bluuebunny/crossref_metadata_2025_split huggingface dataset:
Limit analysis slope stability with nonlinear yield condition
Authors: Drescher A. , Christopoulos C. 
Published: August 2005

AbstractKinematic approach of limit analysis is applied to stability of an infinite, homogeneous, free‐of‐surcharge slope of soil with a nonlinear Mohr–Coulomb yield condition. On operating with a linear yield condition that exceeds the actual nonlinear condition, upper bounds to stability factors are constructed. The solutions overestimate by less than 1% the stability factors given by Zhang and Chen1 for a nonlinear condition.
Bifurcation analysis of deep boreholes: I. Surface instabilities
Authors: Vardoulakis I. G. , Papanastasiou P. C. 
Published: August 2005

AbstractIn this paper a bifurcation analysis of boreholes in deep rock formations under uniform stress at infinity is presented. Rock is described by the constitutive equations of a deformation theory of plasticity for rigidplastic, incompressible and cohesive‐frictional material. The corresponding bifurcation problem is solved numerically by the finite element method. The evidence gained from the numerical solution is utilized to establish a simplified borehole stability analysis that combines Biot's hodograph method with a surface instability analysis.
The interaction between a circular elastic plate and a transversely isotropic elastic half‐space
Authors: Rajapakse R. K. N. D. 
Published: August 2005

AbstractThe axisymmetric problem of flexure of a centrally loaded or uniformly loaded thin‐elastic plate resting on or buried in a transversely isotropic elastic half‐space is solved using a constraint variational scheme. A fundamental solution corresponding to a unit vertical pressure acting over an annular region in the interior of the half‐space which is derived through the application of Hankel integral transforms is used to evaluate the strain energy of the elastic half‐space. The deflected shape of the plate is represented by a power series of radial coordinate together with a term corresponding to a concentrated load derived from classical plate theory. The coefficients of the power series representation, which could be considered as generalized coordinates corresponding to the interaction problem, are determined through the minimization of a constraint energy functional. The energy functional consists of the strain energies of the plate and half‐space, the potential of the applied loads and a term corresponding to plate edge boundary conditions incorporated with a penalty number. The entire formulation is developed as a convenient and flexible matrix solution scheme. The numerical stability and convergence of the solution scheme are established, and the response of the plate is investigated over a range of relative rigidities of practical interest.
Numerical fixed domain mapping solution of free‐surface flows coupled with an evolving interior field
Authors: Hindmarsh Richard C. A. , Hutter Kolumban 
Published: August 2005

AbstractThe evolution of a gravity‐driven free‐surface flow of varying horizontal extent which couples with a field evolving within the flow is solved using a finite difference discretization of a mapping of the problem onto the unit square. Since the size of the solution domain may show several orders of magnitude of variation, while the normalized geometry of the domain and the internal field may not vary significantly, this procedure avoids excessively fine or coarse discretizations, as well as interpolations at the boundary.The parabolic and hyperbolic evolution equations for the internal field are considered. The evolution of the coupled system is solved by an implicit marching scheme. The discretizations in space and in time are accurate to second order. Multipoint upwinding is used to avoid an instability arising advective terms are large.The evolution equations are nonlinear, and are solved using a nested Newton–Raphson procedure. The nesting is achieved by using successively better approximations to the ture evolution equations. The matrix equation that arises is solved by a conjugate‐gradient‐like (ORTHOMIN) iteration procedure with an incomplete Cholesky factorization preconditioning.The method has a wide variety of potential applications in the earth sciences, with the ability to describe glacier flow, lava flow, avalanching and landslides. Some calculations of the thermomechanical evolution of ice‐sheets are given as illustrations, and the possible existence of thermally induced instabilities is considered.
Similarity solutions for wedge‐shaped hydraulic fractures driven into a permeable medium by a constant inlet pressure
Authors: Nilson R. H. 
Published: August 2005

AbstractSimilarity solutions are derived for wedge‐shaped hydraulic fractures driven by a constant inlet pressure P0 into a permeable medium under a uniform confining stress σ. These results describe the seepage‐dominated regime in which most of the injected fluid is lost into the permeable walls of the fracture; they complement previous results for the capacitance‐dominated regime in which seepage is negligible. Fracture propagation velocity is obtained as an analytical function of fracture length, driving pressure, confining stress, material properties and a single separation constant or eigenvalue which is determined numerically. Self‐similar profiles of pressure, opening displacement and fluid velocity along the fracture are presented, together with the self‐similar isobars of the two‐dimensional pressure field within the permeable medium. Comprehensive results are reported for laminar or turbulent flow of a constant‐compressibility liquid or an ideal gas driven by overpressures (P0−σ)/σ ranging from 10−2 to 102.
The properties of anisotropic conical failure surfaces in relation to the Mohr–Coulomb criterion
Authors: Griffiths D. V. , Prevost J. H. 
Published: August 2005

AbstractAn earlier publication1 considered the properties of circular conical failure surfaces whose axes coincide with the space diagonal in principal stress space. The present work uses a similar approach to analyse conical surfaces that are offset from the space diagonal. It is shown that cones fitted to the Mohr–Coulomb surface in triaxial compression contain a potential singularity. The occurrence and location of the singularity depends on the Mohr–Coulomb friction angle to which the surface is fitted in triaxial extension. It is shown that for a cone fitted to the same friction angle in both triaxial extension and compression, singular conditions occur when that angle reaches \documentclass{article}\pagestyle{empty}\begin{document}$ \sin ^{ - 1} \left({\sqrt 7 - 2} \right)\left({ = 40.22^\circ } \right) $\end{document}. Even cones fitted to smaller friction angles give significant overestimations of material strength for certain stress paths.
A direct boundary element method for plane strain poroelasticity
Authors: Cheng Alexander H.‐D. , Detournay Emmanuel 
Published: August 2005

AbstractThis paper presents a direct boundary element method (BEM), formulated in the Laplace transform space, for plane strain poroelasticity. The paper expands on work by Cheng and Liggett by recasting the theoretical foundation of BEM within the framework of Rice and Cleary's formulation of the Biot theory of poroelasticity. Furthermore, the numerical algorithm is generalized to deal with both interior and exterior domain problems, and a method for indirectly calculating the Cauchy principal value of the singular integrals is presented. Formulae for the stress and flux inside the domain are also derived. Finally, the algorithm is validated by comparing the numerical results with the analytical solution of a borehole subject to a far‐field deviatoric stress (exterior domain) and with the solution of Mandel's problem (interior domain). These two examples provide a critical test of the algorithm.
Evaluating the design of an earth dam by finite element analysis
Authors: De Wet M. , Hugo F. 
Published: August 2005

AbstractAn earth dam was to be constructed on a site which posed non‐uniform foundation conditions. The most prominent feature was a vertical contact between unweathered quartzite and decomposed diabase running parallel to the valley. The paper describes a two‐dimensional finite element analysis on the foundation and embankment to determine relative settlements and the possibility of hydraulic fracturing of the clay core. The analysis was extended to evaluate the effectiveness of site improvement measures such as excavation and recompaction of the decomposed diabase and elimination of the contact problem by blasting into the unweathered quartzite. Comparing results from the various analyses, it was concluded that the latter was the only viable solution to the problem.
A model for the ductile yield of porous rock
Authors: Brown E. T. , Yu H. S. 
Published: August 2005

AbstractA relatively simple yield model is developed for isotropic, porous rocks which yield in a ductile manner. The flow rule and yield function are derived using an adaptation of the work‐balance approach of critical state soil mechanics. This adaptation allows for the dissipation of work by frictional and volume change mechanisms, including the dissipation of frictional work at sensibly constant plastic volumetric strain. The yield model uses two material parameters—a basic frictional parameter and a plastic volumetric strain adjustment parameter which is assumed to be constant for the yield locus corresponding to a particular specific volume. The model gives excellent fits to yield loci for two limestones, a chalk and gypsum plaster prepared at different initial void ratios.
On Cryer's problem with large displacements
Authors: Gibson R. E. , Gobert A. , Schiffman R. L. 
Published: August 2005

AbstractThe consolidation of a porous saturated sphere under an isotropic pressure, and free to drain on its surface, is examined. It is shown that a Mandel—Cryer effect develops irrespective of the magnitude of the strains which occur. Surprisingly, the effect is found to be virtually independent of strain. However, the progress of consolidation is substantially faster in the presence of large strains.
Boundary integral analysis of transient thermoelasticity
Authors: Smith D. W. , Booker J. R. 
Published: August 2005

AbstractA simple and efficient method for the solution of uncoupled transient thermoelastic problems using boundary integral techniques is presented. The method employs a Laplace transformation to remove temporarily the time dependence of the governing equations. Numerical analysis is then carried out in the transform space, and results in the time‐position space are found by numerical inversion of the Laplace transform. The method has the advantage that it avoids time‐stepping and the costly evaluation of domain integrals. Boundary element and analytic solutions are compared, and the effect of cooling on the stresses around a deep underground opening is examined.
The effect of Poisson's ratio and the far‐field boundary conditions on the accuracy of finite element calculations
Authors: Fama M. E. Duncan 
Published: August 2005

AbstractIt is shown that a finite element calculation which approximates an ‘infinite medium’; problem by a mesh with finite boundaries will yield greater accuracy when stress boundary conditions are applied on the far‐field boundary than is obtainable with displacement boundary conditions. In particular, with Poisson's ratio close to 0.5, the accuracy of the latter model is severely impaired, whereas the stress boundary condition model is unaffected for Poisson's ratio of 0.49 and a reasonable mesh. The eight‐node quadratic isoparametric element displays superb accuracy for the axisymmetric thick cylinder with either type of boundary condition.
Seismic earth thrust against massive building walls
Authors: Navarro C. , Samartín A. 
Published: August 2005

AbstractThe problem of earth thrust for a massive building in a seismic environment is analysed. Intertial and kinematic soil‐structure interactions are considered by modelling the soil and the structure together. The problem is solved in the frequency domain by using the computer code FLUSH. Results show that the horizontal component of the seismic earth thrust is much greater than that obtained when applying the Mononobe‐Okabe theory. This study establishes a set of conclusicns and recommendations for both design and practical purposes, and proposes future lines of investigation.
Generalization of two‐dimensional discontinuous deformation analysis for forward modelling
Authors: Shi Gen‐hua , Goodman Richard E. 
Published: August 2005

AbstractThis paper provides the theoretical basis for a forward numerical model of rock block systems. This method was developed to compute stress, strain, sliding and opening of rock blocks; rigid body movement and deformation occur simultaneously. Input data consist of block geometry, loading forces, the deformability constants E and v, and the restraint or boundary conditions of the block system. Output data give the movements, deformations, stresses and strains of each block, and the sliding and detachment or rejoining of blocks.The forces acting on each block, from external loading or contact with other blocks, satisfy the equilibrium equations. Equilibrium is also achieved between external forces and the block stresses. Furthermore, this analysis fulfills constraints of no tension between blocks and no penetration of one block into another. To acheive equilibrium and satisfy these constraints, simultaneous equations are solved repeatdly with partial changes of the coefficients each time the contact constraints are chosen.
Kinematic (or hour‐glass) mode control for a uniform strain quadrilateral by an assumed strain technique
Authors: Last N. C. , Harkness R. M. 
Published: August 2005

AbstractFinite element and finite difference solid mechanics computer programs have often been observed to overestimate the stiffness of an elastic beam or the collapse load in elasto‐plastic problems. There are a number of ways of overcoming these difficulties but many lead to unwanted degrees of freedom in the mesh which continuously degrade the solution if the errors are allowed to accumulate. These unwanted distortions are referred to as spurious or hour‐glass modes, and special measures have to be taken if accurate predictions are to be achieved without their appearance. In this paper a new scheme based on assumed strains at the element level is described in the context of a two‐dimensional, explicit, finite difference program. The scheme is compared with an earlier solution to this problem and is shown to have some advantages, particularly when irregular meshes and/or large deformations are encountered. Thorough testing indicates that the new formulation passes the patch test and leads to accurate predictions of bending stiffnesses and plastic collapse loads.An underlying consideration of the development was that the new scheme should be applicable to three‐dimensional calculations. Although this has not been tested numerically, the extension to three dimensions is discussed.
Free convection along a vertical wall in a porous medium with periodic permeability variation
Authors: Singh P. , Misra J. K. , Narayan K. A. 
Published: August 2005

AbstractThis communication investigates the effect of permeability variation on free convection flow and heat transfer in a porous medium bounded by a vertical porous wall. A transverse periodic variation in permeability is considered to study the effect on heat transfer rate and skin friction. The problem becomes three‐dimensional due to the variation in permeability. Analytical expressions for velocity, temperature, skin friction and rate of heat transfer are obtained using the perturbation technique. Effects of permeability and suction parameters on skin friction and heat transfer is studied and it is found that the increase in permeability creates a higher heat transfer rate and greater skin friction. However, the increase in suction parameter causes the skin friction values to decrease. The results obtained will be useful in the design of steam displacement processes in oil recovery and various geothermal systems.
Elastic—plastic response of a circular hole to repeated loading
Authors: Senseny P. E. , Lindberg H. E. , Schwer L. E. 
Published: August 2005

AbstractA closed‐form analysis for elastic—plastic response of a circular hole in an infinite Mohr—Coulomb medium under axisymmetric loading shows the effect of repeated loading on the stress and displacement fields around the hole. Examples show how repeat‐load closure increment is affected by working load, internal pressure, material compressive strength and internal friction. The solution is used to predict results of a laboratory test performed on a rock simulant specimen that contained a reinforced hole. Analytical and laboratory results are similar: at small closures (a few per cent, but well into the plastic response range), the closure increment from an unload—reload cycle is small compared with the initial closure. Closure increments for each of several cycles are comparable and cumulative.
Pore pressure predictions in finite element analysis
Authors: Pacheco M. P. , Altschaeffl A. G. , Chameau J.‐L. 
Published: August 2005

AbstractMany of the existing pore pressure models for FEM analysis are limited either to cases where the pore pressure component produced by the shearing stress is neglected (usually restricted to static analysis) or where the component produced by the mean confining stress is disregarded (usually restricted to cyclic loading, as in earthquake and offshore engineering). A pore pressure model including the simultaneous effects of shear and mean confining stresses is presented in this paper. The model is simple and applicable to static as well as cyclic loading. The conceptual relationship between strains and pore pressure is well recognized in soil mechanics; however, it is difficult to determine the strains by FEM with the necessary accuracy to ensure satisfactory pore pressure predictions, mainly in the range of strains where the concepts of stress path are best applicable. To overcome this limitation, the proposed technique introduces a pore pressure function, to be coupled to a potential and a loading function in an elastic—plastic constitutive model. For simplicity, it is assumed that the pore pressure response can be satisfactorily represented by a path dependent calibrating function determined to fit experiments over a given range of confining pressures. This procedure allows the independent determination of the pore pressure increment before the iterative elastic—plastic procedure is activated, thus supplying the constitutive model directly with the appropriate direction and magnitude of the effective stress increment. The advantages of this procedure during undrained loading are presented in the text.
Variational principles and finite element method for stress analysis of porous media
Authors: Huang N. C. , Szewczyk A. A. , Li Y. C. 
Published: August 2005

AbstractA number of variational principles are established in this paper for the stress analysis of porous media with compressible constituents. A three‐dimensional finite element method is proposed based on the variational principle. The finite element method thus established is applied to the study of the temperature, deformation and flow field associated with the water‐flood technique in secondary recovery projects for oil exploration. In the study model, the layout of injection wells and production wells is considered to have a regular pattern where symmetry conditions exist. The injection fluid diffuses slowly into the formation through a vertical crack which is initially generated by an explosion. The problem is analysed by a plane strain formulation with the effects of heat conduction and convection included.
A numerical procedure for simulation of hydraulically‐driven fracture propagation in poroelastic media
Authors: Boone Thomas J. , Ingraffea Anthony R. 
Published: August 2005

AbstractA procedure for numerical approximation to two‐dimensional, hydraulically‐driven fracture propagation in a poroelastic material is described. The method uses a partitioned solution procedurè to solve a finite element approximation to problems described by the theory of poroelasticity, in conjunction with a finite difference approximation for modelling fluid flow along the fracture. An equilibrium fracture model based on a generalized, Dugdale–Barenblatt concept is used to determine the fracture dimensions. An important feature is that the fracture length is a natural product of the solution algorithm. Two example problems verify the accuracy of the numerical procedure and a third example illustrates a fully‐coupled simulation of fracture propagation. Photographs taken from a high‐performance engineering workstation provide insight into the nature of the coupling among the physical phenomena.
Negative skin friction on pile groups
Authors: Chow Y. K. , Chin J. T. , Lee S. L. 
Published: August 2005

AbstractA numerical procedure is presented for the downdrag analysis of group piles which penetrate a consolidating upper soil layer to socket into a firm bearing stratum of finite stiffness. The settlement of the consolidating upper soil layer under a surcharge load is estimated using Terzaghi's one‐dimensional consolidation theory. Parametric solutions are presented to show the influence of various parameters on the performance of the socketed pile groups in terms of the development of the induced downdrag forces and associated pile head settlements. In general, pile–soil–pile interaction has the beneficial effect of reducing the downdrag forces and settlements of the group piles when compared to the corresponding single pile values, provided that the soil settlements are not so large as to cause full slippage at the interface in all the piles. Reasonable agreement is obtained between the theoretical and experimental results for pile groups subjected to negative skin friction.
Finite element analysis of transient strain localization phenomena in frictional solids
Authors: Leroy Y. , Ortiz M. 
Published: August 2005

AbstractFinite elements with embedded shocks are used to investigate transient strain localization phenomena in frictional solids. In particular, we seek to elucidate the effect of rate sensitivity and inertia on the development of shear bands in solids subjected to impulsive loading. As in the static case, our results show that shear banding may induce severe softening of the specimen even as the material steadily hardens. As expected, rate sensitivity retards the onset of structural softening and tends to stabilize the post‐peak response. It is verified that the static solution is indeed recovered in the inviscid limit. Under dynamic conditions, shear bands are observed to propagate discontinuously, arresting and resuming propagation repeatedly before linking up with the boundary of the specimen. The direction of the band is equally unsteady. In addition, multiple shear banding, with the development of secondary and even tertiary bands, appears to be a prevalent mechanism at sufficiently high impact velocities.
Assessment of using borehole‐closure data to determine the constitutive behavior of salt
Authors: Senseny P. E. 
Published: August 2005

AbstractBorehole closure data have often been used to determine the constitutive behaviour of rock salt. This is an inverse problem and analysis of the data is confused by the fact that borehole closure is a structural response that does not uniquely determine constitutive behaviour since both the stress and deformation depend on the constitutive behaviour.This application brief assesses the conclusion of a recent study that the transient power law, ϵ = K τmtn, which includes no term to account for steady‐state deformation, is a better constitutive model for salt than are models that account for steady‐state straining, and that an empirical model developed from the borehole closure data could be extrapolated to give conservative predictions of long‐term closure of single or widely spaced openings.