the small-strain shear modulus also in three different orientations. The obtained results confirm the anisotropic behaviour of Boom Clay. Moreover, the evolution of small-strain shear modulus with the distance from the gallery axis (r) was found to be similar to that of thermal conductivity: the values in the zone near the gallery are lower than those in the far field. From these experimental data, an extent of the excavation damaged zone (EDZ) of 4 m from the connecting gallery axis was determined. Further investigations on the microstructure of several samples taken at different distances r by mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) methods were carried out. Macro-pores of diameter ≥5 μm were identified in the samples near the gallery. The identified macro-pores were related to the effect of excavation damage, and a damage variable was thus defined, allowing a damage model to be developed. The values of the two model parameters have been determined from the observed relationship between macro-porosity and thermal conductivity. Comparisons between the predicted and experimental results in terms of small strain shear modulus and hydraulic conductivity show a reasonable agreement.
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Investigating the anisotropy of the shear modulus of natural Boom Clay
Géotechnique Letters, 2014Co-Authors: Linh Quyen Dao, Yu-jun Cui, Anh Minh Tang, Jean-michel Pereira, Xavier SillenAbstract:Boom Clay is considered to be a potential host formation for a geological repository of radioactive waste in Belgium. In this context, a thorough understanding of its mechanical behaviour is thus important. In this study, the anisotropy of the shear modulus of natural Boom Clay samples was investigated using the bender element method. Seven samples located at different distances from the connecting gallery of the HADES underground research laboratory were tested for shearing in three different directions with respect to the bedding plane. The results obtained confirm the mechanical anisotropy of Boom Clay. Furthermore, the values of small-strain shear modulus in the near field of the gallery were found to be lower than those in the far field, suggesting that the mechanical properties of Boom Clay remain affected by gallery excavation damage that occurred more than 10 years ago.
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Anisotropic thermal conductivity of natural Boom Clay
Applied Clay Science, 2014Co-Authors: Linh Quyen Dao, Pierre Delage, Anh Minh Tang, Yu-jun Cui, Jean-michel Pereira, Xavier SillenAbstract:The thermal conductivity of host rocks is an important parameter in the design of deep geological disposal of heat-emitting radioactive waste. Due to bedding, heat transfer in sedimentary rocks is affected by their transversally isotropic structure. In this work, an experimental program is run to measure the thermal conductivities of Boom Clay along various orientations with respect to the bedding plane by using the needle thermal probe technique. Measurements were performed on specimens obtained from cores drilled from the HADES Underground Research Laboratory (URL) at Mol, Belgium, at a depth of 223 m. The thermal conductivity values obtained are in good agreement with those previously published, confirming the thermal anisotropy of Boom Clay. Moreover, the observed changes in thermal conductivity with respect to the distance to the gallery provide further evidence on the extent of the Excavation Damaged Zone around the gallery.
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On The Thermal Consolidation Of Boom Clay
arXiv: Geophysics, 2012Co-Authors: Pierre Delage, Nabil Sultan, Yu-jun CuiAbstract:When a mass of saturated Clay is heated, as in the case of host soils surrounding nuclear waste disposals at great depth, the thermal expansion of the constituents generates excess pore pressures. The mass of Clay is submitted to gradients of pore pressure and temperature, to hydraulic and thermal flows, and to changes in its mechanical properties. In this work, some of these aspects were experimentally studied in the case of Boom Clay, so as to help predicting the response of the soil, in relation with investigations made in the Belgian underground laboratory at Mol. Results of slow heating tests with careful volume change measurements showed that a reasonable prediction of the thermal expansion of the Clay-water system was obtained by using the thermal properties of free water. In spite of the density of Boom Clay, no significant effect of water adsorption was observed. The thermal consolidation of Boom Clay was studied through fast heating tests. A simple analysis shows that the hydraulic and thermal transfers are uncoupled. Experimental results from fast heating tests showed that the consolidation coefficient does not change significantly with increased temperature, due to the opposite effect of increasing permeability and decreasing porosity. The changes of permeability with temperature were investigated by running constant head measurements at various temperatures. An indirect analysis, based on the estimation of the mv consolidation parameter, showed that the indirect method of estimating the permeability from consolidation tests should be considered carefully. Intrinsic permeability values were derived by considering the change of the viscosity of free water with temperature. A unique relationship between the intrinsic permeability and the porosity was observed, with no dependence on temperature, confirming that the flow involved in the permeability test only concerns free water.
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An experimental study on the secondary deformation of Boom Clay
Applied Clay Science, 2012Co-Authors: Yongfeng Deng, Anh Minh Tang, Yu-jun Cui, X. SillenAbstract:Abstract Boom Clay formation, a deposit of slightly over-consolidated marine Clay that belongs to the Oligocene series in the north east of Belgium, has been studied as a possible host material of nuclear waste disposal. In this context, the long-term deformation behavior of Boom Clay is of crucial importance in the performance assessment of the whole storage system. In this study, low and high pressure oedometer tests are carried out; the e-log σ′ v (void ratio–logarithm of vertical effective stress) and e-log t (void ratio–logarithm of time) curves obtained are used to determine the compression index C c *, swelling index C s * and secondary deformation coefficient C α during both loading and unloading. The relationship between C α and the effective stress ratio (σ′ v /σ′ c , vertical effective stress to pre-consolidation stress) is analyzed, and it is observed that C α increases linearly with log σ′ v /σ′ c . Examination of the ratio of C α / C c * for various soils shows that the secondary deformation behavior of Boom Clay is similar to that of shale and mudstone. The relation between C α and C c * is linear; but the relation between C α and C s * is bi-linear. The bi-linearity observed is related to two different mechanisms: the mechanically dominated rebounding and the physico-chemically dominated swelling.
X. Sillen - One of the best experts on this subject based on the ideXlab platform.
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Effects of temperature and thermally-induced microstructure change on hydraulic conductivity of Boom Clay
Journal of Rock Mechanics and Geotechnical Engineering, 2017Co-Authors: Weizhong Chen, Yu Hongdan, X. SillenAbstract:Abstract Boom Clay is one of the potential host rocks for deep geological disposal of high-level radioactive nuclear waste in Belgium. In order to investigate the mechanism of hydraulic conductivity variation under complex thermo-mechanical coupling conditions and to better understand the thermo-hydro-mechanical (THM) coupling behaviour of Boom Clay, a series of permeability tests using temperature-controlled triaxial cell has been carried out on the Boom Clay samples taken from Belgian underground research laboratory (URL) HADES. Due to its sedimentary nature, Boom Clay presents across-anisotropy with respect to its sub-horizontal bedding plane. Direct measurements of the vertical (Kv) and horizontal (Kh) hydraulic conductivities show that the hydraulic conductivity at 80 °C is about 2.4 times larger than that at room temperature (23 °C), and the hydraulic conductivity variation with temperature is basically reversible during heating–cooling cycle. The anisotropic property of Boom Clay is studied by scanning electron microscope (SEM) tests, which highlight the transversely isotropic characteristics of intact Boom Clay. It is shown that the sub-horizontal bedding feature accounts for the horizontal permeability higher than the vertical one. The measured increment in hydraulic conductivity with temperature is lower than the calculated one when merely considering the changes in water kinematic viscosity and density with temperature. The nuclear magnetic resonance (NMR) tests have also been carried out to investigate the impact of microstructure variation on the THM properties of Clay. The results show that heating under unconstrained boundary condition will produce larger size of pores and weaken the microstructure. The discrepancy between the hydraulic conductivity experimentally measured and predicted (considering water viscosity and density changes with temperature) can be attributed to the microstructural weakening effect on the thermal volume change behaviour of Boom Clay. Based on the experimental results, a hydraulic conductivity evolution model is proposed and then implemented in ABAQUS. Three-dimensional (3D) numerical simulation of the admissible thermal loading for argillaceous storage (ATLAS) III in situ heating test has been conducted subsequently, and the numerical results are in good agreement with field measurements.
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Creep behavior of Boom Clay
International Journal of Rock Mechanics and Mining Sciences, 2015Co-Authors: Yu Hongdan, Weizhong Chen, Zhe Gong, Xianjun Tan, Ma Yongshang, X. SillenAbstract:Abstract Several creep tests (lasting more than one year) were performed to study the delayed mechanical behavior of Boom Clay under the hydro-mechanical coupling effect. To prevent the soil from swelling as much as possible during re-saturation, the samples were submitted to a confining pressure close to the in situ effective mean stress (2.5 MPa) at a room temperature of 21 °C. However, certain swelling still exists at the beginning of the saturation. Creep tests further highlight the creep potential of Boom Clay. Delayed behavior became more and more significant as the deviatoric stress increased. A deviatoric stress threshold (approximately 1.0 MPa), below which only primary creep occurred, was proved to exist from the development of secondary and tertiary creep phases during the creep tests. If we introduce a quasi-steady state creep rate, i.e., the average creep rate after the creep deformation becoming stable, it can be found that the quasi-steady state creep rate of Boom Clay is on the order of 10−6 e/h under low deviatoric stress (1.5 MPa) in the laboratory, which is on the same order as the average creep rate of the in situ measurements in the second year (1988). However, in situ measurements show that steady creep state of the host rock was not reached even after five years. The in situ quasi-steady state diameter reduction rate calculated from the average of 10 years (1996–2006) of stable deformation of the tunnel linings is on the order of 10−8 e/h.
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Thermal Impact on Damaged Boom Clay and Opalinus Clay: Permeameter and Isostatic Tests with μCT Scanning
Rock Mechanics and Rock Engineering, 2014Co-Authors: G J Chen, X. Sillen, M Honty, T. Maes, F. Vandervoort, P. Van Marcke, M. Dierick, P. VanderniepenAbstract:Within the framework of the TIMODAZ project, permeameter tests and isostatic tests were performed on Boom Clay and Opalinus Clay in order to assess the impact of temperature, pore water composition, and confining stress on the sealing of damaged samples of Boom Clay and Opalinus Clay. A microfocus X-ray computed tomography technique was used to visualize the evolution of the sealing process. Compared to the fast sealing of Boom Clay, the sealing of Opalinus Clay was much slower. The heating showed a significant, favorable impact on the sealing behavior of Opalinus Clay under permeameter test conditions, while the sealing behavior of Boom Clay appeared to be unaffected. Tests performed under isostatic conditions did not reveal a significant influence of a heating–cooling cycle on the sealing behavior of these Clays. The reappearance of the fractures or holes in the samples after dismantling confirms earlier observations which showed that after sealing, the original mechanical properties are not recovered. In other words, a heating cycle does not seem to induce healing.
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A Transversely Isotropic Damage Model for Boom Clay
Rock Mechanics and Rock Engineering, 2013Co-Authors: Yu Hongdan, Weizhong Chen, X. SillenAbstract:Boom Clay can be considered as a transversely isotropic geomaterial. However, due to lack of experimental evidence and data base, it is still difficult to describe the transversely isotropic plastic behavior of this argillaceous rock. In this paper, we present first, by means of an experimental approach, the main features of the mechanical properties of Boom Clay. Then, combining the transversely isotropic elastic model and the modified Mohr–Coulomb criterion, a suitable constitutive model is introduced so as to fully describe the mechanical behavior of the studied material, in which, an elastic damage law which takes into consideration, the transversely isotropic effect, a plastic hardening law and a plastic damage law were introduced to describe the nonlinear elastic, hardening and softening behavior of Boom Clay. As a preliminary step, the evolution law of both elastic moduli and Poisson’s ratio during the elastic stage was obtained by direct analysis of the test data. The synchronism of the elastic damage in both transversal and axial directions was proved by this method. Some of the parameters of the model in the elastic stage were also determined by direct analysis method and further verified by back analysis. Other unknown parameters in the model were determined by back analysis.
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An experimental study on the secondary deformation of Boom Clay
Applied Clay Science, 2012Co-Authors: Yongfeng Deng, Anh Minh Tang, Yu-jun Cui, X. SillenAbstract:Abstract Boom Clay formation, a deposit of slightly over-consolidated marine Clay that belongs to the Oligocene series in the north east of Belgium, has been studied as a possible host material of nuclear waste disposal. In this context, the long-term deformation behavior of Boom Clay is of crucial importance in the performance assessment of the whole storage system. In this study, low and high pressure oedometer tests are carried out; the e-log σ′ v (void ratio–logarithm of vertical effective stress) and e-log t (void ratio–logarithm of time) curves obtained are used to determine the compression index C c *, swelling index C s * and secondary deformation coefficient C α during both loading and unloading. The relationship between C α and the effective stress ratio (σ′ v /σ′ c , vertical effective stress to pre-consolidation stress) is analyzed, and it is observed that C α increases linearly with log σ′ v /σ′ c . Examination of the ratio of C α / C c * for various soils shows that the secondary deformation behavior of Boom Clay is similar to that of shale and mudstone. The relation between C α and C c * is linear; but the relation between C α and C s * is bi-linear. The bi-linearity observed is related to two different mechanisms: the mechanically dominated rebounding and the physico-chemically dominated swelling.
Anh Minh Tang - One of the best experts on this subject based on the ideXlab platform.
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Impact of excavation damage on the thermo-hydro-mechanical properties of natural Boom Clay
Engineering Geology, 2015Co-Authors: Linh Quyen Dao, Yu-jun Cui, Anh Minh Tang, Jean-michel Pereira, Xavier SillenAbstract:Boom Clay has been considered as a potential host-rock for the geological radioactive waste disposal in Belgium. In this context, it is important to well understand the thermo-hydro-mechanical behaviour of this Clay around the disposal galleries. In this study, the effect of excavation damage on the thermo-hydro-mechanical properties of natural Boom Clay around the Connecting gallery (excavated in 2002) in the Mol underground Research Laboratory HADES (High-Activity Disposal Experimental Site) was investigated. Several samples taken from a horizontal borehole drilled in July 2012 were tested. The thermal conductivity in three different orientations (perpendicular, parallel, and 45° to the bedding plane) was measured using the needle probe method. The results show a cross-anisotropy of natural Boom Clay and an impact of the excavation damage on the thermal property of samples near the gallery. To further investigate the anisotropy behaviour, bender element tests were carried out under unconfined conditions to determine the small-strain shear modulus also in three different orientations. The obtained results confirm the anisotropic behaviour of Boom Clay. Moreover, the evolution of small-strain shear modulus with the distance from the gallery axis (r) was found to be similar to that of thermal conductivity: the values in the zone near the gallery are lower than those in the far field. From these experimental data, an extent of the excavation damaged zone (EDZ) of 4 m from the connecting gallery axis was determined. Further investigations on the microstructure of several samples taken at different distances r by mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) methods were carried out. Macro-pores of diameter ≥5 μm were identified in the samples near the gallery. The identified macro-pores were related to the effect of excavation damage, and a damage variable was thus defined, allowing a damage model to be developed. The values of the two model parameters have been determined from the observed relationship between macro-porosity and thermal conductivity. Comparisons between the predicted and experimental results in terms of small strain shear modulus and hydraulic conductivity show a reasonable agreement.
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anisotropy in oedometer test on natural Boom Clay
2015Co-Authors: Anh Minh Tang, Pierre Delage, Xiangling Li, Xavier SillenAbstract:The mechanical behaviour of Boom Clay has been studied for many years in the context of geological disposal of radioactive waste in Belgium. The aim of this study is to investigate the anisotropic behaviour of Boom Clay in terms of compressibility and hydraulic conductivity. Oedometer tests (with effective vertical stress (\( \sigma_{v}^{{\prime }} \)) up to 32 MPa) were carried out on samples of various orientations: parallel, perpendicular and inclined 45° to the bedding plane. The compressibility index (C c ) and swelling index (C s ) were compared. Only a slight difference between these parameters was observed, suggesting that the anisotropic behaviour of Boom Clay cannot be revealed under the test conditions adopted. The hydraulic conductivity (k) was also determined by the Casagrande’s method for different values of vertical effective stress (\( \sigma_{v}^{{\prime }} \)). Unlike compressibility, the hydraulic conductivity, however, showed a clear anisotropic behaviour with k ver < k inc < k hor .
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Investigating the anisotropy of the shear modulus of natural Boom Clay
Géotechnique Letters, 2014Co-Authors: Linh Quyen Dao, Yu-jun Cui, Anh Minh Tang, Jean-michel Pereira, Xavier SillenAbstract:Boom Clay is considered to be a potential host formation for a geological repository of radioactive waste in Belgium. In this context, a thorough understanding of its mechanical behaviour is thus important. In this study, the anisotropy of the shear modulus of natural Boom Clay samples was investigated using the bender element method. Seven samples located at different distances from the connecting gallery of the HADES underground research laboratory were tested for shearing in three different directions with respect to the bedding plane. The results obtained confirm the mechanical anisotropy of Boom Clay. Furthermore, the values of small-strain shear modulus in the near field of the gallery were found to be lower than those in the far field, suggesting that the mechanical properties of Boom Clay remain affected by gallery excavation damage that occurred more than 10 years ago.
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Anisotropic thermal conductivity of natural Boom Clay
Applied Clay Science, 2014Co-Authors: Linh Quyen Dao, Pierre Delage, Anh Minh Tang, Yu-jun Cui, Jean-michel Pereira, Xavier SillenAbstract:The thermal conductivity of host rocks is an important parameter in the design of deep geological disposal of heat-emitting radioactive waste. Due to bedding, heat transfer in sedimentary rocks is affected by their transversally isotropic structure. In this work, an experimental program is run to measure the thermal conductivities of Boom Clay along various orientations with respect to the bedding plane by using the needle thermal probe technique. Measurements were performed on specimens obtained from cores drilled from the HADES Underground Research Laboratory (URL) at Mol, Belgium, at a depth of 223 m. The thermal conductivity values obtained are in good agreement with those previously published, confirming the thermal anisotropy of Boom Clay. Moreover, the observed changes in thermal conductivity with respect to the distance to the gallery provide further evidence on the extent of the Excavation Damaged Zone around the gallery.
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An experimental study on the secondary deformation of Boom Clay
Applied Clay Science, 2012Co-Authors: Yongfeng Deng, Anh Minh Tang, Yu-jun Cui, X. SillenAbstract:Abstract Boom Clay formation, a deposit of slightly over-consolidated marine Clay that belongs to the Oligocene series in the north east of Belgium, has been studied as a possible host material of nuclear waste disposal. In this context, the long-term deformation behavior of Boom Clay is of crucial importance in the performance assessment of the whole storage system. In this study, low and high pressure oedometer tests are carried out; the e-log σ′ v (void ratio–logarithm of vertical effective stress) and e-log t (void ratio–logarithm of time) curves obtained are used to determine the compression index C c *, swelling index C s * and secondary deformation coefficient C α during both loading and unloading. The relationship between C α and the effective stress ratio (σ′ v /σ′ c , vertical effective stress to pre-consolidation stress) is analyzed, and it is observed that C α increases linearly with log σ′ v /σ′ c . Examination of the ratio of C α / C c * for various soils shows that the secondary deformation behavior of Boom Clay is similar to that of shale and mudstone. The relation between C α and C c * is linear; but the relation between C α and C s * is bi-linear. The bi-linearity observed is related to two different mechanisms: the mechanically dominated rebounding and the physico-chemically dominated swelling.
Pierre Delage - One of the best experts on this subject based on the ideXlab platform.
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anisotropy in oedometer test on natural Boom Clay
2015Co-Authors: Anh Minh Tang, Pierre Delage, Xiangling Li, Xavier SillenAbstract:The mechanical behaviour of Boom Clay has been studied for many years in the context of geological disposal of radioactive waste in Belgium. The aim of this study is to investigate the anisotropic behaviour of Boom Clay in terms of compressibility and hydraulic conductivity. Oedometer tests (with effective vertical stress (\( \sigma_{v}^{{\prime }} \)) up to 32 MPa) were carried out on samples of various orientations: parallel, perpendicular and inclined 45° to the bedding plane. The compressibility index (C c ) and swelling index (C s ) were compared. Only a slight difference between these parameters was observed, suggesting that the anisotropic behaviour of Boom Clay cannot be revealed under the test conditions adopted. The hydraulic conductivity (k) was also determined by the Casagrande’s method for different values of vertical effective stress (\( \sigma_{v}^{{\prime }} \)). Unlike compressibility, the hydraulic conductivity, however, showed a clear anisotropic behaviour with k ver < k inc < k hor .
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Anisotropic thermal conductivity of natural Boom Clay
Applied Clay Science, 2014Co-Authors: Linh Quyen Dao, Pierre Delage, Anh Minh Tang, Yu-jun Cui, Jean-michel Pereira, Xavier SillenAbstract:The thermal conductivity of host rocks is an important parameter in the design of deep geological disposal of heat-emitting radioactive waste. Due to bedding, heat transfer in sedimentary rocks is affected by their transversally isotropic structure. In this work, an experimental program is run to measure the thermal conductivities of Boom Clay along various orientations with respect to the bedding plane by using the needle thermal probe technique. Measurements were performed on specimens obtained from cores drilled from the HADES Underground Research Laboratory (URL) at Mol, Belgium, at a depth of 223 m. The thermal conductivity values obtained are in good agreement with those previously published, confirming the thermal anisotropy of Boom Clay. Moreover, the observed changes in thermal conductivity with respect to the distance to the gallery provide further evidence on the extent of the Excavation Damaged Zone around the gallery.
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On The Thermal Consolidation Of Boom Clay
arXiv: Geophysics, 2012Co-Authors: Pierre Delage, Nabil Sultan, Yu-jun CuiAbstract:When a mass of saturated Clay is heated, as in the case of host soils surrounding nuclear waste disposals at great depth, the thermal expansion of the constituents generates excess pore pressures. The mass of Clay is submitted to gradients of pore pressure and temperature, to hydraulic and thermal flows, and to changes in its mechanical properties. In this work, some of these aspects were experimentally studied in the case of Boom Clay, so as to help predicting the response of the soil, in relation with investigations made in the Belgian underground laboratory at Mol. Results of slow heating tests with careful volume change measurements showed that a reasonable prediction of the thermal expansion of the Clay-water system was obtained by using the thermal properties of free water. In spite of the density of Boom Clay, no significant effect of water adsorption was observed. The thermal consolidation of Boom Clay was studied through fast heating tests. A simple analysis shows that the hydraulic and thermal transfers are uncoupled. Experimental results from fast heating tests showed that the consolidation coefficient does not change significantly with increased temperature, due to the opposite effect of increasing permeability and decreasing porosity. The changes of permeability with temperature were investigated by running constant head measurements at various temperatures. An indirect analysis, based on the estimation of the mv consolidation parameter, showed that the indirect method of estimating the permeability from consolidation tests should be considered carefully. Intrinsic permeability values were derived by considering the change of the viscosity of free water with temperature. A unique relationship between the intrinsic permeability and the porosity was observed, with no dependence on temperature, confirming that the flow involved in the permeability test only concerns free water.
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On the THM behaviour of a sheared Boom Clay sample: Application to the behaviour and sealing properties of the EDZ
Engineering Geology, 2012Co-Authors: Monfared Mohammad, Pierre Delage, Jean Sulem, Mehrdokht MohajeraniAbstract:In this study the effect of the temperature increase on the hydro-mechanical properties of sheared Boom Clay samples is investigated. Two samples of Boom Clay are resaturated in a new hollow cylinder triaxial cell with a short drainage path and then sheared by performing an axisymmetric triaxial loading. The effect of the undrained heating under deviatoric stress is studied on the first sample. It is shown that undrained temperature increase leads to an increase of pore water pressure and consequently to a decrease of the effective mean stress which brings the sample to failure. For an initially sheared sample, the failure occurs along the existing shear band which behaves as a weakness plane in the sample. The responses of the local strain measurement transducers clearly show the sliding of rigid blocks when failure occurs in the sample. The effect of the presence of a shear band on the permeability of the other Boom Clay sample is investigated at ambient temperature andat 80 °C. It is shownthat the presence of a shear band does not affect significantly the permeability. These results confirm the good self sealing properties of Boom Clay at ambient and at high temperature.
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Permeability changes in Boom Clay with temperature
arXiv: Other Condensed Matter, 2011Co-Authors: Pierre Delage, Nabil Sultan, Yu-jun Cui, Li Xiang LingAbstract:In the framework of research into radioactive waste disposal, this paper presents some tests carried out to investigate the effects of temperature on the changes in permeability of Boom between 20 and 90 deg C. Constant head permeability tests were carried out in a high pressure isotropic compression tests at various temperature and isotropic stresses. The results show that the changes in permeability of Boom Clay with temperature are only due to the changes in viscosity of free water with temperaure. This demonstrates on the one hand that the water involved in transfer at various temperatures is free water and on the other hand that there is apparently only few changes in the status of adsorbed water with respect to temperature between 20 and 90 deg C.
Xavier Sillen - One of the best experts on this subject based on the ideXlab platform.
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anisotropy in oedometer test on natural Boom Clay
2015Co-Authors: Anh Minh Tang, Pierre Delage, Xiangling Li, Xavier SillenAbstract:The mechanical behaviour of Boom Clay has been studied for many years in the context of geological disposal of radioactive waste in Belgium. The aim of this study is to investigate the anisotropic behaviour of Boom Clay in terms of compressibility and hydraulic conductivity. Oedometer tests (with effective vertical stress (\( \sigma_{v}^{{\prime }} \)) up to 32 MPa) were carried out on samples of various orientations: parallel, perpendicular and inclined 45° to the bedding plane. The compressibility index (C c ) and swelling index (C s ) were compared. Only a slight difference between these parameters was observed, suggesting that the anisotropic behaviour of Boom Clay cannot be revealed under the test conditions adopted. The hydraulic conductivity (k) was also determined by the Casagrande’s method for different values of vertical effective stress (\( \sigma_{v}^{{\prime }} \)). Unlike compressibility, the hydraulic conductivity, however, showed a clear anisotropic behaviour with k ver < k inc < k hor .
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Impact of excavation damage on the thermo-hydro-mechanical properties of natural Boom Clay
Engineering Geology, 2015Co-Authors: Linh Quyen Dao, Yu-jun Cui, Anh Minh Tang, Jean-michel Pereira, Xavier SillenAbstract:Boom Clay has been considered as a potential host-rock for the geological radioactive waste disposal in Belgium. In this context, it is important to well understand the thermo-hydro-mechanical behaviour of this Clay around the disposal galleries. In this study, the effect of excavation damage on the thermo-hydro-mechanical properties of natural Boom Clay around the Connecting gallery (excavated in 2002) in the Mol underground Research Laboratory HADES (High-Activity Disposal Experimental Site) was investigated. Several samples taken from a horizontal borehole drilled in July 2012 were tested. The thermal conductivity in three different orientations (perpendicular, parallel, and 45° to the bedding plane) was measured using the needle probe method. The results show a cross-anisotropy of natural Boom Clay and an impact of the excavation damage on the thermal property of samples near the gallery. To further investigate the anisotropy behaviour, bender element tests were carried out under unconfined conditions to determine the small-strain shear modulus also in three different orientations. The obtained results confirm the anisotropic behaviour of Boom Clay. Moreover, the evolution of small-strain shear modulus with the distance from the gallery axis (r) was found to be similar to that of thermal conductivity: the values in the zone near the gallery are lower than those in the far field. From these experimental data, an extent of the excavation damaged zone (EDZ) of 4 m from the connecting gallery axis was determined. Further investigations on the microstructure of several samples taken at different distances r by mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) methods were carried out. Macro-pores of diameter ≥5 μm were identified in the samples near the gallery. The identified macro-pores were related to the effect of excavation damage, and a damage variable was thus defined, allowing a damage model to be developed. The values of the two model parameters have been determined from the observed relationship between macro-porosity and thermal conductivity. Comparisons between the predicted and experimental results in terms of small strain shear modulus and hydraulic conductivity show a reasonable agreement.
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Investigating the anisotropy of the shear modulus of natural Boom Clay
Géotechnique Letters, 2014Co-Authors: Linh Quyen Dao, Yu-jun Cui, Anh Minh Tang, Jean-michel Pereira, Xavier SillenAbstract:Boom Clay is considered to be a potential host formation for a geological repository of radioactive waste in Belgium. In this context, a thorough understanding of its mechanical behaviour is thus important. In this study, the anisotropy of the shear modulus of natural Boom Clay samples was investigated using the bender element method. Seven samples located at different distances from the connecting gallery of the HADES underground research laboratory were tested for shearing in three different directions with respect to the bedding plane. The results obtained confirm the mechanical anisotropy of Boom Clay. Furthermore, the values of small-strain shear modulus in the near field of the gallery were found to be lower than those in the far field, suggesting that the mechanical properties of Boom Clay remain affected by gallery excavation damage that occurred more than 10 years ago.
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Anisotropic thermal conductivity of natural Boom Clay
Applied Clay Science, 2014Co-Authors: Linh Quyen Dao, Pierre Delage, Anh Minh Tang, Yu-jun Cui, Jean-michel Pereira, Xavier SillenAbstract:The thermal conductivity of host rocks is an important parameter in the design of deep geological disposal of heat-emitting radioactive waste. Due to bedding, heat transfer in sedimentary rocks is affected by their transversally isotropic structure. In this work, an experimental program is run to measure the thermal conductivities of Boom Clay along various orientations with respect to the bedding plane by using the needle thermal probe technique. Measurements were performed on specimens obtained from cores drilled from the HADES Underground Research Laboratory (URL) at Mol, Belgium, at a depth of 223 m. The thermal conductivity values obtained are in good agreement with those previously published, confirming the thermal anisotropy of Boom Clay. Moreover, the observed changes in thermal conductivity with respect to the distance to the gallery provide further evidence on the extent of the Excavation Damaged Zone around the gallery.
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An Experimental Study on the Secondary Deformation of Boom Clay
Applied Clay Science, 2012Co-Authors: Yongfeng Deng, Yu-jun Cui, Anh Minh Tang, Xavier SillenAbstract:Boom Clay formation, a deposit of slightly over-consolidated marine Clay that belongs to the Oligocene series in the north east of Belgium, has been selected as a possible host material of nuclear waste disposal. In this context, the long-term deformation behaviour of Boom Clay is of crucial importance in the performance assessment of the whole storage system. In this study, low and high pressure oedometer tests are carried out; the e-log σ'v (void ratio - logarithm of vertical effective stress) and e-log t (void ratio - logarithm of time) curves obtained are used to determine the compression index Cc*, swelling index Cs* and secondary deformation coefficient Cα during both loading and unloading. The relationship between Cα and the effective stress ratio (σ'v/σ'c, vertical effective stress to pre-consolidation stress) is analysed, and it is observed that C increases linearly with log σ'v/ σ'c. Examination of the ratio of Cα/Cc* for various soils shows that the secondary deformation behaviour of Boom Clay is similar to that of shake and mudstone. The relation between Cα and Cc* is linear; but the relation between Cα and Cs* is bi-linear. The bi-linearity observed is related to two different mechanisms: the mechanically dominated rebounding and the physico-chemically dominated swelling.