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Numerical investigation of the structure of persistent shear bands in granular media
239A 924264 Verification studies on the UDEC computational model of jointed rock Brady, B H; Hsiung, S H; Chowdhury, A H; Philip, J Proc International Conference on Mechanics of Jointed and Fanlted Rock, Vienna, 18-20 April 1990 P551-558. Publ Rotterdam: A A Balkema, 1990 Numerical models of jointed rock masses must be able to represent both the discontinuous behaviour of such a medium and continuous bchaviour of individual blocks of which the medium is composed. The capability of the distinct element code UDEC is examined by comparing its predictions to analytical solutions for benchmark problems, cyclic loading of a specimen with a slipping joint, a circular opening intersected by a joint, and slip in a jointed body induced by a harmonic shear wave. Results indicate UDEC is suitable for modelling both static and dynamic behaviour of jointed rocks.
Stress analysis See also: 924051, 924098
the optimization strategy for FEM simulation, until the objective function has reached a sufficiently small value. The calibration procedure is also illustrated using cavity expansion data. 924268 Deformability of intact rock Ofoegbu, G I; Curran, J H lnt J Rock Mech Min Sci 1/29, N1. Jan 1992, P35-48 A constitutive model to describe the incremental stiffness of rock under general loading paths using elasticity, plasticity, and continuum damage mechanics bases is presented. Rock strength and elastic deformability are described in terms of a transformed stress tensor, with a continuum damage variable accounting for the effects of microcracks on the ability of the rock to carry distortional loads. The rock properties required by the model are tensile strength, elastic stiffness, shear resistance, and dilation ratio, the last three of which are functions of deformation and confinement. These properties have been evaluated for Creighton norite from triaxial test data. The model, when implemented with the finite element code ABAQUS, accurately reproduces test data.
924265 Mechanics of partially saturated soils Pietruszczak, S; Pande, G N Comput Geotech VI2, NI, 1991, P55-71
924269 Elastic material constants for isotropic granular solids with particle rotation Chang, C S; Ma, L lnt J Solids Struct V29, 178, 1992, P1001-1018
A model is presented to describe the undrained behaviour of a partially saturated soil, which is treated as a 3 phase (liquid, gas, skeleton) system, with liquid and gas phases separated by curved boundaries across which pressure is discontinuous as a result of surface tension effects. The gas is trapped within a continuous liquid phase. It is formulated using as a basis a rule of decomposition of stresses in saturated soils based on average stress measures in its constituents. Average pore size is included as an independent variable which governs evolution of suction pressure in the soil.
A granular material is modelled as a micropolar continuum, taking account of particle interaction and microstructure of the material. Constitutive constants are derived in terms of elastic interparticle stiffness for a granular solid with isotropic random fabric distribution. Six material constants are identified, as compared to two in conventional elasticity, and their physical meaning discussed with emphasis on the role of particle spin. A finite element formulation is presented to show the effects of these constants and interparticle properties on deformation behaviour of granular solids in general boundary value problems.
924266 Numerical investigation of the structure of persistent shear bands in granular media Bardet, J P; Proubet, J Geotechnique V41, N4, Dec 1991, P599-613 Shear band formation is a feature of deformation in granular media. The structure of persistent shear bands has been studied with numerical simulation of a 2 dimensional assembly of circular disks of two diameters. Displacement, volume strain, void ratio, rotations of the particles and their neighborhoods, and contact orientation have been examined within the shear band. The simulations indicate the importance of particle rotations inside the shear band and support the micropolar description of granular materials. 924267 Computer-aided calibration of a soil plasticity model Anandarajah, A; Agarwal, D lnt J Num Anal Meth Geomech VI5, NI2, Dec 1991, P835856 Properties obtained directly from in situ data are more representative of a field soil than those from laboratory testing. A nonlinear optimization technique is presented for back calculation of model parameters for a simple bounding surface plasticity model from field pressuremeter data. In situ soil response is input, initial values of model parameters chosen,response predicted by finite element analysis, the objective function evaluated, and new values of parameters selected by
924270 Reformation of the equations of anisotropic poroelasticity Thompson, M; Willis, J R J Appl Mech (Trans ASME Set E) II58, N3, Sept 1991, P612-616 Many rock materials behave in an anisotropic, nonlinear manner and include inhomogeneities on a microscale. Constitutive equations describing the incremental behaviour of an anisotropic poroelastic material are presented, which treat the anisotropic poroelasticity in terms of material tensors. The tensors are defined from stress field and pore fluid content changes produced by boundary displacements compatible with uniform mean strain and uniform pore pressure increments. This leads to homogeneous deformation on scales significantly larger than the length scale of microstructural inhomogeneities. The parameters for the model can be obtained from standard laboratory tests. The case of transverse isotropy is illustrated. 924271 Flow-deformation response of dual-porosity media Elsworth, D; Bai, M J Geotech Engng Div ASCE VII8, NI, Jan 1992, P107-124 A constitutive model is presented for linear poroelastic behaviour of a fissured porous medium. It requires a stress strain relation and two equations representing conservation of mass. Behaviour is defined in terms of parameters of the intact matrix and surrounding fracture system. Pore pressures and
© 1992 Pergamon Press Ltd. Reproduction not permitted
Stress analysis See also: 924051, 924098
the optimization strategy for FEM simulation, until the objective function has reached a sufficiently small value. The calibration procedure is also illustrated using cavity expansion data. 924268 Deformability of intact rock Ofoegbu, G I; Curran, J H lnt J Rock Mech Min Sci 1/29, N1. Jan 1992, P35-48 A constitutive model to describe the incremental stiffness of rock under general loading paths using elasticity, plasticity, and continuum damage mechanics bases is presented. Rock strength and elastic deformability are described in terms of a transformed stress tensor, with a continuum damage variable accounting for the effects of microcracks on the ability of the rock to carry distortional loads. The rock properties required by the model are tensile strength, elastic stiffness, shear resistance, and dilation ratio, the last three of which are functions of deformation and confinement. These properties have been evaluated for Creighton norite from triaxial test data. The model, when implemented with the finite element code ABAQUS, accurately reproduces test data.
924265 Mechanics of partially saturated soils Pietruszczak, S; Pande, G N Comput Geotech VI2, NI, 1991, P55-71
924269 Elastic material constants for isotropic granular solids with particle rotation Chang, C S; Ma, L lnt J Solids Struct V29, 178, 1992, P1001-1018
A model is presented to describe the undrained behaviour of a partially saturated soil, which is treated as a 3 phase (liquid, gas, skeleton) system, with liquid and gas phases separated by curved boundaries across which pressure is discontinuous as a result of surface tension effects. The gas is trapped within a continuous liquid phase. It is formulated using as a basis a rule of decomposition of stresses in saturated soils based on average stress measures in its constituents. Average pore size is included as an independent variable which governs evolution of suction pressure in the soil.
A granular material is modelled as a micropolar continuum, taking account of particle interaction and microstructure of the material. Constitutive constants are derived in terms of elastic interparticle stiffness for a granular solid with isotropic random fabric distribution. Six material constants are identified, as compared to two in conventional elasticity, and their physical meaning discussed with emphasis on the role of particle spin. A finite element formulation is presented to show the effects of these constants and interparticle properties on deformation behaviour of granular solids in general boundary value problems.
924266 Numerical investigation of the structure of persistent shear bands in granular media Bardet, J P; Proubet, J Geotechnique V41, N4, Dec 1991, P599-613 Shear band formation is a feature of deformation in granular media. The structure of persistent shear bands has been studied with numerical simulation of a 2 dimensional assembly of circular disks of two diameters. Displacement, volume strain, void ratio, rotations of the particles and their neighborhoods, and contact orientation have been examined within the shear band. The simulations indicate the importance of particle rotations inside the shear band and support the micropolar description of granular materials. 924267 Computer-aided calibration of a soil plasticity model Anandarajah, A; Agarwal, D lnt J Num Anal Meth Geomech VI5, NI2, Dec 1991, P835856 Properties obtained directly from in situ data are more representative of a field soil than those from laboratory testing. A nonlinear optimization technique is presented for back calculation of model parameters for a simple bounding surface plasticity model from field pressuremeter data. In situ soil response is input, initial values of model parameters chosen,response predicted by finite element analysis, the objective function evaluated, and new values of parameters selected by
924270 Reformation of the equations of anisotropic poroelasticity Thompson, M; Willis, J R J Appl Mech (Trans ASME Set E) II58, N3, Sept 1991, P612-616 Many rock materials behave in an anisotropic, nonlinear manner and include inhomogeneities on a microscale. Constitutive equations describing the incremental behaviour of an anisotropic poroelastic material are presented, which treat the anisotropic poroelasticity in terms of material tensors. The tensors are defined from stress field and pore fluid content changes produced by boundary displacements compatible with uniform mean strain and uniform pore pressure increments. This leads to homogeneous deformation on scales significantly larger than the length scale of microstructural inhomogeneities. The parameters for the model can be obtained from standard laboratory tests. The case of transverse isotropy is illustrated. 924271 Flow-deformation response of dual-porosity media Elsworth, D; Bai, M J Geotech Engng Div ASCE VII8, NI, Jan 1992, P107-124 A constitutive model is presented for linear poroelastic behaviour of a fissured porous medium. It requires a stress strain relation and two equations representing conservation of mass. Behaviour is defined in terms of parameters of the intact matrix and surrounding fracture system. Pore pressures and
© 1992 Pergamon Press Ltd. Reproduction not permitted