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  • Articles  (121)
  • American Association for the Advancement of Science (AAAS)
  • American Association of Petroleum Geologists (AAPG)
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  • Wiley-Blackwell
  • 1995-1999  (121)
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  • 1998  (44)
  • 1996  (77)
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  • Geosciences  (121)
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  • Articles  (121)
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  • 1
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 29-48 
    ISSN: 0363-9061
    Keywords: hydraulic behaviour ; joint ; mechanics of joint ; joint degradation ; joint elements ; interface mechanics ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Constitutive laws for rock joints should be able to reproduce the fundamental mechanical behaviour of real joints, such as dilation under shear and strain softening due to surface asperity degradation. In this work, we extend the model of Plesha to include hydraulic behaviour. During shearing, the joint can experience dilation, leading to an initial increase in its permeability. Experiments have shown that the rate of increase of the permeability slows down as shearing proceeds, and, at later stages, the permeability could decrease again. The above behaviour is attributed to gouge production. The stress-strain relationship of the joint is formulated by appeal to classical theories of interface plasticity. It is shown that the parameters of the model can be estimated from the Barton-Bandis empirical coefficients; the Joint Roughness Coefficient (JRC) and the Joint Compresive strength (JSC). We further assume that gouge production is also related to the plastic work of the shear stresses, which enables the derivation of a relationship between the permeability of the joint and its mechanical aperture. The model is implemented in a finite element code (FRACON) developed by the authors for the simulation of the coupled thermal-hydraulic-mechanical behaviour of jointed rock masses. Typical laboratory experiments are simulated with the FRACON code in order to illustrate the trends predicted in the proposed model. © 1998 by John Wiley & Sons. Ltd.
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  • 2
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 229-238 
    ISSN: 0363-9061
    Keywords: inclined shaft ; stress distribution ; field stress ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: In this study, the vertical overburden pressure in the vicinity of an inclined circular underground opening is defined by relation to the geometry of the medium. The stresses around the opening consisting of six components are induced by geostatic field stress. In this regard, the inclined circular opening i.e. shaft changes the original stress condition and an interrupted region develops beneath it. Three zones are defined on a plane which is perpendicular to the axis of shaft. The mathematical expressions of vertical overburden stresses at these three zones are established, respectively. The example given in appendix demonstrates the variation of radial and tangential stresses around the inclined shaft. It is seen that the stress distributions in the third zone, which includes the interrupted region, beneith the shaft display different configurations than that of those obtained by undisturbed field stresses. In the interrupted region the stresses around the shaft linearly grow up due to increasing overburden pressure by radial distance from the periphery of the shaft. At the boundary of interrupted region stresses jump to the original values induced by field stresses. © 1998 John Wiley & Sons, Ltd.
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  • 3
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 197-227 
    ISSN: 0363-9061
    Keywords: elastoplasticity ; constitutive equation ; subloading surface model ; cyclic plasticity ; soil ; rotational hardening ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The subloading surface model fulfills the mechanical requirements for constitutive equations, i.e. the continuity condition, the smoothness condition and the work rate stiffness relaxation and describes pertinently the Masing effect. The constitutive equation of soils is formulated by introducing the subloading surface model and formulating the evolutional rule of rotational hardening for the description of anisotropy. The applicability of the constitutive equation to the prediction of real soil deformation behaviour is verified by predicting monotonic and cyclic loading behaviour of sands under drained and undrained conditions and comparing them with test data. © 1998 John Wiley & Sons, Ltd.
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  • 4
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 303-322 
    ISSN: 0363-9061
    Keywords: pile driving ; open-ended piles ; plugging mechanism ; one-dimensional modelling ; stress wave propagation ; finite element analysis ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The plugging mechanism of infinitely-long open-ended piles is examined using numerical simulation of the wave propagation inside the soil plug and pile. It is shown that the key parameters for the plugging mechanism are the pile radius, the shape of the impact load, the shear wave velocity of the soil inside the pile, and the friction at the pile-soil interface. Consequently, the tendency of the pile to plug during driving can be assessed prior to the driving process by consideration of these key parameters. Existing one-dimensional models for the shaft response of open-ended piles are discussed and an improved model is presented. The differences between using one-dimensional models and finite element models to simulate the plugging process are examined. The differences are found to vary with the key parameters. Pile-in-pile and lumped-mass one-dimensional models are found to give satisfactory performance for some parameter combinations, while for others an axisymmetric finite element model must be used. © 1998 John Wiley & Sons, Ltd.
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  • 5
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 425-447 
    ISSN: 0363-9061
    Keywords: closed-form solution ; transversely isotropic half-space ; Fourier transform ; Hankel transform ; rock anisotropy ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: We rederive and present the complete closed-form solutions of the displacements and stresses subjected to a point load in a transversely isotropic elastic half-space. The half-space is bounded by a horizontal surface, and the plane of transverse isotropy of the medium is parallel to the horizontal surface. The solutions are obtained by superposing the solutions of two infinite spaces, one acting a point load in its interior and the other being free loading. The Fourier and Hankel transforms in a cylindrical co-ordinate system are employed for deriving the analytical solutions. These solutions are identical with the Mindlin and Boussinesq solutions if the half-space is homogeneous, linear elastic, and isotropic. Also, the Lekhnitskii solution for a transversely isotropic half-space subjected to a vertical point load on its horizontal surface is one of these solutions. Furthermore, an illustrative example is given to show the effect of degree of rock anisotropy on the vertical surface displacement and vertical stress that are induced by a single vertical concentrated force acting on the surface. The results indicate that the displacement and stress accounted for rock anisotropy are quite different for the displacement and stress calculated from isotropic solutions. © 1998 John Wiley & Sons, Ltd.
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  • 6
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 575-595 
    ISSN: 0363-9061
    Keywords: contaminant transport ; variable density flow ; fractures ; leakage ; dispersion ; diffusion ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A numerical model for simulating flow and transport of contaminants with variable density in fractured porous media is presented. The non-linearities arising from the density variation and the velocty-dependent dispersion terms have been handled by Picard method. It is shown that the contaminant transport in a fractured porous medium is initially dominated by fractures. However, with time increasing, the contaminant concentration in porous blocks increases, due to the leakage of contaminant from the fracture network to the porous blocks. It is also shown that the high density of contaminant has a greater effect on its transport in the fracture network than in the porous blocks. © 1998 John Wiley & Sons, Ltd.
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  • 7
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 671-687 
    ISSN: 0363-9061
    Keywords: recurrent neural network ; residual soil ; shear behaviour ; simulation ; prediction ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Modelling of shear behaviour of residual soils is difficult in that there is a significant variability in constituents and structures of the soil. A Recurrent Neural Network (RNN) is developed for modelling shear behaviour of the residual soil. The RNN model appears very effective in modelling complex soil shear behaviour, due to its feedback connections from an hidden layer to an input layer. Two architectures of the RNN model are designed for training different sets of experimental data which include strain-controlled undrained tests and stress-controlled drained tests performed on a residual Hawaiian volcanic soil. A dynamic gradient descent learning algorithm is used to train the network. By training only part of the experimental data the network establishes neural connections between stress and strain relations. Although the soil exhibited significant variations in terms of shearing behaviour, the RNN model displays a strong capability in capturing these variabilities. Both softening and hardening characteristics of the soil are well represented by the RNN model. Isotropic and anisotropic consolidation conditions are precisely reflected by the RNN model. In undrained tests, pore water pressure responses at various loading stages are simultaneously simulated. With a RNN model designed for a special drained test, the network is able to capture abrupt changes in axial and volumetric strains during shearing courses. These good agreements between the measured data and the modelling results demonstrate the desired capability of the RNN model in representing a soil behaviour. © 1998 John Wiley & Sons, Ltd.
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  • 8
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 749-769 
    ISSN: 0363-9061
    Keywords: wellbore stability ; sand erosion ; sand production ; sand prediction ; radial flow ; poroelasticity ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper extends earlier work on sand erosion and presents an attempt to couple sand erosion to mechanical damage of rock around a wellbore. Porosity which evolves in time and space as surface erosion progresses, is chosen as the coupling parameter. Both rock elasticity and strength (cohesion) are assumed to depend on porosity in such a way that the material becomes weaker with increasing porosity. The mathematical model, consists of erosion equations, mixture flow equations and stress equilibrium equations, is solved numerically by Galerkin finite element method. Numerical results suggest that erosion, resulting in sand production, is high close to the free surface. Erosion is accompained by changes in porosity and a significant permeability increase. Erosion in the vicinity of the wellbore induces alterations in the mechanical behaviour of the medium. Weakening of rock stiffness leads to severe alteration of both effective stresses and pore pressure near the cavity. Since cohesion decreases with increasing porosity, one can also identify the time instant at which rock mechanical failure starts. © 1998 John Wiley & Sons, Ltd.
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  • 9
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 867-901 
    ISSN: 0363-9061
    Keywords: finite elements ; hydromechanical coupling ; fractured rock masses ; viscoplasticity ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This work presents a finite element implementation to treat the Hydromechanical Coupling (HM) in fractured rock masses under the framework of the so-called ‘equivalent continuum’ approach. The multilaminar concept, introduced by Zienkiewicz and Pande, is used to simulate the mechanical behaviour of both the intact rock and the families of fractures. In that concept, the non-linearities in the constitutive relations are dealt by means of fictitious viscoplasticity. In the present implementation, the mechanical behaviour of the fractures is modelled by means of Barton-Bandis model. The shear stress/shear displacement/dilatancy relationship is modelled as viscoplastic and the normal stress/normal displacement as non-linear viscoelastic. Flow along fractures is considered to occur as a sequence of permanent states. The permeability tensor of the equivalent continuum is determined from the hydraulic apertures, in accordance of Barton et al. From the numerical point of view, the basic aim of the work is the implementation of an efficient scheme to solve the above described problem. This is done by designing a self-adaptive time step control, transparent to the user, which determines the highest possible time step while assuming the conditions of precision, stability and convergence. The paper presents the numerical details of such scheme together with validation/comparative examples and the results obtained on the analysis of the fractured rock foundation of a hypothetical dam. © 1998 John Wiley & Sons, Ltd.
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  • 10
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 1021-1033 
    ISSN: 0363-9061
    Keywords: retaining wall ; interface ; finite element ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A series of finite element analyses have been undertaken to investigate the effects of interface properties on the behaviour of a vertical retaining wall and the deformation of the ground around it. The boundary between a rigid embedded wall and the soil is modelled with zero thickness interface elements. Uniform translation of the wall has been studied. The analyses show the predicted limiting active and passive pressure on the wall are dependent on the maximum wall friction angle and are in reasonable agreement with accepted approximate analytical solutions. The limiting pressure is independent of the stiffness and dilation properties of the interface elements. The dilation properties of the interface have a significant effect on the ground surface deformation around the wall. © 1998 John Wiley & Sons, Ltd.
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  • 11
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 1-27 
    ISSN: 0363-9061
    Keywords: expansive clay ; hydromechanics ; unsaturated soils ; nuclear waste ; in situ test ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: BACCHUS2 in situ isothermal wetting experiment has been analysed by means of a coupled flow-deformation approach. Backfill material, a mixture of Boom clay powder and high density pellets, has been extensively tested in the laboratory in order to determine its hydraulic and mechanical properties. Parameters of constitutive equations were derived from this experimental data base. Two mechanical constitutive models have been used in the simulation of the ‘in situ’ experiment: a state surface approach and an elastoplastic model. Calculations have shown several features of the hydration process which help to understand the behaviour of expansive clay barriers. Predictions using both models have been compared with each other and with actual measurement records. This has allowed a discussion of the comparative mertis of both approaches and the identification of some critical parameters of backfill behaviour. Overall agreement between calculations and field measurements is encouraging and shows the potential of the methods developed to model the behaviour of engineered clay barriers in the context of nuclear waste disposal. © 1998 by John Wiley & Sons, Ltd.
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  • 12
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 75-95 
    ISSN: 0363-9061
    Keywords: three-dimensional ; heat ; moisture ; air ; transfer ; unsaturated ; soil ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A new three-dimensional numerical model of coupled heat, moisture and air transfer in unsaturated soil is presented. In particular, the model accommodates moisture transfer in the form of liquid and vapour flow and heat transfer arising from conduction, convection and latent heat of vaporization. The bulk flow of dry air and the movement of air in a dissolved state are also included. The theoretical basis of the model, the finite element solution of the spatial terms and finite difference solution of the temporal terms are briefly presented. Attention is focused on the verification of the new numerical solution. This is achieved via comparisons with independent solutions of heat, moisture and air transfer in an unsaturated soil. The physical problem considered includes the highly non-linear hydraulic properties of sand. Thermal conductivity is also included as a function of soil moisture content. Excellent correlation of results is shown thus providing confidence in the new model.The new model is also applied to a number of test cases which illustrate the need for the development of a model which can fully include three-dimensional behaviour. In particular, three applications are presented each increasing in complexity. The first application illustrates three-dimensional heat transfer. This particular application is verified against existing commercial finite element software. Subsequent applications serve to illustrate how the coupled processes of heat moisture and air transfer combine to yield three-dimensional problems even within a simple geometric domain. Visualization of three-dimensional results is also addressed. © 1998 by John Wiley & Sons, Ltd.
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  • 13
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 175-196 
    ISSN: 0363-9061
    Keywords: shear crack ; singular integral equation ; excavation ; discontinuities ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The problem of the equilibrium of a plane with a circular hole and a shear crack is considered to model failure of an excavation (borehole or circular opening) in rocks weakened by discontinuities (planes of weakness). It is assumed that sliding occurs in a part of the plane of weakness when the Mohr-Coulomb friction criterion is satisfied due to the stress redistribution caused by the excavation. The method of singular integral equations is employed to solve the boundary value problem. Geomechanical problems concerning borehole breakout and rockburst caused by fault-opening interaction are discussed. © 1998 John Wiley & Sons, Ltd.
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  • 14
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 277-301 
    ISSN: 0363-9061
    Keywords: seepage ; flow rate ; drain ; tunnel ; optimization ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The known formulae of Freeze and Cherry, Polubarinova-Kochina, Vedernikov for flow rate during 2-D seepage into horizontal drains and axisymmetric flow into cavities are examined and generalized. The case of an empty drain under ponded soil surface is studied and existence of drain depth providing minimal seepage rate is presented. The depth is found exhibiting maximal difference in rate between a filled and an empty drain. 3-D flow to an empty semi-spherical cavity on an impervious bottom is analysed and the difference in rate as compared with a completely filled cavity is established. Rate values for slot drains in a two-layer aquifer are ‘inverted’ using the Schulgasser theorem from the Polubarinova-Kochina expressions for corresponding flow rates under a dam. Flow to a point sink modelling a semi-circular drain in a layered aquifer is treated by the Fourier transform method. For unsaturated flow the catchment area of a single drain is established in terms of the quasi-linear model assuming the isobaric boundary condition along the drain contour. Optimal shape design problems for irrigation cavities are addressed in the class of arbitrary contours with seepage rate as a criterion and cavity cross-sectional area as an isoperimetric restriction. © 1998 John Wiley & Sons, Ltd.
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  • 15
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 351-391 
    ISSN: 0363-9061
    Keywords: cone penetration testing ; sand ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The cone penetration test (CPT) is widely used, and although initially developed as a stratigraphic logging tool its excellent repeatability and accuracy offers a benchmark quantitative test for sand in particular. A continuing difficulty, however, is that the CPT does not measure any soil property directly, so that parameters of interest must be recovered from solution of an inverse boundary value problem, which is difficult. To date most CPT interpretations in sand have been based on very limited calibration testing carried out in large chambers on a few sands from which mappings are developed. But there are differences in the CPT response from one sand to another leaving the interpretation imprecise (and arguably even speculative) because these differences remain poorly understood. In this paper we use the familiar spherical cavity expansion analogy to the CPT including large strains and a good, critical-state-based, soil model to develop a pattern of behaviour which we then compare to some of the reference chamber test data. We find that one of the issues of dispute in the empirical interpretation methods, the so-called stress-level effect, is caused by neglect of elasticity and that there are several additional parameters of first-order significance to cavity expansion in sands. More generally, we show that the difference in CPT response between various chamber sands in predicted. Our results are cast in dimensionless form and the inversion illustrates that extreme care is required in interpreting CPT data if the in situ sand state is to be determined with precision approaching that suggested as achievable by the repeatability of the CPT data itself. Aspects requiring particular care in interpreting CPT data in sand are discussed. © 1998 John Wiley & Sons, Ltd.
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  • 16
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 449-475 
    ISSN: 0363-9061
    Keywords: consolidation ; heat transfer ; poroelasticity ; pore pressure ; coupled fields ; Laplace transform ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper presents a theoretical approach to analyse coupled, linear thermoporoelastic fields in a saturated porous medium under radial and spherical symmetry. The governing equations account for compressibility and thermal expansion of constituents, heat sink due to thermal dilatation of water and thermal expansion of the medium, and thermodynamically coupled heat-water flow. It has been reported in the literature that thermodynamically coupled heat-water flows known as thermo-osmosis and thermal filtration have the potential to significantly alter the flow fields in clay-rich barriers in the near field of a underground waste containment scheme. This study presents a mathematical model and examines the effects of thermo-osmosis and thermal-filtration on coupled consolidation fields in a porous medium with a cavity. Analytical solutions of the governing equations are presented in the Laplace transform space. A numerical inversion scheme is used to obtain the time-domain solutions for a cylindrical cavity in a homogeneous or a non-homogeneous medium. A closed form time-domain solution is presented for a spherical cavity in a homogeneous medium. Selected numerical solutions for homogeneous and non-homogeneous media show a significant increase in pore pressure and displacements due to the presence of thermodynamically coupled flows and a negligible influence on temperature. © 1998 John Wiley & Sons, Ltd.
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  • 17
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 421-423 
    ISSN: 0363-9061
    Keywords: Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
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  • 18
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 603-619 
    ISSN: 0363-9061
    Keywords: earthquakes ; stress-strain response ; downhole arrays ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Recordings from downhole accelerometer arrays offer unique insight into soil behavior and ground response during earthquakes. In this paper we present a scheme for interpolating displacement and acceleration measurements to provide approximations for subsurface shear strain and stress as continuous functions of time. Our suggested interpolating functions are constructed in such a way that the free surface boundary condition will always be satisfied and the interpolated displacement and acceleration remain finite for all depths. We also show how the functions can be adapted to represent layered soil profiles. Depending on the number of instruments in the downhole array, a truncated series of functions can be derived so that each represents a modal shape for the layered soil profile. The resulting approximations for strain and stress are considered more accurate and robust than previous approximations. © 1998 John Wiley & Sons, Ltd.
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  • 19
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 621-653 
    ISSN: 0363-9061
    Keywords: state parameter ; stress-state relation ; constitutive modelling ; plasticity ; critical state ; sand and clay ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The purpose of this paper is to present a simple, unified critical state constitutive model for both clay and sand. The model, called CASM (Clay And Sand Model), is formulated in terms of the state parameter that is defined as the vertical distance between current state (v, p′) and the critical state line in v-ln p′ space. The paper first shows that the standard Cam-clay models (i.e. the original and modified Cam-clay models) can be reformulated in terms of the state parameter. Although the standard Cam-clay models prove to be successful in modelling normally consolidated clays, it is well known that they cannot predict many important features of the behavior of sands and overconsolidated clays. By adopting a general stress ratio-state parameter relation to describe the state boundary surface of soils, it is shown that a simple, unified constitutive model (CASM) can be developed for both clay and sand. It is also demonstrated that the standard Cam-clay yield surfaces can be either recovered or approximated as special cases of the yield locus assumed in CASM.The main feature of the proposed model is that a single set of yield and plastic potential functions has been used to model the behaviour of clay and sand under both drained and undrained loading conditions. In addition, it is shown that the behaviour of overconsolidated clays can also be satisfactorily modelled. Simplicity is a major advantage of the present state parameter model, as only two new material constants need to be introduced when compared with the standard Cam-clay models. © 1998 John Wiley & Sons, Ltd.
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  • 20
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 855-865 
    ISSN: 0363-9061
    Keywords: anchor ; trapdoor ; limit load ; cohesionless ; associative ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A methodology for determining the plane strain limit load acting on an anchor or trapdoor buried within a purely associative Coulomb soil is presented. True lower bounds derived from a family of limiting stress fields appropriate to shallow horizontal trapdoors and anchors are shown to correlate to within less than 1 percent of upper bounds available in the literature, permitting the true limit load to be almost exactly defined. The solution form alters for deeply buried anchors and trapdoors resulting in poorer correlations. Methods by which the work may be extended to cover the more practical instances of non-associative Coulomb soils are indicated but are beyond the scope of the current paper. © 1998 John Wiley & Sons, Ltd.
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  • 21
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 903-919 
    ISSN: 0363-9061
    Keywords: hollow cylinders ; diffuse mode bifurcations ; geomaterials ; non-normality ; pressure-sensitivity ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper derives analytically the condition for the onset of diffuse mode bifurcations in thick-walled hollow cylinders with internal radius a, external radius b and length L under axial compression and confining pressure. The thick-walled cylindrical specimens are made of geomaterial characterized by Rudnicki's constitutive model, and the method of solution for the governing equations is the velocity potential approach employed by Chau. Numerical results show that thick-walled cylinders are stronger than thin-walled cylinders against diffuse mode bifurcations, including both buckling, axisymmetric and non-axisymmetric deformations. In contrast to the conclusion for solid cylinders (Chau), no buckling solution is found for γ = mπa / L smaller than about 0·7 under compression for a fixed and finite value of a / b (i.e. no buckling for long and slender hollow cylinders with small a / L and fixed b / a). When 0·7 〈 γ 〈 0·9, buckling is the expected first bifurcation; whereas, when γ 〉 0·9, bulging or barrelling is anticipated. The exact value of γ that excludes buckling and separates the buckling and barrelling phenomena depends on the current values of the constitutive parameters of the solid. Hollow cylinders with higher degree of anisotropy, disobeying normality flow rule, and subjected to confining pressure are more conducive to bifurcations than cylinders made of materials with isotropy, obeying normality, and subjected to no confining pressure. In addition, diffuse mode bifurcations are found possible in the pre-peak regime of the stress-strain curve. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 983-1000 
    ISSN: 0363-9061
    Keywords: geomechanics ; indirect boundary element method (BEM) ; three-dimensional (3-D) elastostatics ; iterative methods ; approximate solution ; Engineering ; Civil and Mechanical Engineering
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    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The research herein primarily addresses to geomechanical problems of underground constructions in Mining and Civil Engineering. The problems are solved using the Indirect Boundary Element Method (IBEM). Although the geometry of the constructions themselves is usually very complicated, it will become much more complicated if we were to draw the existing joints. The computational problem therefore is how to deal with huge amount of equations and find out efficient methods of their formation and solution keeping in mind restraints of the computer memory and calculation time. Several approaches are used to enhance the performance of the Indirect Boundary Element Method. One of them deals with application of efficient equation solvers. It is shown that Krylov-type methods like CGS and GMRES with simple Jacoby preconditioning appear to be efficient and robust. In addition, adaptive integration on the boundary elements, together with diagonal dominance of equationsmake it possible to accelerate convergence of the iterative procedure. Some of the problems discussed allow a substantial reduction of matrix entries that leads to a very cheap iterative solution keeping reasonable accuracy of the results. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 97-132 
    ISSN: 0363-9061
    Keywords: constitutive model ; rate-independent type ; strain response envelope ; granular material ; uniqueness ; Engineering ; Civil and Mechanical Engineering
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    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper reviews some incrementally non-linear constitutive equations of interpolation type, and proposes a new approach to illustrate the discrepancies between different interpolation models. This approach uses the strain response envelopes, based on experimental data when restricted to triaxial plane, and the Jacobian of the constitutive equations to examine the loss of uniqueness. A new family of interpolation functions is proposed to meet the three requirements: C1-continuity of strain response envelope, correct description of experimental data, and respect of the one-to-one property. © 1998 by John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 153-174 
    ISSN: 0363-9061
    Keywords: finite-element ; sea ice pack ; rheology ; viscous-plastic ; viscous fluid ; Engineering ; Civil and Mechanical Engineering
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    Notes: In this paper the effects of four different rheologies on the evolution of a large-scale sea ice pack are determined and compared. Two rheologies are of viscous-plastic form, and two are viscous fluid relations. The initial pack domain is rectangular, and the motion is driven by wind stress and resisted by ocean drag. Two adjacent edges are rigid shore boundaries, and the other two are free boundaries at open water which move during the pack motion, so that the pack domain changes in time. Two different forms of boundary conditions at the rigid shore edges are considered, which also influence the evolution. The governing equations are solved numerically using a finite-element method, and, unlike previous numerical treatments, no artificial viscosity is incorporated to stabilise the algorithm near interfaces between converging and diverging flow. Instability arises when any tensile stress is abruptly cut-off when diverging flow is initiated, and an alternative view is offered. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 263-275 
    ISSN: 0363-9061
    Keywords: non-ideal interface ; crack scattering ; domain decomposition ; collocation methods ; Engineering ; Civil and Mechanical Engineering
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    Notes: This work presents a numerical algorithm for solving crack scattering in a transversely isotropic medium whose symmetry axis is perpendicular to the crack surface. The crack is modelled as boundary discontinuities in the displacement u and the particle velocity v, of the stresses [κu+ζv], where the brackets denote discontinuities across the interface. The specific stiffness κ introduces frequency-dependence and phase changes in the interface response and the specific viscosity ζ is related to the energy loss.The numerical method is based on a domain decomposition technique that assignes a different mesh to each side of the interface, that includes the crack plane. As stated above, the effects of the crack on wave propagation are modelled through the boundary conditions, that require a special boundary treatment based on characteristic variables. The algorithm solves the particle velocity-stress wave equations and two additional first-order differential equations (two-dimensional case) in the displacement discontinuity. For each mesh, the spatial derivatives normal to the interface are solved by the Chebyshev method, and the spatial derivatives parallel to the interface are computed with the Fourier method. They allow a highly accurate implementation of the boundary conditions and computation of the spatial derivatives, and an optimal discretization of the model space. Moreover, the algorithm allows general material variability. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 327-350 
    ISSN: 0363-9061
    Keywords: finite element analysis ; large strain ; remeshing ; integration ; penetration ; bearing capacity ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A practical method is presented for numerical analysis of problems in solid (in particular soil) mechanics which involve large strains or deformations. The method is similar to what is referred to as ‘arbitrary Lagrangian-Eulerian’, with simple infinitesimal strain incremental analysis combined with regular updating of co-ordinates, remeshing of the domain and interpolation of material and stress parameters. The technique thus differs from the Lagrangian or Eulerian methods more commonly used. Remeshing is accomplished using a fully automatic remeshing technique based on normal offsetting, Delaunay triangulation and Laplacian smoothing. This technique is efficient and robust. It ensures good quality shape and distribution of elements for boundary regions of irregular shape, and is very quick computationally. With remeshing and interpolation, small fluctuations appeared initially in the load-deformation results. In order to minimize these, different increment sizes and remeshing frequencies were explored. Also, various planar linear interpolation techniques were compared, and the unique element method found to work best.Application of the technique is focused on the widespread problem of penetration of surface foundations into soft soil, including deep penetration of foundations where soil flows back over the upper surface of the foundation. Numerical results are presented for a plane strain footing and an axisymmetric jack-up (spudcan) foundation, penetrating deeply into soil which has been modelled as a simple Tresca or Von Mises material, but allowing for increase of the soil strength with depth. The computed results are compared with plasticity solutions for bearing capacity. The numerical method is shown to work extremely well, with potential application to a wide range of soil-structure interaction problems. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 495-508 
    ISSN: 0363-9061
    Keywords: consolidation ; cohesive soil ; clay ; axial strain ; true triaxial ; finite difference method ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper presents a simplified approach for the analysis of axial strain induced by three-dimensional consolidation of cohesive soils. The axial strain is divided into a constant volume component and a consolidation component. A relevant undrained stress-strain relationship is required to determine the constant volume component. A theoretical formulation is developed for the evaluation of the consolidation component. Predictions of the axial strain accompanying true triaxial laboratory tests for a variety of stress patterns correlate sufficiently well with the measured data. The proposed method is potentially applicable in conjunction with a finite difference scheme to analyze the time-dependent response of pile groups subjected to static vertical loading. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 549-574 
    ISSN: 0363-9061
    Keywords: carbonatic clays ; thermo-plasticity ; nuclear waste disposal ; thermo-mechanical tests ; Engineering ; Civil and Mechanical Engineering
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    Notes: Argillaceous masses considered for potential nuclear waste repositories may exhibit significant space variability in their carbonate content. This may affect mechanical clay properties, such as strength or maximum apparent preconsolidation stress known to strongly depend on carbonate content. This paper investigates experimentally the dependence of thermo-hydro-mechanical behaviour of clays on carbonate content. The properties investigated are thermal strains, thermally induced over-consolidation, strength changes, destructuration, and thermally developed water pressure in undrained conditions. The experimental data are analysed in terms of a thermo-elasto-plasticity theory for clays, being an extension of Cam-clay model, modified to include the variability of the carbonatic content. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 695-720 
    ISSN: 0363-9061
    Keywords: wave propagation ; compaction ; pore pressure generation ; Engineering ; Civil and Mechanical Engineering
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    Notes: The propagation of a plane load-unload pulse through a compacting sand is analysed and illustrated for both dry sand and liquid saturated sand in undrained conditions. A major feature is the interaction between the initial loading wave and the faster following unloading wave. Free draining and undrained conditions exhibit distinct qualitative and quantitative results, and the pore liquid pressure generation is a significant physical feature. Illustrations show the effects of different applied surface pulse shapes. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 777-790 
    ISSN: 0363-9061
    Keywords: piles ; rafts ; finite elements ; preconditioning ; conjugate gradients ; Engineering ; Civil and Mechanical Engineering
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    Notes: Analysis of piled raft foundations, taking account of their full three-dimensional complexity, can be accomplished by modern finite element analysis techniques. The characteristics of the (preconditioned conjugate gradient) numerical method applied to this problem are analysed, and then the method isused in a field problem of a raft subjected to very rapidly varying loading patterns. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 791-818 
    ISSN: 0363-9061
    Keywords: Engineering ; Civil and Mechanical Engineering
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    Notes: An analytical model to simulate the penetration of the piezocone penetrometer in cohesive soils is presented here. The elasto-plastic coupled field equations of the saturated cohesive soils (given by Voyiadjis and Abu-Farsakh) is used in this analysis. The numerical simulation of the piezocone penetration is implemented into a finite element program. The analytical model is used to analyze the miniature piezocone penetration tests (PCPT) conducted at LSU calibration chambers. Simulation of the piezocone penetration is done for two cases. In the first case, the soil-penetrometer interface friction is neglected, while in the second case, the soil-penetrometer interface friction is taken into consideration. The constraint approach is used to model the soil-piezocone interface friction in which the Mohr-Coulomb frictional model is used to define the sliding potential. Analysis is done for three different soil specimens with different stress histories. The results of the numerical simulations are compared with the experimental measurements of the miniature piezocone penetration tests (PCPT) in cohesive soil specimens conducted in LSU calibration chambers. The resulting excess pore pressure distribution and its dissipation using the numerical model are compared with some available prediction methods. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 1001-1020 
    ISSN: 0363-9061
    Keywords: stone-column reinforcement ; homogenisation technique ; elastoplastic analysis ; sub-iteration scheme ; Engineering ; Civil and Mechanical Engineering
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    Notes: A numerical model is proposed to analyse elastic as well as elastoplastic behaviour of stone-column reinforced foundations. The stone-columns are assumed to be dispersed within the in situ soil and a homogenization technique is invoked to establish equivalent material properties for in situ soil and stone-column composite. The difficulties encountered in carrying out elastoplastic analyses of composite materials are overcome by adopting a separate yield function for each of the constituent materials and a sub-iteration procedure within an implicit backward Euler stress integration scheme. In the proposed procedure, equilibrium as well as kinematic conditions implied in the homogenization procedure are satisfied for both elastic as well as elastoplastic stress states.The proposed model is implemented in an axi-symmetric finite element code and numerical prediction is made for the behaviour of model circular footings resting on stone-column reinforced foundations. This prediction indicates good agreement with experimental observation. Finally, a new scheme in which the length of stone-column is variable is proposed and its behaviour is examined through a numerical example. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 969-981 
    ISSN: 0363-9061
    Keywords: heat and moisture flow ; analytical solution ; transient analysis ; spherical heat source ; coupled analysis ; Green's function method ; Engineering ; Civil and Mechanical Engineering
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    Notes: The present paper develops an analytical approach to the problem of heat-induced moisture movement in the vicinity of a spherical heat source embedded in an undeformable, moist porous solid of infinite extent. A transient-state distribution of temperature within the infinite medium is assumed to induce the moisture transport process. The numerical results, presented in the paper, illustrate the influence of the moisture transport characteristics on the time-dependent distribution of moisture within the porous medium. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 49-71 
    ISSN: 0363-9061
    Keywords: unsaturated soil ; heat transfer ; moisture transfer and stress-strain behaviour ; model and validation ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: This paper focuses attention on the development of a numerical model of the hydro/thermo/mechanical behaviour of unsaturated clay and its consequent verification and validation. The work presented describes on-going collaboration between the Cardiff School of Engineering and Atomic Energy of Canada. The model development, which was carried out at Cardiff, can be described as being based on a mechanistic approach to coupled heat, moisture and air flow. This is then linked to a deformation analysis of the material within a ‘consolidation’ type of model. The whole is solved via the finite element method to yield a computer software code named COMPASS (COde for Modelling PArtly Saturated Soil). Some aspects of verification and validation of the model have been addressed in-house. However, the purpose of current AECL work is to provide an independent, rigorous, structured programme of validation and the paper will also explore the further validation of COMPASS within this context. © 1998 by John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 133-149 
    ISSN: 0363-9061
    Keywords: thermoporoelasticity ; thermoporoplasticity ; Laplace transform ; Stehfest algorithm ; finite element method ; Engineering ; Civil and Mechanical Engineering
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    Notes: Solutions are presented for the behaviour of a layered porous space which contains a decaying heat source. Such a problem arises when high-level nuclear waste is placed in deep underground depositories in deep clayey formations of sedimentary basins. The geometry of the problem is one dimensional and the porous space is constituted by two layers: a deep low permeability layer which contains the nuclear waste disposal and a superficial layer. The solution is used to examine the effects of contrasts of permeability, thermal conductivity and specific heat capacities between the two layers on the large-scale behaviour of the porous space. Results are presented, using realistic data, for the pore pressure and temperature evolution at the heat source centre, and for the vertical displacement of the ground level. The superficial layer has no significant effects on pore pressure, temperature and stress evolution near the heat source centre. The vertical displacement of the ground level is mainly due to the thermal dilatation of the pore water, so it decreases with an increasing of permeability of the superficial layer. The solution of the time-dependent problem is carried out by applying Laplace transforms to the field variables, obtaining solutions and then using numerical methods to invert the transformed solutions. Comparisons with numerical simulations taking into account the non-linear and non-reversible behaviour of the rock mass are presented. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 245-261 
    ISSN: 0363-9061
    Keywords: Cosserat continuum model ; equivalent continuum medium ; layered rock mass ; finite element method ; non-associative plasticity ; Engineering ; Civil and Mechanical Engineering
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    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Layered rock masses can be modelled either as standard, orthotropic continua if the layer bending can be neglected or as Cosserat continua if the influence of layer bending is essential. This paper presents a finite element smeared joint model based on the Cosserat theory. The layers are assumed to be elastic with equal thickness and equal mechanical properties. All the cosserat parameters are expressed through the elastic properties of layers, layer thickness and joint stiffness. Plastic-slip as well as tensile-opening of layer interface (joint) are accounted for in a manner similar to the conventional non-associative plasticity theory.As an application, the behaviour of an excavation in a layered rock mass is examined. The displacement and stress fields given by smeared joint models based on the Cosserat continuum and the conventional anisotropic continuum approaches are compared with those obtained from the discrete joint model. The conventional anisotropic continuum model is found to break-down completely when the effective shear modulus in the direction parallel to layering is low in comparison to the shear modulus of the intact layer, whereas the Cosserat model is found to be capable of accurately reproducing complex load-deflection patterns irrespective of the differences in shear moduli. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 393-416 
    ISSN: 0363-9061
    Keywords: fabric ; porosity ; tensor ; yield ; stress ; strain ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The porosity of soils is considered to be a directional measure and its distribution is characterized by a functional form. This form has been used to extend the critical state soil mechanics framework to include the effects of structure in soils. A new internal plastic energy dissipation formulation has been proposed to account for fabric arrangement. New expressions for the yield locus, and the plastic stress-strain response of structural soils have been derived. The applicability of the concepts to model the plastic stress-strain behaviour of a number of soils is illustrated. The advantage of the new model is very well identified in modelling the stress-strain behaviour of K0 consolidated and natural clays. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 477-493 
    ISSN: 0363-9061
    Keywords: foundation ; pile ; raft ; analysis ; case history ; Engineering ; Civil and Mechanical Engineering
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    Notes: An approximate numerical method for the analysis of piled raft foundations is presented. The raft is modelled as a thin plate and the piles as interacting non-linear springs. Both the raft and the piles are interacting with the soil which is modelled as an elastic layer. Two sources of non-linearity are accounted for: (i) the unilateral contact at the raft-soil interface and (ii) the non-linear load-settlement relationship of the piles. Both theoretical solutions and experimental results are used to verify that, despite the approximations involved, the proposed method of analysis can provide satisfactory solutions in both linear and non-linear range. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 515-548 
    ISSN: 0363-9061
    Keywords: coupled analysis ; expansive clay ; granite ; radioactive waste ; thermo-hydro-mechanical analysis ; unsaturated soils ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Coupled thermo-hydro-mechanical (THM) analyses have been used to examine the interacting phenomena associated with the simultaneous heating and hydration of an engineered bentonite barrier placed in a drift excavated in granite. The specific problem studied is an in situ test being carried out in the underground laboratory at Grimsel (Switzerland). After describing the test and the theoretical formulation, the results of a coupled THM analysis using the best parameter estimation currently available are presented and discussed. The effect of various features of analysis are explored by means of additional analyses in which each of those features are varied, one at the time. Finally, sensitivity analyses have been carried out to examine some critical aspects of the in situ test design. Performance of coupled THM analyses has led to a better understanding of the various inter-related phenomena occurring during heating and hydration of the engineered clay barrier. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 655-669 
    ISSN: 0363-9061
    Keywords: elastic nonhomogeneity ; soil deformation ; soil stresses ; surface loading ; Engineering ; Civil and Mechanical Engineering
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    Notes: The response of a compressible continuously non-homogeneous elastic soil to a static vertical point load on its surface is analytically investigated by using classical integral transform techniques and the extended power series method for obtaining the solution in the transform domain. The non-homogeneity is described by means of a depth-function which is non-zero at the surface and bounded at infinity and is capable in modelling both increasing and decreasing soil stiffness with depth. The influence of non-homogeneity on the displacements and stresses at the surface and in the interior is examined over a wide range on the governing parameters. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 721-748 
    ISSN: 0363-9061
    Keywords: cyclic behaviour ; saturated sands ; disturbed state concept ; liquefaction ; post liquefaction ; threshold transitions ; laboratory tests ; validations ; mathematical analysis ; computer implementation ; application ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A fundamental procedure is proposed for the identification of liquefaction in saturated soils based on the instability in the material's microstructure. The disturbed state concept (DSC) provides a unified constitutive model for the characterization of entire stress-strain behaviour under cyclic loading, and the values of disturbance at threshold states in the deforming microstructure provides the basis for the identification of liquefaction. The procedure is verified with respect to laboratory behaviour of two sands, saturated Ottawa and Reid Bedford. A mathematical analysis of the DSC constitutive matrix is also performed. Procedures for the application of the DSC for simplified analysis and design, and in finite element procedures are presented. It is believed that the proposed model can provide a fundamental yet simplified procedure for liquefaction analysis, and as a result, it is considered to be an improvement over the available empirical and energy-based procedures. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 819-850 
    ISSN: 0363-9061
    Keywords: stochastic ; finite element ; seismic ; response ; random ; variability ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Some of the available stochastic finite element methods are adapted and evaluated for the analyses of response of soils with uncertain properties subjected to earthquake induced random ground motion. In this study, the dynamic response of a soil mass, with finite element discretization, is formulated in the frequency domain. The spectral density function of the response variables are obtained from which the evaluation of the root-mean-squared and the most probable extreme values of the response are made. The material non-linearities are incorporated by using strain compatible moduli and damping of soils using an equivalent linear model for stress-strain behaviour of soils and an iterative solution of the response. The spatial variability of the shear modulus is described through a random field model and the earthquake included motion is treated as a stochastic process. The available formulations of direct Monte-Carlo simulation, first-order perturbation method, a spectral decomposition method with Neumann expansion and a spectral decomposition method with Polynomial Chaos are used to develop stochastic finite element analyses of the seismic response of soils. The numerical results from these approaches are compared with respect to their accuracy and computational efficiency. © 1998 John Wiley & Sons Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 921-940 
    ISSN: 0363-9061
    Keywords: anisotropic sand ; constitutive model ; non-linear tensorial junctions ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The paper presents a constitutive model for the three-dimensional deformation-strength behaviour of inherently anisotropic sand. Based on non-linear tensorial functions, the model is developed without recourse to the concepts in plasticity theory such as yield surface and plastic potential. Benefited from the fact that no decomposition of strain into elastic and plastic parts is assumed, a unified treatment of anisotropic behaviour of deformation and strength is achieved. Anisotropy is characterized by a vector normal to the bedding plane. The extension of the constitutive model is furnished by incorporating the vector under consideration of the principle of objectivity and the condition of material symmetry. Distinct features of the model are its elegant formulation and its simple structure involving few material parameters. Model performance and comparison with experiments show that the model is capable of capturing the salient behaviour of anisotropic sand. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 947-968 
    ISSN: 0363-9061
    Keywords: boundary element method ; complex hypersingular integrals ; Engineering ; Civil and Mechanical Engineering
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    Notes: The definitions of complex integrals of Cauchy and Hadamard with the singular point coinciding with the end point of the integration curve are proposed. It is shown that the new integrals satisfy most of the properties of the regular ones, including the change of variables. It is also shown that the Cauchy principal value (CPV) and Hadamard finite-part (HFP) integrals can be considered as a sum of the new type integrals. The application to numerical solution by the boundary element method (BEM) and the complex hypersingular integral equation (CHSIE) for the multiregions of interacting elastic bodies and bodies with cracks and holes is discussed. The different ways to place the collocation points are considered. The numerical results for the problems of circular hole and circular elastic inclusion in infinite plate indicated that the appropriate choice of the approximating functions leads to a high accuracy of the calculation. Applications of the new technique to geomechanics problems are discussed. © 1998 John Wiley & Sons, Ltd.
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  • 45
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 73-75 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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  • 46
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 153-154 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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  • 47
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 191-208 
    ISSN: 0363-9061
    Keywords: foundation design ; pavement design ; layer-stiffness technique ; moving strip load ; Engineering ; Engineering General
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    Notes: Analytical determination of stresses and deformations caused by moving loads is vital to foundation and pavement designs. In current applications, moving loads are often approximated to be vertical impact loads. In this work, however, a live load is modelled as a uniform distribution of normal or shear stresses in actual motion. Then, a layer stiffness approach utilizing linear elasticity is followed in determining the surface and interior deformations due to the live load. By superimposing the two solutions for normal and shear surface stresses, the new approach can be made to provide an approximate solution to the problem of evaluating stresses and deformations caused by a wide wheel load rolling on a layered elastic system. Although elastic solutions in general are inadequate to explain the more significant consequences of pore pressure generation and dissipation in the soil subgrade, these results can certainly be useful to examine the shearing effects of wide rolling wheels on the asphalt layer and immediate settlement of the subgrade. It is found that the dynamic effects of a smoothly rolling wide load are significant at relatively low wheel velocities compared to those of shear waves in the subgrade and base.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 143-152 
    ISSN: 0363-9061
    Keywords: settlement ; axially loaded ; circular ; piles ; piers ; drilled shafts ; caissons ; numerical model ; variational principles ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: A variational model for the analysis of axially loaded piers is presented. A closed-form solution technique employing an iterative procedure, is developed to obtain the displacement and forces in the pier along its axial direction. The method is suitable for similar analyses of pile foundations. It is shown that displacements and the load distribution along the axis of the pier compare well with a more sophisticated finite element solution. Furthermore, the new model complements the well-known Reese model employing t-z curves for the analysis of settlement of axially loaded piers. This new formulation using continuum mechanics principles, distributes the work done by the applied load as compressive strain energy in the pier, and as shear strain energy in the soil, as well as, the compressive strain energy in the soil surrounding the pier and at the bottom of the pier.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 77-77 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 173-190 
    ISSN: 0363-9061
    Keywords: stress/stability analysis ; constitutive modelling ; non-linear fault behaviour ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A boundary element model for stress/stability analysis of underground excavations in the vicinity of faults is presented. The boundary element formulation adopts the fictitious stress method for the simulation of excavation boundaries and the displacement discontinuity method for the representation of faults. The numerical model employs the Barton-Bandis non-linear joint model for the modelling of the fault behaviour and linear elastic behaviour for the rock. An incremental-iterative in situ stress relaxation algorithm is implemented for the non-linear analysis of the faults. Both deformation and peak strength models of Barton-Bandis are incorporated for modelling the mechanical behaviour of the fault. The non-linear deformation of fault considers the effects of coupling between shear and normal stresses and displacement, joint closure, joint separation, hardening followed by post-peak or residual behaviour. The peak strength model employs a mobilized non-linear shear strength envelope. The differences between linear and non-linear simulation of the fault models are discussed. A comparison of model predictions with the classical Mohr-Coulomb peak strength model with constant joint stiffness is presented. The numerical model is used for a case study of Canadian hard rock underground mine. The shear and normal displacements along the fault during four mining sequences with backfill simulation are presented and discussed.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 229-230 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 253-273 
    ISSN: 0363-9061
    Keywords: elastic porous media ; wave propagation ; first-order silent boundary technique ; Engineering ; Engineering General
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    Notes: Wave propagation both in one- and in two-dimensional saturated elastic porous media is analysed by means of a two-field finite element model with silent boundaries. An extension of the elastic ‘multidirectional’ transmitting boundary to two-phase media is developed to simulate the silent boundary condition. The theoretical assessment and the numerical formulation of the first-order silent boundary technique is presented in detail. Some examples are used to demonstrate the reliability of the first-order method, especially for problems with plane and axisymmetric waves having various angles of incidence. Finally, the wave propagation along a pile shaft is presented, to simulate a common non-destructive dynamic pile test.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 287-294 
    ISSN: 0363-9061
    Keywords: torsional surface waves ; propagation ; hoterogeneous half-space ; Engineering ; Engineering General
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    Notes: The paper discusses the propagation of torsional surface wave in a homogeneous substratum over a half-space with linearly varying rigidity and density. The study reveals that under assumed conditions, a torsional surface wave propagates in the medium. The velocities of torsional surface waves have been calculated numerically and are presented in a number of graphs. It is also observed that for a stratum over a homogeneous half-space, the velocity of torsional surface waves coincides with that of Love waves. For a non-homogeneous half-space it is observed that the velocity of torsional surface waves is always higher than that of Love waves propagated in a homogeneous layer over a homogeneous half-space. An attempt is also made to assess the possible propagation of torsional surface waves in a half-space with linearly varying rigidity and density, lacking a superficial layer. It is concluded that such a half-space allows two solutions for torsional waves while a homogeneous half-space has one.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 381-401 
    ISSN: 0363-9061
    Keywords: Poroelasticity ; FEM ; borehole ; anisotropy ; rock mechanics ; Engineering ; Engineering General
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    Notes: The finite element equations for non-linear, anisotropic poroelasticity are cast in the form of measurable engineering constants. Two problems of importance to the rock and petroleum industry are analysed by the FEM. First, the classical Mandel's problem with an extension to transversely isotropic case is investigated. Second, the problem of an inclined borehole is explored. In particular, the effect of material anisotropy on stress concentration near the wall with implication to borehole instability is examined in detail.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 489-516 
    ISSN: 0363-9061
    Keywords: cavity expansion ; critical state models ; plasticity ; pile installation ; normally and overconsolidated clays ; Engineering ; Engineering General
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    Notes: Boundary value problems for hardening/softening soils, such as Cam-Clay, usually require the extensive use of finite element methods. Here analytical and semi-analytical solutions for the undrained expansion of cylindrical and spherical cavities in critical state soils are presented. The strain is finite, the initial cavity radius is arbitrary and the procedure applicable to any isotropically hardening materials. In all cases only simple quadratures are involved, and in the case of the original Cam-Clay a complete analytical solution can be found. In addition to providing models of the behaviour of displacement piles and pressuremeters these results also provide valuable benchmark solutions for verifying various numerical methods.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 595-604 
    ISSN: 0363-9061
    Keywords: compressibility ; elastic settlement ; geosynthetic-reinforced soil ; mechanical foundation model ; prestressing ; Engineering ; Engineering General
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    Notes: In the present paper, a new foundation model has been proposed by introducing a stretched rough elastic membrane in the Pasternak shear layer sandwiched between two spring layers which is an extension of Kerr model. Considering the equilibrium of different elements, the equations governing the elastic settlement response of the model are derived. Finite difference scheme has been employed to solve the governing equations. The parametric studies carried out show the effect of several parameters on the elastic settlement response of the model. The proposed model is well suited for idealizing the behavior of geosynthetic-reinforced granular fill - soft soil system besides other applications.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 571-593 
    ISSN: 0363-9061
    Keywords: methane gas ; finite element ; coal mining ; diffusion ; adsorption ; outbursts ; Engineering ; Engineering General
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    Notes: This paper presents the development of a mathematical model for methane gas migration in coal seams. The major focus of this model is the coupling between the gas flow and deformation of solid coal. The effect of diffusion of adsorbed methane gas from the solid matrix to the voids has been taken into account. The adsorption of gas in the coal seam causes a two-phase state of gas flow. The governing equation for the two-phase gas flow is a non-linear partial differential equation with non-linear boundary conditions. A finite element model has been developed for simulation of the distribution of pressure and concentration of methane gas due to gas migration in coal seams.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 673-690 
    ISSN: 0363-9061
    Keywords: tunnel analysis ; new implicit method (NIM) ; Engineering ; Engineering General
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    Notes: Tunnel excavation is a coupled three-dimensional problem dealing with two different structures: lining and rockmass. For a simple application it is useful to develop simplified methods by treating the problem as plane strain.If the problem of tunnel face advance presents an axisymmetric geometry, then we show that the major parameter governing the ground-interface-lining interaction is the convergence of the tunnel U0 at the moment of the lining installation.The ‘New Implicit Method’ (NIM) presented in this paper makes use of principles similar to those of the ‘convergence-confinement’ method, but it provides a better appreciation of the coupled behaviour of rockmass and lining. For independent time constitutive laws (elasticity and plasticity), we point out that the convergence U0 depends not only on the mechanical behaviour of the rockmass and on the distance from the tunnel face, as predicted by the ‘convergence-confinement’ method, but also on the stiffness of the lining previously set.We present the ‘NIM’ for elastic and perfect elastoplastic rockmasses without dilatancy for many criteria. The development of this new method is based on the results of tunnel calculations with an axisymmetric FEM numerical model that takes into account the three-dimensional aspect of the problem.Using this method is simple and its results agree well with the FEM numerical results. Its accuracy is highly satisfactory for a geotechnical study.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 693-713 
    ISSN: 0363-9061
    Keywords: unfrozen layer ; osmotic ; diffusion ; transport ; moisture ; temperature ; optimization ; Engineering ; Engineering General
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    Notes: Two series of freezing column tests with distilled water and municipal solid waste leachate were investigated, using illitic silty clay. Temperature distributions along the freezing column were recorded as a function of distance and time. Unfrozen moisture content and osmotic pressures as a function of temperature were calculated.It was shown that temperature distributions as a function of distance and time were similar in all tests, probably as a result of the limited amount of moisture intake. The amount of moisture intake was directly related to freezing time and temperature gradient in the freezing column. Unfrozen moisture contents, ion concentrations and temperature gradients were identified as the controlling parameters that contributed to the boundary layer transport (BLT) of metal ions in frozen specimens. Na+ concentration profiles were mostly dependent on water movement in the freezing column. The behaviour of Ca2+ and Mg2+ cations was similar to Na+; their concentrations in the soil solution decreased with freezing time due to ion exchange.Temperature, moisture content in an unfrozen boundary layer (UBL), and concentration gradient were taken into consideration in the development of a boundary layer transport model (BLTM). Based on the experimental results and Powell's optimization technique, the diffusivity parameters of various metal ions were calculated. Comparison of experimental and predicted results indicated that the BLTM can predict the migration of metal ions in UBL.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 725-751 
    ISSN: 0363-9061
    Keywords: damage mechanics ; earthquakes ; gravity dam ; damage evolution ; absorbing boundary ; anisotropic behaviour ; Engineering ; Engineering General
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    Notes: In this paper, the seismic response analysis of concrete gravity dams is presented using the concept of Continuum Damage Mechanics. The analysis is performed using the finite element technique and a proper material degradation/damage model. The damage criterion used here is a second order tensor model based on elastic-brittle characterization and on a power function of the principal tensile stress. The methodology employed is shown to be computationally efficient and consistent in its treatment of both damage growth and propagation. Other important features considered in the analysis are: (1) dam-foundation interaction (2) appropriate modelling of joined rock mass using continuum damage mechanics, and (3) proper modelling of unbounded domain of foundation rock. The infinite media representation of the foundation material has been achieved by using doubly asymptotic approximation. The results of the analysis indicate that the seismic response of a damaged concrete dam could be significantly different from that of an undamaged one. In particular, the analysis shows that during a seismic event, the microstructure of a damaged zone can significantly change due to growth and propagation of microcracks.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 831-844 
    ISSN: 0363-9061
    Keywords: double porosity ; consolidation ; fissured material ; coupled problems ; Engineering ; Engineering General
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    Notes: The mathematical base of the double porosity concept, consisting of the continuity and equilibrium equation respectively, is briefly reviewed. A quasi-steady-state transfer function, the so-called leakage term, is used. Important aspects of the developed code, based on the double porosity theory, are presented together with two hypothetical example problems. The resulting trend of the settlements are compared to those from previous work and was found to be significantly different. However, the implications are that the present study exhibits a more realistic prediction for the settlement.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 907-908 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    Notes: No Abstract
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 887-905 
    ISSN: 0363-9061
    Keywords: creep ; modelling ; long-term ; triaxial ; drainage ; marine clay ; Engineering ; Engineering General
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    Notes: A new finite element program is introduced and its predictive capabilities are compared to results from two long-term, drained laboratory creep tests on a deep sea clay. The constitutive behaviour is based on Cam clay critical state plasticity theory with creep and time-dependent hardening. Creep is computed using either Singh-Mitchell's three-dimensional equation or Taylor's secondary compression relationship. The experimental creep data include a triaxial specimen subjected to two deviatoric stress increments and a one-dimensional consolidation specimen subjected to three vertical stress increments. In addition, the pore pressure behaviour following an increase in stress is examined in the triaxial sample. Predictions compare favourably to test data, which provide confidence for applying the chosen constitutive model and numerical formulation to solve seabed-related problems on the continental slope that are of interest to geologists, the oil industry and the navy, among others.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
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    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
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    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 517-544 
    ISSN: 0363-9061
    Keywords: rock reinforcement ; load distribution ; cable bolts ; fully grouted ; Engineering ; Engineering General
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    Notes: Explanation for the widely reported observation that fully grouted reinforcement is more effective in hard rock that behaves as a discontinuum than in soft rock is presented. Analytical solutions are presented for the distribution of displacement and load along an untensioned fully grouted elastic bolt, of specified bond stiffness, which is activated during excavation by either a continuous or discontinuous distribution of rock displacement. The results indicate that significantly higher axial loads are developed for the discontinuous case.Since the mechanics of bond failure depend on the type of bolt and grout used, in the second part of the paper a finite difference formulation is introduced and combined with a non-linear model for the bond behaviour of a cement grouted seven-wire strand cable bolt. The results of a parametric study indicate that, because the bond is frictional and depends on confinement at the borehole wall, for the same profile of rock mass displacement lower loads are developed in soft rock. Furthermore, in soft rock, excavation induced stress changes can cause a dramatic reduction in bond strength, so that, even after significant rock mass displacement, the axial load developed is significantly less than the tensile strength of the cable. A combination of these effects can explain why failures of cable bolted ground involve debonding at the cable-grout interface in soft rock, and why instances of cable rupture are confined to hard, blocky rock masses.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
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    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 647-671 
    ISSN: 0363-9061
    Keywords: tailings ; consolidation ; evaporation ; salinity ; numerical modelling ; Engineering ; Engineering General
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    Notes: Large-strain consolidation theory has been used as the basis of a computer program for dealing with the problem of consolidation of slurried tailings. The work was carried out in the context of the gold-mining industry in Western Australia, where net annual evaporation rates are high (from about 3 to more than 4m/yr). Therefore, a simple, but effective, method of dealing with evaporation has been included in the model. The paper describes the model, and then uses it with some typical problems to illustrate its versatility and to show the complexity of the behaviour which can occur.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 691-692 
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    Keywords: Engineering ; Engineering General
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    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. ii 
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    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 79-99 
    ISSN: 0363-9061
    Keywords: Land displacement ; groundwater pumping ; Galerkin finite element model ; Engineering ; Engineering General
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    Notes: Equations of equilibrium (force balance) and flow in multidimensions were coupled in this paper to describe land displacements due to pressure decline in aquifers. A Galerkin finite element model based on these equations was developed. The saturated/unsaturated behaviour and the isotropic/anisotropic properties of permeability and elasticity were considered when the model was formulated. This model was verified by comparing its simulation results with those of known analytical solutions for simplified cases. The simulation of displacements due to pressure decline in unsaturated media was also performed. Those results demonstrated that the choice of boundary ranges for an aquifer with infinite domain may significantly affect the estimated horizontal and vertical displacements. To obtain a good estimation of land displacements, the boundary ranges should be carefully chosen. The displacements occurring in unconfined aquifers are caused by the drop of the water table and the change in body force in the dewatering zone. Simulation results also indicated that the change in body force should be considered once an unconfined aquifer has been pumped. Otherwise, the horizontal and vertical displacements in unconfined aquifers would be overestimated and underestimated, respectively. The behaviour of land displacements due to pumping was shown to be affected by changes in the total stresses in aquifers.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 57-72 
    ISSN: 0363-9061
    Keywords: piled raft systems ; raft-pile-soil interaction ; finite layer methods ; foundations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: This paper presents a method of analysis for piled raft systems constructed in layered soils. The method presented takes account of the interactions of the raft, piles and soil without the cost of a full three-dimensional rigorous analysis. This is done by the use of finite layer methods for the analysis of the soil and finite element methods for the raft. Examples are provided in the paper for piled rafts constructed on layered soils, and results are presented for bending moments in the raft and loads in the piles.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 1-33 
    ISSN: 0363-9061
    Keywords: interface constitutive model ; deformation behaviour ; spherical asperity interaction ; dual asperity interaction ; shear and dilatancy of joints ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: An interface constitutive model is presented accounting for slip and sliding effects and also for dilatancy phenomena. The microslip effects are described by considering spherical asperity interaction with variation of contact area and generation of progressive or reverse slip zones. The incremental constitutive equations are derived with proper memory rules accounting for generation and annihilation of particular slip zones during the process of variable loading. It is further assumed that sliding of spherical contacts occurs along large asperities whose slope varies due to the wear process. The predicted shear and dilatancy curves are shown to provide close quantitative simulation of available experimental data. The strain ratchetting effect for non-symmetric cyclic loading was exhibited using the asperity wear model. The model presented could be applied to simulate rock joints, masonry, or concrete cracked interfaces, under monotonic and cyclic loading.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 155-171 
    ISSN: 0363-9061
    Keywords: pollutant migration ; solute breakthrough curves ; numerical simulation ; porous media ; Engineering ; Engineering General
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    Notes: The effect of heterogeneity on solute transport in porous media is examined by means of physical experiments and controlled numerical simulations. The special cases of layered, clogged and aggregated porous media are particularly investigated. The breakthrough curves (BTCs) obtained from some sections of the physical models are extremely distorted with extended concentration tails. These tailings are caused by different trajectories of the tracer through fine (millimeter and centimeter) scale spatial heterogeneities. On the other hand, BTCs in sections of the physical models having no heterogeneous nature, showed classical ‘S’-shape.A computer simulation based on an improved capacitance model was used to match the experimental data. The BTCs can be represented adequately by the model. However, it seems necessary to determine the fitting parameters experimentally in order to relate them to actual physical phenomena.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 275-285 
    ISSN: 0363-9061
    Keywords: elasticity ; stress analysis ; inclusion ; interface ; sand ; Engineering ; Engineering General
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    Notes: In this paper, the stress states of a sand particle (or aggregate) with an interface layer in a cement paste (or mortar) subjected to uniaxial compression or tension are studied. This is a dual layer inclusion problem. The general analytical solutions of stresses and deformations are obtained in closed form, and the solutions of several special cases including the sand (or aggregate) treated as rigid body and as a hole as well as when the thickness of the interface layer approaches zero are also given.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 295-302 
    ISSN: 0363-9061
    Keywords: cubic-strain quadrilateral ; predicting collapse-loads ; Engineering ; Engineering General
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    Notes: In this paper, a fourth-order displacement (cubic strain) Serendipity quadrilateral element is presented. The shape functions and integration scheme are introduced, followed by a series of convergence tests, indicating that the element does not have any spurious zero-energy modes, and passes the patch test and single-element tests. Modifications are then made to enable the element's use in effective stress analysis problems. Examples are finally solved using the element and a comparison is made between some computed and closed-form solutions. It is also shown that the cubic strain quadrilateral may be used in conjunction with or as a substitute for the cubic strain triangle when predicting collapse loads for undrained plane or axisymmetric problems in the fully plastic range.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 331-349 
    ISSN: 0363-9061
    Keywords: elasticity ; buried pipes ; surface heading ; soil-structure interaction ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: A method is presented which may be used to compute the displacements, strains and moments (both in-plane and transverse) in buried structures such as pipelines and culverts subjected to longitudinal bending. This type of bending can occur if a surface loading such as a vehicular loading or an embankment loading is applied to the soil above the pipe or culvert.Fourier transforms are used to reduce the three-dimensional problem to one involving only two spatial directions, thereby reducing the data preparation and computation time. Conventional finite element analysis is used to approximate the field quantities in the transformed two-dimensional plane. Two Fourier integral element types have been developed which have many applications in geotechnical engineering.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 443-452 
    ISSN: 0363-9061
    Keywords: heat-fluid-stress diffusion ; Gauss-Legendre ; Laplace transform ; Stehfest method ; Engineering ; Engineering General
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    Notes: Three methods (Gauss-Legendre method, Stehfest method and Laplace transform method) are used to evaluate a solution of a coupled heat-fluid linear diffusion equation. Comparing with the results by Jaeger, the accuracy and efficiency of the Stehfest and Gauss-Legendre methods and the limitations of the truncated solutions obtained by Laplace transformation are discussed. It is concluded that the Stehfest method gives accurate results and is numerically more efficient than the other two methods, particularly for the solutions in early time. Two transformations with u=-ln(x) and u=arctan(xπ/2), where u is the original integral variable, are considered in the Gauss-Legendre method.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 431-442 
    ISSN: 0363-9061
    Keywords: foundations ; rigid pier ; moment carrying capacity ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: Numerical predictions of the immediate moment carrying capacity of a short pier foundation in saturated clay are presented. Three-dimensional finite element analyses are carried out using linear and non-linear programs and using a linear axi-symmetric program.Preliminary investigations are made to determine suitable boundary distances for analysis at full-scale and size of loading increment for non-linear analyses.Predictions of the behaviour of prototype pier and of conventional and centrifuge models of this pier are then made. It is shown that the axi-symmetric program yields significantly higher rotations per unit moment than the linear three-dimensional program and that, using both of these programs, elastic analyses of the conventional and centrifuge models and of the prototype yield very similar results. It is also shown that non-linear analyses of the conventional and centrifuge models yield significantly different moment/rotation relationship in accordance with the behaviour actually observed in the model tests. The relationship obtained for the centrifuge model is shown to differ only slightly from that obtained for the prototype, due to the boundary restrictions in the model, and to be of the same order as the centrifuge test result at working condition but not at ultimate capacity.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 545-546 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. ii 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 865-886 
    ISSN: 0363-9061
    Keywords: finite element method ; large deformation ; cone penetration test ; layered soil ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: An Eulerean large-strain finite element formulation is presented to simulate static soil penetration. The method is an extension of the Updated Lagrangean description to an Eulerean formulation taking into account convection of deformation-history-dependent properties as well as material properties. The strength of the soil is characterized by a non-associated Drucker-Prager criterion which depends on peak and critical friction angles. The model is applied to cone penetration in two-layer systems: (a) clay on sand and (b) sand on clay.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 635-646 
    ISSN: 0363-9061
    Keywords: slope stabilization ; piles ; soil response modelling ; Engineering ; Engineering General
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    Notes: Piles used for the stabilization of slopes have to be adequately designed to resist the induced lateral loads due to the movement of the unstable slope. In this paper, a numerical method is presented for the analysis of this problem. In this approach, the piles are modelled using beam finite elements. The soil response at the individual piles is modelled using the modulus of subgrade reaction and pile-soil-pile interaction considered using the theory of elasticity. Two case histories, one for single pile and the other for pile group, are analysed which show that the numerical model can predict the general characteristics of the piles reasonably well. The study suggests that the design of the piles based on the computed response from single pile analysis, ignoring group effects, may be unduly conservative.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
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    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 753-767 
    ISSN: 0363-9061
    Keywords: dynamic ; compaction ; soil ; damping ; non-linear stressing ; Engineering ; Engineering General
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    Notes: The majority of currently available analytical tools to predict ground stresses due to impact are based on linear spring-dashpot dynamic models. Although these simple models adequately represent stiff ground possessing linear visco-elastic behaviour, they suffer from two striking limitations when applied to relatively softer ground; (1) the inability to account for the permanent deformation resulting from impact, (2) failure to incorporate stiffness changes of softer soil within the impact duration. In this paper, the authors present an improved analytical approach formulated on the basis of a series of laboratory impact tests, to address the shortcomings of the current dynamic models in relation to soft soils. In this procedure, the impact zone is modelled as three distinct zones; (1) a zone beneath the falling weight undergoing non-linear axial deformation while being in vertical motion, (2) an inner zone immediately surrounding zone 1 with non-linear shear deformation, and (3) an outer zone undergoing a relatively lower degree of (linear) shear deformation. The soil constitutive parameters pertinent to the model are obtained from a modified dynamic compression test that simulates the impact conditions. It is shown that analytical predictions of the impact stress history and penetration are in agreement with test results. The findings are useful in the exploration of dynamic compaction techniques that will be effective in soft soil improvement.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
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    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 845-846 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
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    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 231-252 
    ISSN: 0363-9061
    Keywords: interfaces and joints ; landslides ; viscoplastic behavior ; hierarchical single surface models ; laboratory testing ; calibration ; finite element method ; validations ; Engineering ; Engineering General
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    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A constitutive model to describe viscoplastic or time-dependent behaviour of interface materials is presented. Viscoplastic characteristics of the interface material are modeled based on Perzyna's theory of viscoplasticity and the Hierarchical Single Surface (HiSS) series of constitutive models. Experiments performed using a new interface test device to characterize the behaviour of cohesive soil-rock interfaces are described. Procedures to derive model parameters are presented together with validation of the model. Finite element implementation of the interface element is described along with verification of the model with respect to field behaviour of a creeping natural slope.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 365-375 
    ISSN: 0363-9061
    Keywords: Rayleigh waves ; propagation ; heterogeneous incompressible substratum ; homogeneous incompressible half-space ; Engineering ; Engineering General
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    Notes: The paper studies the propagation of Rayleigh waves in an incompressible layer with general variation of rigidity as μ=μ0(1+bz)m resting over a homogeneous incompressible elastic half-space. Instead of using the Whittaker function, the expansion formula proposed by Newlands has been used for better results at shallow depths. As a particular case for m=1, the results have been shown to coincide with those obtained by Newlands. The velocities have been computed for different values of m and the results are presented in graphs.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 351-364 
    ISSN: 0363-9061
    Keywords: elastic non-homogeneity ; circular foundation ; elastic indentation ; integral equations ; weathered crust ; contact problem ; surface non-homogeneity ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The present paper examines the elastostatic problem pertaining to the axisymmetric loading of a rigid circular foundation resting on the surface of a non-homogeneous elastic half-space. The non-homogeneity corresponds to a depth variation in the linear elastic shear modulus according to the exponential form G(z)=G1+G2e-ζz. The equations of elasticity governing this type of non-homogeneity are solved by employing a Hankel transform technique. The mixed boundary value problem associated with the indentation of the half-space by the rigid circular foundation is reduced to a Fredholm integral equation which is solved via a numerical technique. The numerical results presented in the paper illustrate the influence of the near-surface elastic non-homogeneity on the settlement of the foundation.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 403-430 
    ISSN: 0363-9061
    Keywords: swelling ; chemo-poroelasticity ; borehole stability ; osmosis ; Engineering ; Engineering General
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    Notes: Water-absorbing rocks are formed from minerals that can hold water in their crystal structure or between grain boundaries. Such water absorption is often accompanied by a change in the crystal dimension that manifests itself as a swelling of the rock. Swelling is particularly pronounced in rocks containing phyllosilicates because of the ease with which these minerals hydrate; it is thus of geological and geotechnical relevance in shales, clay-rich soils and zeolitized tuffs. The model of hydration swelling that we present here is based on extended versions of the equations of poroelasticity and Darcy's transport law, which we derive using a non-equilibrium thermodynamics approach. Our equations account for the hydration reaction under the assumption that the reaction rate is fast in comparison with the rate at which hydraulic state changes are communicated through the rock, i.e. that local physico-chemical equilibrium persists. Using a finite-element scheme for solving numerically the governing equations of our model, we simulate the creep of shales during a routine swelling test and calculate the stress and strain distributions around wellbores drilled in shale formations that undergo swelling. We show that swelling effects promote tensile failure of the wellbore wall.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 303-304 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    Topics: Architecture, Civil Engineering, Surveying , Geosciences
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
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    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 771-783 
    ISSN: 0363-9061
    Keywords: localization ; regularization ; discontinuity ; plasticity ; mohr-Coulomb ; ductile fracture ; Engineering ; Engineering General
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    Notes: A frictional material model is investigated with respect to the existence and development of a regularized strong discontinuity within the constitutive framework of plasticity theory. It appears that the condition for the existence of such a discontinuity is identical to the classical bifurcation criterion for band shaped bifurcation in the rate of deformation field. The model behaviour is also discussed beyond onset of localization, for a band with fixed orientation, where the state variables are allowed to change.
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