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A note on thermomechanical anisotropy of clays
PROPERTIES:PHYSICO-CHEMICAL the activation energy is fairly high, meaning that the conversion is negligible at temperatures lower than about 60°C. (from Authors)
966128 Thermomechanical properties of deep argillaceous formations C. Del Olmo, V. Fioravante, F. Gera, T. Hueckel, J. C. Mayor & R. Pellegrini, Engineering Geology, 41(1-4), 1996, pp 87-102. A relationship is developed to link strength and the maximum preconsolidation stress to the initial void ratio and carbonate content. Compressibility is also correlated to carbonates. Thermal strains in drained and undrained conditions for a Spanish, a Belgian and an Italian natural clay are compared. In the elastic state strains are comparable, while in the plastic range thermal strains are highest for the Belgian clay, lower in the Spanish cemented clay and lowest in the Italian clay, very stiff and cemented. (from Authors) 966129 Modelling of the physical behaviour of clay barriers close to water saturation L. Borgesson, O. Karnland & L.-E. Johannesson, Engineering Geology, 41(1-4), 1996, pp 127-144. The physical properties of bentonite-based buffer materials for nuclear waste repositories have been investigated by a number of different laboratory tests. These tests have yielded a material model that is valid for conditions close to water saturation and is useful for describing: 1) the stress, strain and volume change behaviour; 2) the pore pressure and flow of water; and 3) the thermal and thermomechanical response. The material model is based on the Drucker-Prager plasticity model and a Porous Elastic Model. The paper presents some laboratory results that are the basis of the first model. (from Authors) 966130 A constitutive thermomechanical model for saturated clays J.-C. Robinet, A. Rahbaoui, F. Plas & P. Lebon, Engineering Geology, 41(1-4), 1996, pp 145-169. This paper suggests a formulation of a model of thermoelasto-plastic behaviour of non-expansive saturated clays characterised by two plastic mechanisms. The mechanical yield surfacefrm of the contact-stress mechanism is based on a modified cam-clay model; the thermal softening yield surface f r is a plane separating two thermal domains. In normally consolidated conditions, the resulting response to an increase of temperature is compressive. However, in highly overconsolidated conditions, a small irreversible dilative volumetric strain is observed when the temperature is above a threshold value. The constitutive model combines thermomechanical hardening, predominant in normally consolidated states and absent in overconsolidated states where the thermal softening occurs. Some numerical simulations of thermomechanical tests on remoulded Boom, "Bassin Parisien' and Pontida clays are presented. (from Authors) 966131 A note on thermomechanical anisotropy of clays T. Hueckel & R. Pellegrini, Engineering Geology, 41(1-4), 1996, pp 171-180. Deep clays exhibit a pronounced strain anisotropy both during mechanical loading as well as during heating and cooling at constant stress in drained isotropic conditions. During mechanical loading vertical strain is larger than the horizontal one. During heating the vertical strain is larger than the horizontal one within the elastic range; the opposite is observed in the elasto-plastic range. The above described response can be interpreted adopting a consistent rotational, kinematic hardening thermo-elasto-plastic constitutive law. (Authors)
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966132 Evaluation of coupled heat and moisture flow parameters in a bentonite-sand buffer material R. N. Yong & A.-M. O. Mohamed, Engineering Geology, 41(1-4), 1996, pp 269-286. Several series of one-dimensional tests were used to study the nature of transient heat and moisture movements in a clay buffer under different imposed temperature gradients. The measured temperature and moisture profiles were used to calculate the diffusion parameters governing heat and moisture movement in the buffer material. The experimentally determined diffusion parameters are shown to be dependent on the moisture content and temperature. (from Authors) 966133 Effects of heat/water flow interaction on compacted bentonite: prefiminary results M. V. Villar, J. Cuevas & P. L. Martin, Engineering Geology, 41(1-4), 1996, pp 257-267. Compacted bentonite blocks have been heated and hydrated in a stainless steel cell in order to simulate, in the laboratory, the conditions of the clay barrier in a high-level radioactive waste repository. For the periods of time considered (up to 2500 h), the hydration process is not affected by the thermal gradient, the high suction of the bentonite being the critical factor in the initial water uptake of the clay barrier. A remarkable saline environment has been detected near the heater, due to salt migration towards dried areas. (from Authors) 966134 Moisture movement under a temperature gradient in highly compacted bentonite T. Kanno, K. Kato & J. Yamagata, Engineering Geology, 41(1-4), 1996, pp 287-300. The heat induced moisture movement in buffer materials to be used for the geological disposal of high-level radioactive waste is investigated by a series of experiments and numerical simulations. Highly compacted blocks of Japanese Na bentonite are used in the experiments as the buffer materials. Mechanistic models are formulated to the finite-element program which are applied to interpret the experimental results. The applicability of the mechanistic models to the compacted bentonite is examined. The numerical results agree well with the experimental results qualitatively, though a few quantitative discrepancies are found. (from Authors) 966135 On the development of a model of the thermo-mechanicalhydraulic behaviour of unsaturated soils H. R. Thomas, Y. He, M. R. Sansom & C. L. W. Li, Engineering Geology, 41(1-4), 1996, pp 197-218. A step by step approach is adopted, taking as a starting point a potential-based model of coupled heat and moisture transfer. Extensions of this work to include the effect of air transfer and the deformation characteristics of the soil are presented. Constitutive relationships which accommodate non-linear elasticity, thermoelasticity and elasto-plasticity are considered. Numerical solutions of the various versions of the model are presented. (from Authors) 966136 Effects of temperature on strength and compressibility of sand-bentonite buffer B. E. Lingnau, J. Graham, D. Yarechewski, N. Tanaka & M. N. Gray, Engineering Geology, 41(1-4), 1996, pp 103-115. Dense sand-bentonite buffer is proposed as one barrier for isolating nuclear fuel waste. The buffer will be required to function under conditions of high total pressures and elevated temperatures approaching 100°C. Summary results are presented from two test programs: 1) isothermal consolidated undrained triaxial tests; and 2) isothermal drained constant-p' triaxial tests. The results indicate parallel hardening lines at systematically lower values of specific volume at elevated
966128 Thermomechanical properties of deep argillaceous formations C. Del Olmo, V. Fioravante, F. Gera, T. Hueckel, J. C. Mayor & R. Pellegrini, Engineering Geology, 41(1-4), 1996, pp 87-102. A relationship is developed to link strength and the maximum preconsolidation stress to the initial void ratio and carbonate content. Compressibility is also correlated to carbonates. Thermal strains in drained and undrained conditions for a Spanish, a Belgian and an Italian natural clay are compared. In the elastic state strains are comparable, while in the plastic range thermal strains are highest for the Belgian clay, lower in the Spanish cemented clay and lowest in the Italian clay, very stiff and cemented. (from Authors) 966129 Modelling of the physical behaviour of clay barriers close to water saturation L. Borgesson, O. Karnland & L.-E. Johannesson, Engineering Geology, 41(1-4), 1996, pp 127-144. The physical properties of bentonite-based buffer materials for nuclear waste repositories have been investigated by a number of different laboratory tests. These tests have yielded a material model that is valid for conditions close to water saturation and is useful for describing: 1) the stress, strain and volume change behaviour; 2) the pore pressure and flow of water; and 3) the thermal and thermomechanical response. The material model is based on the Drucker-Prager plasticity model and a Porous Elastic Model. The paper presents some laboratory results that are the basis of the first model. (from Authors) 966130 A constitutive thermomechanical model for saturated clays J.-C. Robinet, A. Rahbaoui, F. Plas & P. Lebon, Engineering Geology, 41(1-4), 1996, pp 145-169. This paper suggests a formulation of a model of thermoelasto-plastic behaviour of non-expansive saturated clays characterised by two plastic mechanisms. The mechanical yield surfacefrm of the contact-stress mechanism is based on a modified cam-clay model; the thermal softening yield surface f r is a plane separating two thermal domains. In normally consolidated conditions, the resulting response to an increase of temperature is compressive. However, in highly overconsolidated conditions, a small irreversible dilative volumetric strain is observed when the temperature is above a threshold value. The constitutive model combines thermomechanical hardening, predominant in normally consolidated states and absent in overconsolidated states where the thermal softening occurs. Some numerical simulations of thermomechanical tests on remoulded Boom, "Bassin Parisien' and Pontida clays are presented. (from Authors) 966131 A note on thermomechanical anisotropy of clays T. Hueckel & R. Pellegrini, Engineering Geology, 41(1-4), 1996, pp 171-180. Deep clays exhibit a pronounced strain anisotropy both during mechanical loading as well as during heating and cooling at constant stress in drained isotropic conditions. During mechanical loading vertical strain is larger than the horizontal one. During heating the vertical strain is larger than the horizontal one within the elastic range; the opposite is observed in the elasto-plastic range. The above described response can be interpreted adopting a consistent rotational, kinematic hardening thermo-elasto-plastic constitutive law. (Authors)
257A
966132 Evaluation of coupled heat and moisture flow parameters in a bentonite-sand buffer material R. N. Yong & A.-M. O. Mohamed, Engineering Geology, 41(1-4), 1996, pp 269-286. Several series of one-dimensional tests were used to study the nature of transient heat and moisture movements in a clay buffer under different imposed temperature gradients. The measured temperature and moisture profiles were used to calculate the diffusion parameters governing heat and moisture movement in the buffer material. The experimentally determined diffusion parameters are shown to be dependent on the moisture content and temperature. (from Authors) 966133 Effects of heat/water flow interaction on compacted bentonite: prefiminary results M. V. Villar, J. Cuevas & P. L. Martin, Engineering Geology, 41(1-4), 1996, pp 257-267. Compacted bentonite blocks have been heated and hydrated in a stainless steel cell in order to simulate, in the laboratory, the conditions of the clay barrier in a high-level radioactive waste repository. For the periods of time considered (up to 2500 h), the hydration process is not affected by the thermal gradient, the high suction of the bentonite being the critical factor in the initial water uptake of the clay barrier. A remarkable saline environment has been detected near the heater, due to salt migration towards dried areas. (from Authors) 966134 Moisture movement under a temperature gradient in highly compacted bentonite T. Kanno, K. Kato & J. Yamagata, Engineering Geology, 41(1-4), 1996, pp 287-300. The heat induced moisture movement in buffer materials to be used for the geological disposal of high-level radioactive waste is investigated by a series of experiments and numerical simulations. Highly compacted blocks of Japanese Na bentonite are used in the experiments as the buffer materials. Mechanistic models are formulated to the finite-element program which are applied to interpret the experimental results. The applicability of the mechanistic models to the compacted bentonite is examined. The numerical results agree well with the experimental results qualitatively, though a few quantitative discrepancies are found. (from Authors) 966135 On the development of a model of the thermo-mechanicalhydraulic behaviour of unsaturated soils H. R. Thomas, Y. He, M. R. Sansom & C. L. W. Li, Engineering Geology, 41(1-4), 1996, pp 197-218. A step by step approach is adopted, taking as a starting point a potential-based model of coupled heat and moisture transfer. Extensions of this work to include the effect of air transfer and the deformation characteristics of the soil are presented. Constitutive relationships which accommodate non-linear elasticity, thermoelasticity and elasto-plasticity are considered. Numerical solutions of the various versions of the model are presented. (from Authors) 966136 Effects of temperature on strength and compressibility of sand-bentonite buffer B. E. Lingnau, J. Graham, D. Yarechewski, N. Tanaka & M. N. Gray, Engineering Geology, 41(1-4), 1996, pp 103-115. Dense sand-bentonite buffer is proposed as one barrier for isolating nuclear fuel waste. The buffer will be required to function under conditions of high total pressures and elevated temperatures approaching 100°C. Summary results are presented from two test programs: 1) isothermal consolidated undrained triaxial tests; and 2) isothermal drained constant-p' triaxial tests. The results indicate parallel hardening lines at systematically lower values of specific volume at elevated