bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of plastic regions around underground openings by a coupled boundary‐element‐characteristics method
Authors: Obara Yuzo , Nakayama Tomoharu , Sugawara Katsuhiko , Aoki Toshiro , Jang Hyun Kuk 
Published: August 2005

AbstractA two‐dimensional hybrid method for solving elastoplastic problems in engineering is presented by coupling two existing methods, namely, the boundary element method and the characteristics method. The formulation of this method is presented, as well as an excellent procedure for the determination of the boundary between elastic and plastic regions. It is shown not only that this method is a powerful and accurate method for evaluating the shape and extent of the plastic region around rock caverns, which is of prime importance for the construction of rock caverns, but also applicable to a given range of the initial stress field ratio where only compressive failure occurs. Then, some typical examples are solved in order to check the accuracy of the solution by this method. Furthermore, its successful applications are presented and discussed to determine the shape and the extent of the plastic regions around parallel, circular and rectangular openings.
Reconstruction of the parameters of plane‐layered elastic media by generalized ray theory
Authors: Jeng Yu‐Shiuh , Chen Pei‐Lin 
Published: August 2005

AbstractThis paper seeks to reconstruct the parameters of elastic layered media such as P‐wave velocity, S‐wave velocity, density and thickness from the multioffset seismic reflection data. Since the data are highly non‐linear to the low‐wavenumber components, the non‐linear waveform inversion method, with the aid of generalized ray theory, is proposed to solve this problem in space–time domain. As opposed to the layer‐stripping method, the present method attempts to invert all layer parameters simultaneously, thus reducing the cumulative errors resulting from the upper layers. The parameters are inverted by minimizing the weighted square error between the observed data and the calculated data of the layered model, the optimization of which is based on the quasi‐Newton method. In synthetic tests, we find that the inverted results are good when the variation of parameters between layers is not too large. The modified method for large variation of parameters is first to fix those of deeper layers and neglect the signals reflected from them, then recover some other parameters simultaneously until those of upper layers attain a stable value, and finally, invert all parameters simultaneously. The results so obtained show a significant improvement. This method was tested to be stable in the presence of noise in seismograms.
Effect of adjoining structures on seismic response of tunnels
Authors: Navarro C. 
Published: August 2005

AbstractIn this paper the seismic behaviour of buried concrete tunnels is studied using the finite element method. The numerical tool employed is the well‐known soil–structure interaction computer program FLUSH and thus analyses are carried out in the frequency domain. The seismic environment is supposed to consist of vertically propagating shear and compression waves that reproduce artificial accelerograms of a broad frequency content at selected control points. The effect of near or adjacent massive structures, such as those of nuclear power plants, is evaluated showing their influence on tunnel response. The results calculated for acceleration levels, internal structural loads, response spectra, etc., are analysed and compared either with those obtained from soil free‐field response or with others computed using an alternative simplified methodology, providing useful information for preliminary design purposes.
Fracture energy release and size effect in borehole breakout
Authors: Bažant Zdeněk P. , Lin Feng‐Bao , Lippmann Horst 
Published: August 2005

AbstractThe paper presents a simple approximate analytical solution of the remote stresses that cause the collapse of a borehole or other circular cylindrical cavity in an infinite elastic space. Regions of parallel equidistant splitting cracks are assumed to form on the sides of the cavity. Their boundary is assumed to be an ellipse of a growing horizontal axis, the other axis remaining equal to the borehole diameter. The slabs of rock between the splitting cracks are assumed to buckle as slender columns, and their post‐critical stress is considered as the residual stress in the cracked rock. The buckling of these slab columns is assumed to be resisted not only by their elastic bending stiffness but also shear stresses produced on rough crack faces by relative shear displacements. The energy release from the infinite medium caused by the growth of the elliptical cracking region is evaluated according to Eschelby's theorem. This release is set equal to the energy dissipated by the formation of all the splitting cracks, which is calculated under the assumption of constant fracture energy. This yields the collapse stress as a function of the elastic moduli, fracture energy, ratio of the remote principal stresses, crack shear resistance characteristic and borehole diameter. The collapse stress as a function of crack spacing is found to have a minimum, and the correct crack spacing is determined from this minimum. For small enough diameters, the crack spacing increases as the (4/5)‐power of the borehole diameter, while for large enough diameters a constant spacing is approached. In contrast to plastic solutions, the breakout stress exhibits a size effect, such that for small enough diameters the breakout stress decreases as the (− 2/5)‐power of the borehole diameter, while for large enough diameters a constant limiting value is approached. Finally, some numerical estimates are given and the validity of various simplifying assumptions made is discussed.
Slope stability analysis for undrained loading conditions
Authors: Baker R. , Frydman S. , Talesnick M. 
Published: August 2005

AbstractThe current state of art for limit equilibrium analysis of slope stability problems lacks a satisfactory procedure for stability evaluation under general, rapid (undrained) loading conditions. Some procedures are available for the analysis of rapid drawdown, but these suffer from several shortcomings and, furthermore, are not applicable to other types of rapid loading. An approach is presented which overcomes these limitations. The approach integrates four components‐establishment of soil behaviour on the basis of laboratory testing, estimation of steady‐state conditions in the slope using a boundary value analysis, estimation of distribution of undrained strength in the slope using undrained stress paths, and identification of the critical slip surface followed by calculation of its factor of safety. The approach is illustrated through its application to the stability analysis of an earth dam under rapid drawdown and earthquake conditions.
Thermomechanical effects on adsorbed water in clays around a heat source
Authors: Ma Chenmin , Hueckel Tomasz 
Published: August 2005

AbstractNumerical results of the simulations of the saturated clay response to a line heat source with a constant power output are presented and compared to the analytical solutions. Mixture theory of two interacting thermoelastic constituents is employed for the modelling. In this theory, mass transfer between the adsorbed water and bulk water is included to simulate the degeneration of adsorbed water into bulk water occurring at elevated temperatures. A finite difference method with non‐uniform mesh is adopted to determine both the near‐ and far‐field behaviour. The degeneration of adsorbed water into bulk water is more pronounced close to the heat source. This may produce a lower excess pore water pressure, a higher permeability increase, and accelerate the water flow in the vicinity of the heat source.
The analysis of pollutant migration through soil with linear hereditary time‐dependent sorption
Authors: Smith David W. , Rowe R. Kerry , Booker John R. 
Published: August 2005

AbstractThis paper presents a non‐equilibrium sorption dispersion–advection transport model for the analysis of pollutant migration through soil. The formulation involves a convolution integral of the product of the rate of change of concentration and a time‐dependent sorption coefficient, suggesting an integral transformation of the governing equations. This facilitates the primary purpose of this paper, to incorporate a time‐dependent solute sorption process into a computationally efficient and accurate semi‐analytic Laplace transform method. An application of the non‐equilibrium sorption model for backfiguring dispersion–advection equation parameters from experimental data is presented, and the implications of non‐equilibrium sorption on the design of landfill liners is explored by means of an illustrative example.
A Godunov method for localization in elastoplastic granular flow
Authors: Pitman E. Bruce 
Published: August 2005

AbstractThe equations governing the elastic‐plastic deformation of granular materials are typically hyperbolic, or contain small‐magnitude damping or rate effects. A finite element algorithm is the standard method for the numerical integration of these systems. In particular, finite elements allow great flexibility in the design of grid geometry. However, modern finite difference methods for hyperbolic systems have been successful in aerodynamics computations, resolving wave structures more sharply than finite element schemes. In this paper we develop a finite difference scheme for granular flow problems. We report on a second‐order Godunov‐type scheme for the integration of hyperbolic equations for the elastoplastic deformation of a simple model of granular flow. The Godunov method includes a characteristic tracing step in the integration, providing minimal wave dispersion, and a slope limiting step, preventing unphysical oscillations.The granular flow model we consider is hyperbolic, but hyperbolicity is lost at a large value of accumulated plastic strain. This loss of hyperbolicity is a tell‐tale signal for the formation of a shear band within the sample. Typically, when systems lose hyperbolicity a regularization mechanism is added to the model equations in order to maintain the well posedness of the system. These regularizations include viscosity, viscoplasticity, higher‐order gradient effects or stress coupling. Here we appeal to a very different kind of regularization. When the system loses hyperbolicity and a shear band forms, we treat the band as an internal boundary, and impose jump conditions at this boundary. Away from the band, the system remains hyperbolic and the integration step proceeds as usual.
Finite element modelling of rock‐socketed piles
Authors: Leong E. C. , Randolph M. F. 
Published: August 2005

AbstractRock socketed piles have a number of features which differentiate them from other types of piles. The generally stubby geometry leads to more even distribution of capacity between shaft and base. However, the low ratio of pile modulus to rock modulus leads to high compressibility and this, coupled with a tendency for the load transfer response along the shaft to exhibit strain‐softening, gives rise to an overall response where the shaft capacity may be fully mobilized, and potentially degraded, before significant mobilization of base load.The paper presents results of finite element analyses of the response of rock‐socketed piles, with particular attention to the shaft response with and without intimate base contact. The shaft interface uses a model, developed from principles of tribology, that includes dilation (and strain‐hardening) prior to peak shaft friction, followed by strain‐softening at larger displacements. The results of the study are shown to be consistent with field measurements, and to capture effects of the absolute pile diameter on the peak shaft friction. It is also shown that intimate base contact mitigates significantly the degree of strain‐softening of the shaft response.
A 2D coupled finite element and boundary element scheme to simulate the elastic behaviour of jointed rocks
Authors: Carter J. P. , Xiao B. 
Published: August 2005

AbstractIn this paper a coupled finite and boundary element formulation is developed for the analysis of excavation in jointed rock. The presence of joints in the rock mass has been included implicitly by treating it as an appropriate anisotropic elastic continuum. The boundary element formulation for an anisotropic medium is briefly discussed. Good agreement has been found between numerical and analytical solutions for several example problems, demonstrating the accuracy of the present formulation. Numerical solutions are also presented for the problems of a deep circular tunnel and a basement excavated in a variety of jointed rock masses.
On the indentation of a poroelastic layer
Authors: Selvadurai A. P. S. , Yue Z. Q. 
Published: August 2005

AbstractThe paper examines the axisymmetric contact problem related to the indentation of a fluid saturated poroelastic layer by a smooth rigid punch. The layer rests in bonded contact with a rigid impermeable base and the surface of the layer is considered to be either permeable or impermeable. The paper develops the integral equations governing the problem for the generalized case where the pore fluid exhibits compressibility. The numerical results presented in the paper illustrate the influence of the relative layer thickness, drainage conditions and the compressibility of the pore fluid on the degree of consolidation settlement of the indenting punch.
A semi‐analytical method for the wave‐induced seabed response
Authors: Rahman M. S. , El‐Zahaby Khalid , Booker John 
Published: August 2005

AbstractA general semi‐analytical method is presented for the analysis of seabed response under wave action during a storm. The seabed is idealized as a poro‐elastic medium filled with a single compressible fluid with anisotropic flow. The coupled process of fluid flow and deformation of soil skeleton is formulated in the framework of Biot's theory.The analysis for the response of homogeneous seabed of finite thickness under a plane progressive wave is developed first, followed by an extension for the case of a layered seabed. A generalization for three‐dimensional response of seabed is also developed for a general wave field which provides the analyses for seabed response under short‐crested or standing waves in the vicinity of a structure. Some numerical examples illustrating the proposed analyses are also presented.
Finite layer analysis of the behaviour of a raft on a consolidating soil
Authors: Small J. C. , Zhang B. Q. 
Published: August 2005

AbstractA numerical method is developed in this paper for the analysis of the behaviour of a raft resting on a consolidating soil. The response of the raft under an applied loading is determined using the finite layer method for the soil and the finite element method for the raft. By considering deflection compatibility on the contact surface, the distribution of contact pressure is computed at various time steps. The settlement and bending moment in the raft is then evaluated by applying the calculated contact pressure back to the raft. It is shown that, in some cases, the maximum moment in the raft occurs during consolidation and that checking the final moment in the raft by use of elastic theory may not be sufficient.
CLoE, a new rate‐type constitutive model for geomaterials theoretical basis and implementation
Authors: Chambon René , Desrues Jacques , Hammad Walid , Charlier Robert 
Published: August 2005

AbstractThe paper describes the basic ideas and the main features of a new class of constitutive laws, in the framework of incrementally non‐linear constitutive equations. CLoE is a generic name for that new class of laws, with reference to consistency at the limit surface, and explicit localization analysis. A top–down analysis of the model is presented, and illustrated by examples.
Dual‐porosity behaviour of naturally fractured reservoirs
Authors: Bai M. , Ma Q. , Roegiers J.‐C. 
Published: August 2005

AbstractA dual‐porosity model based on the modified formulation by Barenblatt et al. has been presented for the simulation of naturally fractured reservoirs. It is shown that neglecting terms in the flow governing equations may not be justified for some particular physical circumstances. The analytical solution of the proposed dual‐porosity model for a finite naturally fractured reservoir subjected to a constant outer boundary pressure is obtained using the Hankel transform technique while taking into account the transient flow in the matrix blocks. Both solution accuracy and efficiency are achieved utilizing an optimized algorithm when solving the inherent Bessel functions. This research indicates that the transient fluid pressure profiles in naturally fractured reservoirs are critically controlled by the permeability ratio between matrix and fractures, and by the compressibilities of fluid, fractures and solid grains. The fluid pressure change is substantially delayed if the permeability ratio becomes increasingly smaller. The dual‐porosity behaviour is most obvious when the compressibility of the fractures decreases relative to the increases of compressibility of the solid grains.
Monica—A computer algorithm for solving boundary value problems using the double‐hardening constitutive law Monot: I. Algorithm development
Authors: Hicks M. A. 
Published: August 2005

AbstractThe principal features involved in the implementation of the double‐hardening constitutive law Monot1 into a general purpose computer algorithm called MONICA2,3 are described. These include details of general program structure and of steps taken to overcome problems such as computer storage, computer run‐time, algorithm stability and problems associated with the stress–strain singularity which exists at the intersection of the two yield surfaces.
Uncoupling of coupled flows in soil—a finite element method
Authors: Sheng Daichao , Axelsson Kennet 
Published: August 2005

AbstractCoupled flow of water, chemicals, heat and electrical potential in soil are of significance in a variety of circumstances. The problem is characterized by the coupling between different flows, i.e. a flow of one type driven by gradients of other types, and by the dual nature of certain flows, i.e. combined convection and conduction. Effective numerical solutions to the problem are challenged due to the coupling and the dual nature.In this paper, we first present a general expression that can be used to represent various types of coupled flows in soil. A finite element method is then proposed to solve the generalized coupled flows of convection‐conduction pattern. The unknown vector is first decomposed into two parts, a convective part forming a hyperbolic system and a conductive part forming a parabolic system. At each time step, the hyperbolic system is solved analytically to give an initial solution. To solve the multi‐dimensional hyperbolic system, we assume that a common eigenspace exists for the coefficient matrices, so that the system can be uncoupled by transforming the unknown vector to the common eigenspace. The uncoupled system is solved by the method of characteristics. Using the solution of the hyperbolic system as the initial condition, we then solve the parabolic system by a Galerkin finite element method for space discretization and a finite difference scheme for time stepping.The proposed technique can be used for solving multi‐dimensional, transient, coupled or simultaneous flows of convection‐conduction type. Application to a flow example shows that the technique indeed exhibits optimality in convergence and in stability.
On the mechanical response of saturated cemented materials—part I: Theoretical considerations
Authors: Pietruszczak S. , Pande G. N. 
Published: August 2005

AbstractTerzaghi's ‘effective stress’ principle, though originally developed for soils, has been extensively applied to water saturated cemented materials (such as concrete, rocks, masonry units, etc.). There are, however, serious reservations regarding its validity for this class of materials. In this paper an alternative stress decomposition is proposed. It is based on average stress measures in constitutents, i.e. the solid matrix and water. Constitutive relations governing the undrained response of a cemented aggregate mixture, treated as a brittle‐plastic material, are derived. The framework is illustrated by some numerical examples pertaining to the behaviour of saturated concrete.
On the mechanical response of saturated cemented materials—part II: Experimental investigation and numerical simulations
Authors: Pietruszczak S. , Turu G. , Pande G. N. 
Published: August 2005

AbstractResults of experimental investigation and numerical simulations of the mechanical response of the saturated cemented materials are reported. Saturated as well as dry samples cored from commercially available fire bricks are used. The samples were tested in a triaxial rock cell at different initial confining pressures. The tests have been simulated using the constitutive framework proposed in Part I of this paper. The results both experimental and numerical, provide the evidence in support of the proposed stress decomposition, thereby questioning the validity of Terzaghi's principle for the considered class of materials.
Multicontrast MRI of remyelination in the central nervous system
Authors: Merkler Doron , Boretius Susann , Stadelmann Christine , Ernsting Tristan , Michaelis Thomas , Frahm Jens , Brück Wolfgang 
Published: August 2005

AbstractAlthough magnetic resonance imaging (MRI) represents the most sensitive tool for the detection of white matter abnormalities in patients with multiple sclerosis (MS), the heterogeneity of MS placques severely hampers the elucidation of specific pathophysiological processes. In order to identify putative MRI markers for de‐ and remyelination, we employed the cuprizone mouse model which leads to a selective and reversible demyelination of the corpus callosum with little or no axonal damage. Apart from histopathology, animals were studied with high‐resolution three‐dimensional MRI in vivo using multiple contrasts. While individual MRI findings significantly correlated with electron microscopy, the differentiation of regions with normal, demyelinated or remyelinated white matter by one contrast alone was less specific than by histology or electron microscopy. However, an accurate MRI prediction of the in vivo myelin status was achieved by a discriminant function analysis using a combination of T1, T2 and magnetization transfer contrast. With a correct assignment of 95% of all animals examined, the procedure will allow for the survey of new therapeutic approaches aiming at improved remyelination. Copyright © 2005 John Wiley & Sons, Ltd.
Time integration for spherical acoustic finite–infinite element models
Authors: Coyette Jean‐Pierre , Meerbergen Karl , Robbé Mickaël 
Published: August 2005

AbstractIn this paper, we analyse the numerical time integration of models of exterior acoustics. The major challenge lies in the instabilities that may arise from the infinite elements. In this paper we consider the special case of spherical infinite elements formulations, which have shown their relevance for industrial applications. We propose a method that combines Crank–Nicholson's method with a filtering step by the backward Euler method. The paper is illustrated with an example relevant to industry. Copyright © 2005 John Wiley & Sons, Ltd.
Basis of finite element methods for solid continua
Authors: Pian Theodore H. H. , Tong Pin 
Published: August 2005

AbstractFinite element methods can be formulated from the variational principles in solid mechanics by relaxing the continuity requirements along the interelement boundaries. The combination of different variational principles and different boundary continuity conditions yields numerous types of approximate methods. This paper reviews and reinterprets the existing finite element methods and indicates other alternative schemes. Plate bending problems are used to compare the relative merits of the various methods.