bluuebunny/crossref_metadata_2025 huggingface dataset:
Gravity‐induced stresses near axisymmetric topography of small slope
Authors: McTigue D. F. , Mei C. C.
Published: August 2005

An approximate, analytical solution is found for the gravity‐induced stresses in the neighbourhood of an axisymmetric topographic feature on an elastic half‐space. The solution is in the form of a perturbation expansion in powers of the characteristic slope, ϵ. The leading order problem, at O(1), is for a distributed normal load on a plane half‐space. The O(ϵ) correction is due to a distributed shear traction. The vertical variation of the near‐surface stress perturbation and the rotation of the principal stress directions are O(ϵ) effects, and thus include contribution s of like order from both the normal and shear loads. The method requires general solutions for axisymmetric, normal and shear tractions of arbitrary radial distribution, and these are found in terms of Hankel transforms.
Elasto‐plastic analysis of an underground opening by FEM and coupled FEBEM
Authors: Varadarajan A. , Sharma K. G. , Singh R. B.
Published: August 2005

The elasto‐plastic analysis of a circular underground opening using the finite element method (FEM), the coupled finite element and the boundary element method (FEBEM) is presented. The coupling procedure and elasto‐plastic formulation are discussed. The effect of in situ stress ratio on yielded zone, displaced shape and principal stresses is presented. The results of FEBEM analysis are compared with those obtained from FEM. The computation time and the number of iterations as required by FEBEM and FEM are compared.
Reservoir induced seismicity—a new model
Authors: Saxena S. K. , Ger A. Metin , Sengupta A.
Published: August 2005

Deficiencies of different existing models on ‘Reservoir Induced Seismicity’ have been discussed and a new mathematical model, which enhances a better understanding of triggering mechanism in terms of changes in effective stresses, in situ stresses and water level variations, has been discussed in this paper. In the model fractured rock is simulated by a fluid‐filled elastic material subject to Mohr–Coulomb failure criterion. The model has been found to be capable of responding effectively to site specific attributes. It can recognize and explain the phenomenon of time lag observed in several actual cases. It is also capable of simulating stabilization of rock–reservoir system after a period of activities that follow the initial stage of filling. One dimensional and two dimensional, isotropic and anisotropic cases have been analysed and the model predictions have been found to agree qualitatively with the field observations.
An identification technique for evaluation of phenomenological coefficients in coupled flow in unsaturated soils
Authors: Yong Raymond N. , Xu Da‐Ming
Published: August 2005

To determine moisture movement and heat transfer through an unsaturated soil under temperature and volumetric water content gradients, it is necessary to have knowledge of phenomenological coefficients of the soil. However, in unsaturated flow, i.e. flow through unsaturated soil, these phenomenological coefficients are not constants, but vary with volumetric water content as well as temperature. In this paper, an identification technique is proposed for evaluation of the phenomenological coefficients. The phenomeno‐logical coefficients are first assumed to be certain kinds of functions of volumetric water content and temperature. The choice of the functional forms is based on an understanding of the physical situation, and previous knowledge of water flow in the isothermal case. The constant parameters associated with the functional forms are evaluated through the use of the identification technique. Once these phenomenological coefficients are obtained as certain functions of the volumetric water content and the temperature for a specified soil, analysis of coupled moisture flow and heat transfer in the unsaturated soil can proceed.
Limit analysis slope stability with nonlinear yield condition
Authors: Drescher A. , Christopoulos C.
Published: August 2005

Kinematic 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

In 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

The 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

The 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

Similarity 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

An 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

This 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

An 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

A 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

The 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

A 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

It 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

The 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

This 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

Finite 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

This 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

A 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

Many 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

A 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

A 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

A 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

Finite 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

Borehole 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.
Generalized plasticity and the modelling of soil behaviour
Authors: Pastor M. , Zienkiewicz O. C. , Chan A. H. C.
Published: August 2005

The paper outlines the theory of generalized plasticity in which yield and plastic potential surfaces need not be explicitly defined, and shows how a very effective general model describing the behaviour of sands and of clays under monotonic or transient loading can be developed. The model is currently one of the simplest and yet one of the most effective ones for describing the full range of behaviour.

The hierarchical structure of the model limits the number of parameters which have to be experimentally determined for a given material to those strictly necessary for the problem at hand.

A discussion of currently used models is included.
In‐plane vibrations of soil deposits with variable shear modulus: I. Surface waves
Authors: Vrettos Ch.
Published: August 2005

The propagation characteristics of dispersive SV/P surface waves are analytically studied in a linear‐elastic, isotropic, compressible half‐space with constant mass density and Poisson's ratio and shear modulus increasing according to a continuous, bounded function of depth. Dispersion relations for the particular wave modes are evaluated over wide ranges of the parameters involved. Displacement profiles are presented for typical values of these parameters. Finally, an equivalent depth is given for use in connection with steady‐state vibration techniques for site investigation.
Buckling of layered elastic media: A cosserat‐continuum approach and its validation
Authors: Papamichos E. , Vardoulakis I. , Mühlhaus H.‐B.
Published: August 2005

In this paper the stability of layered, anisotropic, hypoelastic media under initial stress is investigated. The bifurcation problem is formulated and solved numerically by use of a semi‐analytical transfer matrix method. An alternative analytical approach in dealing with inhomogeneous media is developed by representing a periodically layered medium as a homogeneous Cosserat continuum. The Cosserat‐continuum approach is validated against the numerical transfer matrix solution.
A residual force finite element approach to soil–structure interaction analysis
Authors: Lai J. Y. , Booker J. R.
Published: August 2005

An iterative process based upon a hybrid ‘residual force’ method is presented for solving elasto–plastic soil–structure interaction problems. In this approach the soil and the structure are treated as separate bodies and related only by compatibility of displacements and equilibrium of forces at the soil–structure interface. This scheme enables a significant improvement in numerical stability and rate of convergence over the conventional initial stress method. It is also shown that various interface conditions such as shear failure, slip and breakaway, and frictional and dilatant behaviour can be readily accounted for. Some practical aspects associated with the proposed scheme are emphasized for a number of numerical examples.
Interaction of multiple cracks and formation of echelon crack arrays
Authors: Du Yijun , Aydin Atilla
Published: August 2005

Fracturing of rock under compression is a product of a series of processes, including nucleation, growth, interaction and coalescence of multiple microcracks. The formation of echelon arrays of microcracks and macrocracks is one of the crucial rings in the processes. We use a superposition and asymptotic approximation technique to analyse the interaction of multiple cracks with various geometrical configurations. It is shown that crack geometry has a strong influence on crack interaction. Echelon crack arrays produce the strongest interaction and are the preferred geometrical configuration for multiple cracks prior to the formation of through‐going shear fractures. This technique provides parameter‐dependent global behaviour, and is more efficient and easier to use.
Numerical analysis of the shape effect on the tensile strength evaluation of axisymmetric specimens
Authors: Zhang L. C.
Published: August 2005

This paper analyses the shape effect on the tensile strength of axisymmetric rock specimens by an improved adaptive dynamic relaxation method. It is shown that the present approach is convenient and efficient. Numerical results for spheroidal specimens with different shapes reveal the variation of stress distributions along the loading axes and suggest that loading along the shorter principal axis is preferable in strength tests. Furthermore, an empirical formula based on the failure criterion of maximum tensile stress is proposed to evaluate the tensile strength of specimen materials.
Simple shear of isotropic elasto–plastic soil
Authors: Frydman S. , Talesnick M.
Published: August 2005

The implications of assuming isotropic elasto–plasticity to model the behaviour of soil under simple shear conditions are considered. For small strains, use of such a model implies the following three consequences: (1) strains and strain increments at any stage of shearing may be expressed as the sum of elastic and plastic components; (2) principal directions of stress and of plastic strain increment are collinear; (3) principal directions of stress increment and of elastic strain increment are collinear. These consequences are used in order to establish relationships between the stresses, stress increments and strains which develop in a simple shear test. No additional assumptions with regards the form of the yield function, the flow rule or the hardening function are required for this development. By defining the ratio of the plastic to the total shear strain increment on the horizontal plane (the plane of zero extension) as λ, it is possible to define the horizontal normal stress σx in terms of λ and other stresses and strains which are normally known during simple shear loading. As a result, all components of the stress tensor in the simple shear plane may be defined. Results of some direct simple shear tests on soft clay have been interpreted using the model and found to be generally consistent with some of the observations reported in the literature from tests in which boundary stresses were measured.
On the solution of steady unconfined seepage towards semi‐infinite slopes
Authors: Muleshkov Angel , Banerjee Sunirmal
Published: August 2005

Analytical solutions for the two‐dimensional problem of unconfined seepage towards semi‐infinite slopes are described. The analysis employs complex variable techniques. Conformal mappings have been used to reduce the problem to solving an ordinary differential equation. The resulting integrals are presented in terms of special functions. The solutions for the location of the phreatic surface and the exit point have been obtained in parametric form. Some additional results and asymptotic expansions of the solutions are also presented. The numerical results have been calculated and plotted for different values of the slope angle in dimensionless co‐ordinate space.
Response of circular footings and anchor plates in non‐homogeneous elastic soils
Authors: Rajapakse R. K. N. D. , Selvadurai A. P. S.
Published: August 2005

The axisymmetric elastic response of circular footings and anchor plates in a linearly non‐homogeneous elastic soil is analysed. It is assumed that footings/anchors are flexible and subjected to axisymmetric vertical loads. The response of the footing/anchor is modelled by using the classical Poisson–Kirchhoff thin plate theory. A variational technique is used to analyse the interaction problem. A representation for the contact stress is established by using a fundamental solution corresponding to a unit vertical pressure acting over an annular region in the interior of the non‐homogeneous soil. The fundamental solution can be derived by using rigorous analytical procedures. The influence of the footing flexibility and the degree of soil non‐homogeneity on the displacements, bending moments and contact stresses of a surface footing is examined over a wide range of governing parameters. In the case of anchor plates the influence of depth of embedment, degree of soil non‐homogeneity and anchor flexibility on the anchor displacement is investigated.
Axially loaded vertical piles and pile groups in layered soil
Authors: Chin J. T. , Poulos H. G.
Published: August 2005

A numerical method is described for the analysis of axially loaded vertical piles and pile groups embedded in layered soil. The ‘hybrid’ approach is utilized whereby the single‐pile response is represented by load‐transfer (t–z) curves while the pile–soil–pile interaction is obtained accurately using the analytical solutions of Chan et al. for a two‐layered system and in an approximate manner for a Gibson soil. For the single‐pile response a simple rational procedure is suggested for the determination of the averaged rm value (radial distance at which the shear stress becomes negligible). Solutions are presented and compared with the elastic continuum solutions for such soil profiles. Finally, comparisons with actual field measurements of vertical piles and pile groups embedded in such a soil profile show favourable agreement.
A boundary element method for identifying orthotropic material parameters
Authors: Ohkami T. , Ichikawa Y. , Kawamoto T.
Published: August 2005

A new approach is proposed for identifying elastic constants for orthotropic material bodies by using the boundary element method. The material parameters which must be determined are two Young's moduli, a shear modulus and two Poisson's ratios. The method is applied to geotechnical engineering problems.
Comment on the postulate of three plane strain mechanisms
Authors: Gutierrez Marte , Lacasse Suzanne
Published: August 2005

This note discusses the inconsistencies that are inherent in the postulate of three plane strain mechanisms. It is shown that this postulate violates the principle of invariance and one obtains different results depending on the choice of the reference axes. If formulated in the principal stress space, this postulate requires that the principal stress and principal plastic strain increment directions be coaxial. Constitutive models based on this postulate cannot be used for general loading situations involving principal stress rotation where significant non‐coaxiality is obtained.
A non‐linear numerical model for soil mechanics
Authors: Ng T. ‐T. , Dobry R.
Published: August 2005

A new computer program (CONBAL‐2) is developed for 2D numerical simulations of granular soil by random arrays of spheres. CONBAL‐2 uses the discrete‐element method and is based on 3D program TRUBAL, previously presented by Cundall. As in TRUBAL, the new program models a random array of elastic spheres in a periodic space. The main modification of TRUBAL is the implementation by the authors of a rigorous solution for the force–displacement relation at the interparticle contacts. This force‐displacement relation is a function of the elastic constants, friction coefficient and sizes of the spheres, with the properties of quartz used to simulate sand. Other specific features of CONBAL‐2 include its 2D character, the lack of particle rotation and its capability to simulate shear loading on any plane. Simulated laboratory test results are presented using CONBAL‐2 and several random arrays of 531 spheres having two particle sizes. These simulations include monotonic loading drained and undrained (constant volume) ‘triaxial’ experiments, as well as a cyclic‐loading, constant‐volume ‘torsional shear’ test. The stress–strain curves, effective stress paths, volume changes, as well as the ‘pore water pressure’ build‐up behaviour obtained in the simulations compare favourably—qualitatively and in some aspects quantitatively—with similar laboratory results on sands. However, the simulated soil is somewhat stiffer and stronger due to the perfectly rounded particles, limited range of grain sizes, lack of particle rotation and 2D character of the model.
A transient finite element analysis of linear viscoelastic material model
Authors: Wang Yue‐Cong , Murti Viriyawan , Valliappan Somasundaram
Published: August 2005

Since the attenulation of propagating waves through soil/rock is related to the localized material properties as well as the strain developed, the commonly used Rayleigh‐type damping model and its variations are not suitable for dynamic finite element analysis of such materials.

A linear viscoelastic material model based on the concept of the relaxation spectrum is manipualted in place of the damping model in this paper. The method proposed by Day and Minster11 to transform the convolutional form of the stress–strain relationship to a set of differential operators using the Pade approximant method is generalized to non‐scalar waves and implemented for transient finite element analyses. A time‐marching scheme is also proposed to incorporate the resultant differential operators into the governing equation of motion. The accuracy related to the Pade approximant method and the time‐marching scheme is investigated by critically analysing some scalar wave propagation problems. The proposed technique is further verified using two one‐dimensional stress wave propagation problems and a two‐dimensional transient propagating wave through an unbounded linear viscoelastic medium. Some encouraging results have been obtained using the proposed technique and guidelines for using this technique are also presented. Comparisons of analytical solutions obtained by Fourier synthesis and numerical results have been provided.
Modelling and analysis of non‐random uncertainties—fuzzy‐set approach
Authors: Juang C. Hsein , Huang Xin H. , Elton David J.
Published: August 2005

This paper addresses the issue of uncertainty treatment in geotechnical engineering. Emphasis is placed on modelling and analysis of non‐random uncertainties using fuzzy sets. Although uncertainties were modelled with fuzzy sets in this study, subsequent analysis or processing of the uncertain information was performed using traditional, non‐fuzzy techniques. These techniques, including the vertex method and Monte Carlo simulation, are discussed in detail. An example application using soil liquefaction susceptibility is presented. The paper concludes that non‐random uncertainties can be successfully modelled and processed using fuzzy sets.
Finite element modelling of pressuremeter tests and footings on frozen soils
Authors: Puswewala U. G. A. , Rajapakse R. K. N. D. , Domaschuk L. , Lach R. P.
Published: August 2005

A finite element code is developed to model the structure‐frozen soil/ice interaction using a time incrementing, fully implicit, iterative algorithm, and a constitutive model based on the concept that total strain tensor consists of an elastic and a creep component. The code is used to investigate the applicability and limitations of the power law as the creep model for frozen soil by simulating two pressuremeter tests. Two extended phenomenological models based on the generalized power law are used in axisymmetric finite element analyses to simulate two, long‐term, stage‐loaded pressuremeter tests, and comparison of results with test data indicates that one model demonstrates a better ability to approximate the actual response to subsequent load steps, under certain restrictions. Stress analyses demonstrate the ability of the constitutive model to show transient as well as subsequent quasi‐stationary stress stages in creep analysis. Additional simulations of short‐term pressuremeter tests on ice are performed to further illustrate some limitations of the power‐law model. Examples for prediction of creep settlements on frozen geomaterials are demonstrated by considering the interaction of fully flexible circular footings and concrete cylindrical footings (of different embedment depths) with frozen sands.
Prediction of dilation and permeability changes in rock salt
Authors: Stormont J. C. , Daemen J. J. K. , Desai C. S.
Published: August 2005

A numerical procedure has been developed for predicting dilation (porosity) and gas permeability changes in rock salt. The hierarchical single‐surface constitutive model of Desai and co‐workers is used a finite element program to calculate the state of stress and strain surrounding excavations in rock salt. The elastoplastic constitutive model accounts for strain hardening, a non‐associative volumetric response and stress‐path‐dependent behaviour. The calculated stress and strain fields are used in a flow model based on the equivalent channel concept to predict permeability. Parameters for both the mechanical and permeability models are developed from laboratory test results. Two field experiments adjacent to underground excavations are modelled. The extent of the dilated rock zone around the excavation is predicted well, but the magnitude of the porosity and gas permeability is underpredicted very near the excavations. This discrepancy is attributed to model parameters derived from loading‐only laboratory tests, whereas significant unloading occurs in the field. The shape of the yield surface was found to be an important factor in dilation and permeability predictions. Similar stress, strain and permeability fields were obtained with different model types (plane strain or axisymmetric) and initial stress states, and with instantaneous and progressive excavation.
Blast vibration control in the presence of delay scatter and random fluctuations between blastholes
Authors: Blair D. P.
Published: August 2005

It is becoming increasingly important, from an environmental viewpoint, to minimize vibrations induced in urban dwellings by blasting. The present study illustrates how the delay interval between blastholes can be chosen to control and minimize the vibration energy within the structural response band of most houses. In particular, it is shown that the only possibility of reducing such energy is to employ a delay interval in the range 10–35 ms. However, the induced vibrations are also dependent upon the accuracy of the delay initiators as well as the level of random fluctuations between each blasthole signature. It is shown that only very accurate electronic delays give the possibility of utilizing fully the delay sequence in order to control structural vibrations. If the vibration emission from each blasthole is totally uncorrelated with that of any other blasthole then the resulting amplitude spectrum of the blast will be totally unpredictable. This situation occurs irrespective of the delay initiation sequence or its accuracy. Under these conditions it is impossible to predict the blast‐induced energy lying within the structural response band.
Simulation of groundwater flow and contaminant transport at a landfill site using models
Authors: Franz Thomas J. , Rowe R. Kerry
Published: August 2005

Numerical and analytical modelling studies were conducted for the analysis of groundwater flow and contaminant transport at the Innisfil landfill site in the Town of Innisfil, County of Simcoe, in Ontario, Canada. Previously conducted field studies categorized the upper stratigraphy at the site into three units: upper sand unit, upper silt/clay unit and Intermediate Sand unit. Essentially horizontal groundwater movement in the two sand units and vertical downward flow in the silt/clay unit were reported by the field hydrogeologists. In the following, application of three computer models (FLOWPATH, USGS MOC and POLLUTE) for the simulation of the groundwater flow and contaminant transport processes at the Innisfil landfill site is described. The paper focuses on the calibration of groundwater flow and contaminant transport systems, and demonstrates how the insight gained during the contaminant transport calibration was used to improve the initial groundwater flow characterization of the hydrogeological system.