Quarterly Journal of Engineering Geology and Hydrogeology, 44: 23-33, Jan 1, 2011
Rainfall is the most frequent triggering factor for landslides and the development of early warni... more Rainfall is the most frequent triggering factor for landslides and the development of early warning systems has to take account of this. It is suggested that direct measurement of pore pressure gives the most reliable prediction of failure of a slope. The amount of rainfall can be only a crude indicator of failure as the processes that occur between rain falling on a slope and the resulting pore water pressure change are complex, highly non-linear and hysteretic. The paper describes high capacity tensiometers developed within the EU-funded MUSE Research Training Network that have been used for measuring suctions in slopes. High-capacity tensiometers are capable of direct measurement of pore water pressure down to −2 MPa and are also able to record positive pore water pressures. Two methods of field installation are discussed; one developed by ENPC in France uses a single tensiometer per hole, and the second technique, developed by Durham University in the UK, allows multiple tensiometers to be used at different depths within a single borehole. Continuous monitoring of pore water pressure has been carried out over several months and shows the responses to climatic events.
73rd EAGE Conference and Exhibition incorporating SPE EUROPEC 2011, 2011
High stress oedometric compression tests (maximum 65 MPa) were carried out on samples of oil sand... more High stress oedometric compression tests (maximum 65 MPa) were carried out on samples of oil sand from Athabasca. X-Ray microtomography observation suggested that the initially dense interlocked grain fabric of the natural specimen has been altered by extraction, stress release, temperature change, storage, transport and sample trimming, resulting in a clearly apparent micro-crack network. Some time dependent effects that overestimated sample compressibility were observed when using the standard step loading procedures and a procedure with short steps (5 mn instead of 24 h) appeared to be better adapted. At low stresses, the sample disturbance appeared to overestimate the sand compressibility and it is suggested that better parameters could be obtained once submitting the sample to the maximum stress supported during its geological history (here 24 MPa). Grain crushing at high stresses was also evidenced and the role of grain crushing during the history of the deposit was also commented.
Pre-compacted bentonite bricks are often considered as sealing/backfill elements in deep geologic... more Pre-compacted bentonite bricks are often considered as sealing/backfill elements in deep geological repositories for high level radioactive waste. A good understanding of their microstructure changes upon hydration is essential as the microstructure changes are directly related to the macroscopic hydro-mechanical behaviour. In this study, the microstructure features of the compacted MX80 bentonite used as a sealing material in a field experiment were characterized by means of both mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Emphasis was put on the effects of final dry density (density after swelling) and hydration time. The results obtained show that the changes in soil porosity upon swelling are mainly due to the increase in large-pores of about 50 mm diameter and medium-pores of 1 mm diameter. In addition, the microstructure changed over time due to the water re-distribution that occurred among each level of pores: the volume of both the large-pores and small-pores decreased along as the volume of the medium-pores increased. A uniform microstructure can be then expected in the long term. Furthermore, it was observed that the higher the final dry density, the slower the microstructure changes.
Cet article présente une méthode d'évaluation de la perméabilité d'une argile peu perméable (argi... more Cet article présente une méthode d'évaluation de la perméabilité d'une argile peu perméable (argile de Boom) à partir d'un essai de compression isotrope en régime transitoire. Pour ce faire, un échantillon cylindrique d'argile de Boom est placé dans une cellule triaxiale et soumis à une pression interstitielle constante à l'une de ses extrémités. L'augmentation de la pression de confinement à vitesse contrôlée provoque l'accroissement de la pression interstitielle, qu'on mesure à l'autre extrémité de l'échantillon. La perméabilité de l'argile est évaluée en développant une méthode d'identification inverse d'un problème de diffusion de pression dans le milieu poreux.
To study the interlayer creation and the mud-pumping phenomena in the conventional French railway... more To study the interlayer creation and the mud-pumping phenomena in the conventional French railway substructure, a physical model was developed with a 160-mm-thick ballast layer overlaying a 220-mm-thick artificial silt layer (mixture of crushed sand and kaolin), both layers being compacted in a transparent cylinder of a 550-mm-inner diameter. One positive pore water pressure sensor, three tensiometers, and three time domain reflectometer (TDR) sensors were installed around the ballast/silt interface allowing the evolution of pore water pressure (negative or positive) and volumetric water content to be monitored, respectively. A digital camera was installed allowing direct monitoring of different movements (ballast, ballast/subsoil interface, etc.). The effects of loading (monotonic and cyclic loadings) and degree of saturation of subsoil (w ¼ 16 %, S r ¼ 55 %, and near-saturation state) were investigated. It was found that the development of pore water pressure in the subsoil is the key factor causing the migration of fine particles, hence, resulting in the creation of interlayer, as well as mud pumping. In particular, the camera exposed the pumping up level of fine particles during the test, showing that the migration of fine particles was not only a result of the interpenetration of ballast particles and subsoil, but also of the pore water pressure that pushed the fine particle upward. The quality of the recorded data showed that the physical model developed worked well and the test protocol adopted for studying the mechanisms of intermixing of ballast and subsoil and mud pumping was appropriate.
Boom Clay is considered to be a potential host formation for a geological repository of radioacti... more 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.
Samples have a porosity from 37 % to 40 % (deduced from results of Tomography scanner, MicroTomog... more Samples have a porosity from 37 % to 40 % (deduced from results of Tomography scanner, MicroTomography scanner, Purcell tests and from weight measurements) and a high permeability of about 3 to 4.10 -12 m² (3 to 4 ABSTRACT: Most of thermal heavy oil recovery methods entails changes of pore fluid, pressure and temperature (pore fluid viscosity) which in turn induce complex changes in the elastic properties of reservoirs (in general, unconsolidated or weakly consolidated reservoirs). In this paper, laboratory measurements of velocities and attenuations at different conditions of temperature and stress were performed on weakly consolidated reconstituted sandstones saturated with various fluids (air, water and glycerol). The reconstituted sandstones are representative models of weakly cemented sandstone reservoirs with porous and highly permeable nature. The experimental results demonstrate the strong impact of different pore fluids on the compressional and shear wave velocities and attenuations. The influence of temperature and pressure and also wave dispersion mechanisms are discussed.
Quarterly Journal of Engineering Geology and Hydrogeology, 44: 23-33, Jan 1, 2011
Rainfall is the most frequent triggering factor for landslides and the development of early warni... more Rainfall is the most frequent triggering factor for landslides and the development of early warning systems has to take account of this. It is suggested that direct measurement of pore pressure gives the most reliable prediction of failure of a slope. The amount of rainfall can be only a crude indicator of failure as the processes that occur between rain falling on a slope and the resulting pore water pressure change are complex, highly non-linear and hysteretic. The paper describes high capacity tensiometers developed within the EU-funded MUSE Research Training Network that have been used for measuring suctions in slopes. High-capacity tensiometers are capable of direct measurement of pore water pressure down to −2 MPa and are also able to record positive pore water pressures. Two methods of field installation are discussed; one developed by ENPC in France uses a single tensiometer per hole, and the second technique, developed by Durham University in the UK, allows multiple tensiometers to be used at different depths within a single borehole. Continuous monitoring of pore water pressure has been carried out over several months and shows the responses to climatic events.
73rd EAGE Conference and Exhibition incorporating SPE EUROPEC 2011, 2011
High stress oedometric compression tests (maximum 65 MPa) were carried out on samples of oil sand... more High stress oedometric compression tests (maximum 65 MPa) were carried out on samples of oil sand from Athabasca. X-Ray microtomography observation suggested that the initially dense interlocked grain fabric of the natural specimen has been altered by extraction, stress release, temperature change, storage, transport and sample trimming, resulting in a clearly apparent micro-crack network. Some time dependent effects that overestimated sample compressibility were observed when using the standard step loading procedures and a procedure with short steps (5 mn instead of 24 h) appeared to be better adapted. At low stresses, the sample disturbance appeared to overestimate the sand compressibility and it is suggested that better parameters could be obtained once submitting the sample to the maximum stress supported during its geological history (here 24 MPa). Grain crushing at high stresses was also evidenced and the role of grain crushing during the history of the deposit was also commented.
Pre-compacted bentonite bricks are often considered as sealing/backfill elements in deep geologic... more Pre-compacted bentonite bricks are often considered as sealing/backfill elements in deep geological repositories for high level radioactive waste. A good understanding of their microstructure changes upon hydration is essential as the microstructure changes are directly related to the macroscopic hydro-mechanical behaviour. In this study, the microstructure features of the compacted MX80 bentonite used as a sealing material in a field experiment were characterized by means of both mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Emphasis was put on the effects of final dry density (density after swelling) and hydration time. The results obtained show that the changes in soil porosity upon swelling are mainly due to the increase in large-pores of about 50 mm diameter and medium-pores of 1 mm diameter. In addition, the microstructure changed over time due to the water re-distribution that occurred among each level of pores: the volume of both the large-pores and small-pores decreased along as the volume of the medium-pores increased. A uniform microstructure can be then expected in the long term. Furthermore, it was observed that the higher the final dry density, the slower the microstructure changes.
Cet article présente une méthode d'évaluation de la perméabilité d'une argile peu perméable (argi... more Cet article présente une méthode d'évaluation de la perméabilité d'une argile peu perméable (argile de Boom) à partir d'un essai de compression isotrope en régime transitoire. Pour ce faire, un échantillon cylindrique d'argile de Boom est placé dans une cellule triaxiale et soumis à une pression interstitielle constante à l'une de ses extrémités. L'augmentation de la pression de confinement à vitesse contrôlée provoque l'accroissement de la pression interstitielle, qu'on mesure à l'autre extrémité de l'échantillon. La perméabilité de l'argile est évaluée en développant une méthode d'identification inverse d'un problème de diffusion de pression dans le milieu poreux.
To study the interlayer creation and the mud-pumping phenomena in the conventional French railway... more To study the interlayer creation and the mud-pumping phenomena in the conventional French railway substructure, a physical model was developed with a 160-mm-thick ballast layer overlaying a 220-mm-thick artificial silt layer (mixture of crushed sand and kaolin), both layers being compacted in a transparent cylinder of a 550-mm-inner diameter. One positive pore water pressure sensor, three tensiometers, and three time domain reflectometer (TDR) sensors were installed around the ballast/silt interface allowing the evolution of pore water pressure (negative or positive) and volumetric water content to be monitored, respectively. A digital camera was installed allowing direct monitoring of different movements (ballast, ballast/subsoil interface, etc.). The effects of loading (monotonic and cyclic loadings) and degree of saturation of subsoil (w ¼ 16 %, S r ¼ 55 %, and near-saturation state) were investigated. It was found that the development of pore water pressure in the subsoil is the key factor causing the migration of fine particles, hence, resulting in the creation of interlayer, as well as mud pumping. In particular, the camera exposed the pumping up level of fine particles during the test, showing that the migration of fine particles was not only a result of the interpenetration of ballast particles and subsoil, but also of the pore water pressure that pushed the fine particle upward. The quality of the recorded data showed that the physical model developed worked well and the test protocol adopted for studying the mechanisms of intermixing of ballast and subsoil and mud pumping was appropriate.
Boom Clay is considered to be a potential host formation for a geological repository of radioacti... more 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.
Samples have a porosity from 37 % to 40 % (deduced from results of Tomography scanner, MicroTomog... more Samples have a porosity from 37 % to 40 % (deduced from results of Tomography scanner, MicroTomography scanner, Purcell tests and from weight measurements) and a high permeability of about 3 to 4.10 -12 m² (3 to 4 ABSTRACT: Most of thermal heavy oil recovery methods entails changes of pore fluid, pressure and temperature (pore fluid viscosity) which in turn induce complex changes in the elastic properties of reservoirs (in general, unconsolidated or weakly consolidated reservoirs). In this paper, laboratory measurements of velocities and attenuations at different conditions of temperature and stress were performed on weakly consolidated reconstituted sandstones saturated with various fluids (air, water and glycerol). The reconstituted sandstones are representative models of weakly cemented sandstone reservoirs with porous and highly permeable nature. The experimental results demonstrate the strong impact of different pore fluids on the compressional and shear wave velocities and attenuations. The influence of temperature and pressure and also wave dispersion mechanisms are discussed.
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