bluuebunny/crossref_metadata_2025 huggingface dataset:
A numerical study of the effects of wall deformation on earth pressures
Authors: Potts D. M. , Fourie A. B.
Published: August 2005

When designing any earth retaining structure it is necessary to estimate the limiting earth pressures. This is usually achieved by assuming a linear pressure distrigution and by using active and passive pressure coefficients obtained by either limit equilibrium, stress field solutions of limit analysis. These coefficients are approximate in a theoretical sense, do not distinguish between modes of wall movement, and provide no pre‐failure information. In practice, wall movements are dependent on the construction method and support conditions provided. Any effect of such movements on earth pressures is therefore of practical interest. In this paper the finite element method is used to investigate the effect of the mode of wall movement on the generation of earth pressure. Both smooth and rough walls are considered. It is shown that the distribution of earth pressure is highly dependent on the assumed mode of deformation. The resultant forces on the wall are also affected, but to a lesser degree. The, effect of soil dilatation, the initial horizontal stress and the distribution of soil stiffness with depth are also examined.
Stratified subsoil modelled by a cross‐anisotripic elastic half‐space
Authors: Sekowski Jerzy
Published: August 2005

A method of analysing horizontally stratified subsoil by using as a substiutive model a homogeneous anisotropic elastic half‐space is presented. the material parameters for the substitutive model are dependent on the geometric and mechanical properties of the stratified soil.
Kinematics of axisymmetric vertical slopes at collapse
Authors: Drescher A.
Published: August 2005

This paper discusses the kinematic admissibility of axisymmetric velocity fields for the upper bound stability analysis of slopes surrounding cylindrical openings in frictional materials. The governing kinematic equations for two corner regimes of the Mohr–Coulomb yield condition are analysed. Although the equations can be solved by the method of characteristics, the characteristics and the characteristic relations for each regime differ significantly, for the Haar–von Karman regime the characteristics are non‐orthogonal and strong discontinuities are admissible, whereas for the other regime the characteristics are orthogonal and strong discontinuities must be excluded. Examples of simple velocity fields and the corresponding stability numbers are, given and compared with the partial collapse mechanisms. The solutions are verified against certain inequalities which must be satisfied for kinematical admissibility of axisymmetric velocity fields.
Rheological behaviour effects of non‐Newtonian fracturing fluids on propagation of a vertical hydraulic fracture
Authors: Pascal H.
Published: August 2005

This communication investigates the effects fo the non‐Newtonian behaviour of the fracturing fluids in the hydraulic fracturing mechanism. These effects are illustrated on the propagation of a vertical hydraulic fracture into an oil reservoir, in which the fracturing fluid is of power law and of pseudo‐plastic type. The analytical solutions for evaluating the fracture lengrhs are presented for the cdases of large fluid loss and for no fiuid loss. The results obtained should be useful in the design of fracture treatments, permitting the finding of the rheological properties of the injected fluid for obtaining the desired fracture length and width.
A plasticity model for the mechanical behaviour of anisotropically consolidated clay
Authors: Banerjee P. K. , Yousif N. B.
Published: August 2005

An incremental plasticity theory has been developed to describe the mechanical behaviour of anisotropically consolidated clays. The theory removes some of the shortcomings of the existing critical state models by incorporating the effects of the initial anisotropy due to a known depositional stress history and its subsequent alteration during further plastic deformation under a general stress system.

From the extensive comparisons with the reported results in the literature, it is established that the model is satisfactory in predicting the various aspects of drained as well as undrained behaviour of K0‐consolidated clays.
A probabilistic permeability model and the pore size density function
Authors: Juang C. H. , Holtz R. D.
Published: August 2005

Mathematical interpretation of the pore size disribution (PSD) data as measured by mercury intrusion porosimetry was revealed in detail. The PSD data were commonly presented as cumulative intruded volume per gram of specimen versus pore size. In this paper, however, they were expressed in a dimensionless term for convenient mathematical operations. The pore size density function was deduced from the PSD data using the finite difference approximation and curve‐fitting technique. For the prediction of permeability, first the published correlations between permeability and pore geometry were critically reviewed. A probabilistic permeability model based on the pore size density function was then developed, which can be thought of as a generalization of Childs and Collis‐George's model. Predictions of permeability of the compacted soils studied using the developed model were very good for a wide range of permeabilities.
Constitutive models for rock discontinuities with dilatancy and surface degradation
Authors: Plesha Michael E.
Published: August 2005

A physically motivated constitutive law for the behaviour of geologic discontinuities with dilatancy and contact surface degradation (damage) is presented. In the formulation of the law, the paper distinguishes between macroscopic and microscopic features of the contact surface. Through macroscope considerations. an incremental constitutive law is derived which is applicable to a large class of contact‐friction problems. By idealizing the microstructure to consist of interlocking asperity surfaces, the constitutive equations are specialized for the description of rock joints including effects such as dilatancy, asperity surface degradation and bulking. Several examples are considered demonstrating the law's behaviour and agreement with experimental data. The incremental form of the equations that are derived are amenable to implementation in numerical procedures such as finite element and discrete element (rigid block) computer programs.
Determination of a spatial fracture network
Authors: Thomas A. , Pineau A. , Blin‐Lacroix J. L.
Published: August 2005

Hydraulic and mechanical properties of rock masses are largely dependent upon the distribution and variation of fracture areas. Consequently, it is essential to develop good models for analysing the spatial geometric characteristics of fracture fields. The latter, however, may be ascertained only by measuring open cuts or boreholes. The most important factor from the analysis of areas is to be able to determine spatial networks. Without an exhaustive and expensive inventory, the classical methods involving measurements of dip and strike do not provide either a correct estimation of fracture orientations in space, or a good estimation of their distribution.

At present, automatic analysis of linear traces on large plane areas is used by several authors1,2 and the field strike and dip measurements are applied only for verification purposes. This method of computing spatial networks is especially suitable because of the nature of data so obtained, since it permits various simulations on computed networks. It is based upon classical methods of vector geometry that involve a measurements data matrix and provide a means of solving a double system of equations. Results are the directional spatial fracture densities. The object of this paper is to define the geometric parameters of this problem and the computation method, to present an example and, finally, to conclude with critical comments supported by certain proposals for a variety of applications.
Deformation and fracturing behaviour of discontinuous rock mass and damage mechanics theory
Authors: Kawamoto Toshikazu , Ichikawa Yasuaki , Kyoya Takashi
Published: August 2005

The mechanical behaviour of a rock mass is strongly affected by discontinuities such as faults and joints. In this paper, a damage mechanics theory is proposed which deals with some sets of discontinuities distributed in a rock mass, for example, joint systems. In this theory, the distributed discontinuities are characterized by a second‐order symmetric tensor, called the damage tensor. By introducing the damage concept, the deformation and fracturing behaviour of the rock mass can be reated in a framework of continuum mechanics. A numerical procedure is developed in order to implement the damage mechanics model by using the finite element method. The theory and numerical analysis are applied to several laboratory tests and a practical underground opening problem. Numerical results are compared with measured data.
Lower bound limit analysis using finite elements and linear programming
Authors: Sloan S. W.
Published: August 2005

This paper describes a technique for computing lower bound limit loads in soil mechanics under conditions of plane strain. In order to invoke the lower bound theorem of classical plasticity theory, a perfectly plastic soil model is assumed, which may be either purely cohesive or cohesive‐frictional, together with an associated flow rule. Using a suitable linear approximation of the yield surface, the procedure computes a statically admissible stress field via finite elements and linear programming. The stress field is modelled using linear 3‐noded traingles and statically admissible stress discontinuities may occur at the edges of each triangle. Imposition of the stress‐boundary, equilibrium and yield conditions leads to an expression for the collapse load which is maximized subject to a set of linear constraints on the nodal stresses. Since all of the requirements for a statically admissible solution are satisfied exactly (except for small round‐off errors in the optimization computations), the solution obtained is a strict lower bound on the true collapse load and is therefore ‘safe’.

A major drawback of the technique, as first described by Lysmer,1 is the large amount of computer time required to solve the linear programming problem. This paper shows that this limitation may be avoided by using an active set algorithm, rather than the traditional simplex or revised simplex strategies, to solve the resulting optimization problem. This is due to the nature of the constraint matrix, which is always very sparse and typically has many more rows that columns. It also proved that the procedure can, without modification, be used to derive strict lower bounds for a purely cohesive soil which has increasing strength with depth. This important class of problem is difficult to tackle using conventional methods. A number of examples are given to illustrate the effectiveness of the procedure.
Analysis of one‐dimesional wave propagation in a fluid‐saturated finite soil column
Authors: Hiremath Mahantesh S. , Sandhu Ranbir S. , Morland Leslie W. , Wolfe William E.
Published: August 2005

Biot's dynamic equations of motion for one‐dimensional wave propagation in a fluid‐saturated linear elastic isotropic soil are solved using Laplace transformation followed by numerical inversion and the results compared with a direct finite element formulation. A soil column of finite dimension subjected to velocity boundary conditions is analysed, allowing for reflection of waves from boundaries. Comparison of time histories at given points along the column shows that the finite element solution gives good agreement with the Laplace transform solution for low as well as high drag.
Numerical analysis of the response of reinforced soils to direct shearing: Part 2
Authors: Juran I. , Ider M. H. , Chen C. L. , Guermazi A.
Published: August 2005

A soil‐reinforcement load transfer model was developed by the authors1 to simulate the response of the reinforced soil material to triaxial compression and direct shearing. This paper presents the application of the proposed model for the numerical analysis of direct shear tests on sand samples reinforced with different types of tension resisting reinforcements. A parametric study is conducted to evaluate the effect of the mechanical characteristics and dilatancy properties of the soil, extensibility (elastic modulus) of the reinforcements, and their inclination with respect to the failure surface on the response of the reinforced soil material to direct shearing. An attempt is made to verify the proposed model by comparing numerical test simulations with experimental results reported by Jewell,2 and Gray and Ohashi.3 Comparisons of predicted and experimental results illustrate that the model can provide adequate simulations of the response of the reinforced soil material to shearing. In particular, it allows an evaluation of the effect of soil dilatancy (or contractancy), and extensibility of the reinforcement on tension forces generated in inclusions during shearing.
The influence of out‐of‐plane stress on a plane strain problem in rock mechanics
Authors: Reed M. B.
Published: August 2005

This paper considers the excavation of a cylindrical cavity in a uniformly prestressed mass of brittle Mohr‐Coulomb rock. Previous plane strain displacement solutions have assumed that the out‐of‐plane stress remains the intermediate principal stress at all points. It is here shown that when this assumption breaks down, an inner plastic zone is created in which σr < σz = σθ. A displacement solution is given for this case, using a variable‐dilation plastic flow rule, and results are compared with the previous solution for specific problems. A significant difference is observed only for problems involving a large drop in strength upon yield.
A quadratic variation indirect boundary element method for traction boundary‐value problems of two‐dimensional elastostatics
Authors: Lu Jiali , Watson J. O.
Published: August 2005

Boundary integral equations for traction boundary‐value problems of two‐dimensional elastostatics are derived by the indirect boundary element method. Quadratic variation functions for the representation of geometry, fictitious forces and displacements over each boundary element are described. A system of equations approximating to the boundary integral equations is obtained by a Galerkin formulation in which the integral equation is written at Gauss integration points of elements. The method of computation of the Cauchy principal value is described. Examples of application to the analysis of stress and displacement around underground excavations demonstrate the accuracy and efficiency of the formulation.
A note on finite element simulations of pile driving
Authors: To P. , Smith I. M.
Published: August 2005

The analyses of pile driving using solid, axisymmetric finite elements reported in Reference 1 are extended to different soil conditions and hammer characteristics. Correlation with ‘pile analyser’ procedures is made.
Numerical simulation of secondary consolidation of soil: Finite element application
Authors: Lewis R. W. , Tran D. V.
Published: August 2005

A rheological model has been developed for simulating the secondary consolidation of soils. Numerical procedures have been incorporated into a coupled consolidation program using results from a representative oedometer test. A solution of a two‐dimensional problem has also been performed. The technique is numerically stable and has provided satisfactory predictions for the consolidation settlements and the dissipation of pore water pressure within soils.
An assessment of the bearing capacity of calcareous and silica sands
Authors: Yeung S. K. , Carter J. P.
Published: August 2005

A spherical cavity expansion model has been used to study the bearing capacity of foundations on calcareous and silica sands. Two constitutive models have been used to represent each sand: an elastoplastic, collapse‐softening model, and a computationally simpler, elastic/perfectly plastic material. The predictions of the limit pressures for spherical cavity expansion are compared with laboratory data on the bearing capacities obtained from model footing tests. It is shown that the numerical predictions of the limit pressures correlate well with the experimental values of bearing capacity, particularly at higher effective overburden pressures.
The influence of a boundary fracture on the elastic stiffness of a deeply embedded anchor plate
Authors: Selvadurai A. P. S.
Published: August 2005

The problem of the axial loading of a rigid disk‐shaped anchor plate embedded in an isotropic elastic medium of infinite extent is examined. At the boundary of the disk anchor plate the elastic medium contains a cracked region of finite extent. The presence of the cracked region decreases the elastic stiffness of the anchor plate. The mathematical formulation of the problem is developed, and a numerical scheme is presented which can be used to solve the resulting coupled integral equations. The numerical technique is used to evaluate the results, which illustrate the manner in which the elastic stiffness of the anchor plate is influenced by the extent of cracking. Similar results are developed for the flaw shearing mode stress intensity factor at the external boundary of the cracked region.
Modelling of concrete response to fluctuating load
Authors: Jiang J. , Pietruszczak S.
Published: August 2005

An elastoplastic constitutive model for concrete subjected to cyclic loading conditions is presented. The model is an extension of a recently proposed constitutive concept.7 An initial active loading process is described, using the conventional framework of the rate independent theory of plasticity. An appropriate hardening/softening parameter is introduced which allows one to model the sensitivity of material characteristics to varying confining pressure, including a smooth transition from stable to unstable response. For stress histories that include stress reversals, the formulation invokes a set of neutral loading loci defining the conditions of the neutral state.8 The field of hardening moduli is specified through an appropriate interpolation rule which enables one to simulate adequately the effect of cyclic degradation of the material. The performance of the model is verified for some typical cyclic loading histories, and the results are compared with existing experimental data.
Bifurcation analysis of deep boreholes: II. Scale effect
Authors: Papanastasiou P. C. , Vardoulakis I. G.
Published: August 2005

This paper is a continuation of a previous one on bifurcation of deep boreholes under uniform stress at infinity,1 and it focuses on the effect of borehole radius on borehole stability. Rock is described by the equations of a deformation theory of plasticity for cohesive‐frictional, incompressible materials with Cosserat structure. The inhomogeneous bifurcation problem is formulated and the corresponding eigenvalue problem is solved numerically by the finite element method. It is demonstrated that the combined Cosserat and stress‐gradient effects lead to an increase of the bifurcation stress with decreasing borehole radius (scale effect).
A two‐dimensional poroelastic displacement discontinuity method for hydraulic fracture simulation
Authors: Vandamme L. , Detournay E. , Cheng A. H.‐D.
Published: August 2005

The coupled diffusion and deformation phenomena induced by the opening of a hydraulic fracture in a poroelastic medium are modelled using an extension of the displacement discontinuity method. This method consists in distributing fluid source and poroelastic displacement discontinuity singularities along the locus of the fracture, and over time. As an illustration, the problem of a suddenly pressurized crack in an infinite formation is examined.
An expression for the permeability of anisotropic granular media
Authors: Meegoda Namunu J. , King Ian P. , Arulanandan K.
Published: August 2005

There are many expressions proposed for the permeability of isotropic media based on flow channel and pore size distribution concepts, but there are no such expressions for anisotropic media. In this paper an expression for the permeability of an anisotropic medium is proposed, which has been verified in the laboratory.

The mechanism behind fluid flow through soil was investigated using microscopic computer simulations to propose an expression for macroscopic permeability. The soil was assumed to be a spatially periodic porous medium, and the Navier‐Stokes equation was solved using the FEM with appropriate boundary conditions for several different arrangements of the porous medium. The basic variables influencing flow through soil at the microscopic level were identified as specific surface area, void ratio, particle shape, material heterogeneity and the arrangement of particles in a porous medium. A sensitivity analysis was carried out to obtain an expression for the permeability in terms of the above variables.

The corresponding macroscopic variables for the above microscopic variables are average specific surface area, average void ratio, anisotropy, tortuosity due to material heterogeneity, and the arrangement of particles respectively. An expression for the directional permeability is proposed in terms of these variables for the most common occurrence of particles in a porous medium.

For the verification of the proposed equation, the permeability values of a fine‐grained sand were measured at different void ratios and were compared with those predicted by the proposed equation. The results show that the predicted permeability values from the proposed equation are very close to the measured values.
System analysis in calculation of cantilever retaining walls
Authors: Dembicki Eugeniusz , Chi Tran
Published: August 2005

The paper is concerned with the solution and determination of the optimum shape of a retaining wall modelled by the co‐ordinates of a set of points which belongs to a certain permissible space.

An optimum design method is formulated as a non‐linear multiobjective optimization problem. The following two objective functions, which are mutually conflicting and non‐commensurable with each other, are considered: (a) to minimize the total weight of the wall, (b) to maximize the structure stability.

A set of Pareto optimum solutions is derived numerically by adopting a logical algorithm, and a Pereto optimum solution is obtained by investigating the trade‐off relationships among design objectives.
Thin flow element and the problem of ill‐conditioning
Authors: Valliappan S. , Khalili‐naghadeh N. , Murti V.
Published: August 2005

The problem of ill‐conditioning in anisotropic and heterogeneous flow regions using plane and axisymmetric conditions is studied. A new concept, conditioning ratio, which covers all the possible factors significantly affecting the problem of ill‐conditioning (e.g. aspect ratio, heterogeneity and anisotropy) is proposed. It has been shown that there is an upper limit for this conditioning ratio, beyond which the stiffness matrix of the modelled region will be ill‐conditioned. Using this limiting value and considering the fact that flow behaviour in a single fracture is, basically, independent of the value of permeability normal to the plane of the fracture, k1, a criterion is established to calculate the value of k1 for thin elements. By adopting this criterion the problem of ill‐conditioning could be avoided, regardless of the value of the aspect ratio. The reliability of the proposed criterion is examined by using thin elements with very large aspect ratio (up to 106) in modelling the pumping problem from a well fully intersecting a vertical fracture. The comparison of the numerical results with the available analytical solutions is found to be very satisfactory.
Boundary element approach to the dynamic stiffness functions of circular foundations
Authors: Alarcon E. , Cano J. J. , Dominguez J.
Published: August 2005

A boundary element approach for time harmonic axisymmetric problems using the complete space point load fundamental solution is presented. The fundamental solution is integrated numerically along the azimuthal co‐ordinate of each axisymmetric element. To increase the accuracy of the numerical integration a simple co‐ordinate transformation is proposed. The approach is applied to the computation of the dynamic stiffness functions of rigid circular foundations on layered viscoelastic soils. Three different sites are considered: a uniform half‐space, a soil layer on a half‐space, and a soil consisting of four horizontal layers and a compliant half‐space. The numerical results obtained by the proposed approach for surface circular foundations are very close to corresponding published results obtained by different procedures.
Earth pressure behind a gravity retaining wall
Authors: Bakeer R. M. , Bhatia S. K.
Published: August 2005

This paper presents the results of an investigation of the static earth pressure behind a gravity wall with dry cohesionless backfill. A comparison is made between the results of finite element analyses and those of several experimental studies on wall models. The results of the investigation indicate that current design methods do not account adequately for some parameters that may influence the magnitude and distribution of the earth pressure. The study shows also that the design of earth‐retaining structures should be based on the amount of displacement permitted in the structure.
Analytical model for the design of grouted rock bolts
Authors: Indraratna B. , Kaiser P. K.
Published: August 2005

An analytical model which represents the behaviour of a reinforced rock mass near a circular underground opening in a homogeneous, uniform stress field has been developed. The theory adopts the concepts of elastoplasticity and considers a proper interaction mechanism between the ground and the grouted (or friction) bolts. It highlights the influence of the bolt pattern on the extent of the yield zone and tunnel deformation. A dimensionless parameter is introduced as a design tool which relates the tunnel convergence to the bolt spacing for a given bolt length. This publication contains the derivation of the analytical model and an illustration of the effect of bolts on the stress and displacement field near an opening. Its application to tunnel design is discussed briefly. The verification of the theory by laboratory simulation and field measurements will be presented, in detail, in a future publication.
Instability and ill‐posedness in the deformation of granular materials
Authors: Schaeffer David G.
Published: August 2005

A linear stability analysis of the partial differential equations of granular flow is performed. The constitutive relations include (i) elastic effects, (ii) non‐associated flow rules and (iii) shear‐strain hardening. Conditions for the equations to be well‐posed and to be stable are derived. It turns out that there are two qualitatively different kinds of instability; which appears first depends on the parameters of the constitutive relations. If one kind appears first, then in a constitutive test a period of inhomogeneous deformation is predicted to occur before the formation of shear bands. If the other kind appears first, then shear bands are predicted to form in an approximately homogeneous sample. Some constitutive experiments are analysed from this viewpoint, and the analysis suggests some new experimental work.
Probabilistic foundation stability analysis
Authors: Ronold Knut O.
Published: August 2005

A probabilistic model for stability analysis of a deepwater gravity‐based platform foundation is defined, based on theory for wave loading in conjunction with conventional slip surface considerations. The model accounts for uncertainties in loading as well as in soil properties, and model uncertainties are also considered. The model is updated through in‐service measurements of some of the governing variables, and measurement uncertainties are included. The practical application of the model is illustrated by presentation of calculations for a typical foundation. Probability calculations are performed by first‐order reliability methods.
Double‐porosity modelling of oscillatory gas motion and contaminant transport in a fractured porous medium
Authors: Nilson R. H. , Lie K. H.
Published: August 2005

A double‐porosity model is used to describe the oscillatory gas motion and associated contaminant transport induced by cyclical variations in the barometric pressure at the surface of a fractured porous medium. Flow along the fractures and within the permeable matrix blocks is locally one‐dimensional. The interaction between fractures and blocks includes seepage of fluid as well as diffusion of contaminant. To guard against artificial numerical diffusion, the FRAM filtering remedy and methodology of Chapman is used in calculating the advective fluxes along fractures and within blocks. The entire system of equations, including the fracture‐matrix interaction terms, is solved by a largely implicit non‐iterative algorithm which remains stable and conservative even when the computational time step is large compared to the cross‐block transit time of pressure waves. The numerical accuracy is tested by comparison with exact solutions for oscillatory and unidirectional flows, some of which include diffusion interaction between the fracture and the matrix. The method is used to estimate the rate of vertical transport of radioactive gases through the rubblized chimney produced by an underground nuclear explosion.
Stress strain curve generation from simple triaxial parameters
Authors: Griffiths D. V. , Prevost J. H.
Published: August 2005

A simple hyperbolic function is often used to illustrate typical stress‐strain behaviour of geomaterials during monotonic loading. This approach has the disadvantage that the failure condition is approached asymptotically, whereas in reality failure must occur at a finite value of strain. A modified hyperbolic function with one adjustable parameter is proposed in this paper. The function is shown to be capable of spanning all likely soil stress‐strain data up to and including peak strength.
Finite element analysis of progressive failure in long slopes
Authors: Wiberg N.‐E. , Koponen M. , Runesson K.
Published: August 2005

Progressive failure in long natural clay slopes with an underlying weak shear zone is studied. The clay slope is assumed to be elastic–perfectly plastic, whereas the shear zone may have an elastic–plastic strain softening behaviour. The failure will occur due to the development of large shear deformations in the weak zone. The general behaviour, including the possibility of progressive failure, can be studied by the use of a one‐dimensional finite element model. Other interesting matters which can be studied are critical load, critical disturbance and critical length of the slope. Numerical examples show the overall behaviour due to different residual shear strengths of the weak layer, end disturbance or change of pore pressure in the weak layer. Although simple, the proposed finite element model provides a practically applicable tool for the prediction of whether progressive failure will occur and in which manner the local failure will propagate.
Vertical and horizontal deformation of an inhomogeneous elastic half‐space
Authors: Oner Mete
Published: August 2005

Vertical and horizontal deformations of surface footings have been studied for an inhomogeneous elastic half‐space in which the shear modulus increases with an arbitrary power of depth, n, and Poisson's ratio is constant. A general solution for displacements has been obtained first for point loads applied in vertical and horizontal directions. These are then used in obtaining closed‐form solutions for displacements of uniformly loaded circular and rectangular footings. Finally, a numerical method is described that can be used to analyse a rigid footing of an arbitrary shape, and results for rigid rectangular footings are given.
An endochronic plasticity theory with shear‐volumetric coupling
Authors: Valanis K. C. , Peters J. F.
Published: August 2005

Thermodynamic and physical principles are applied in conjunction with the concepts of endochronic plasticity to develop a theory of constitutive behaviour of soils with dilatant capability. Three separate constitutive models are derived within the framework of the proposed theory, all capable of accounting for shear–volume coupling of soil within the context of endochronic plasticity. One specific model is singled out as the most appropriate on the basis of its analytical simplicity and the plausibility of its thermodynamic and physical foundations. A simple example is worked out for the purposes of illustration.
A BEM–FEM approach for analysis of distresses in pavements
Authors: Subei N. , Saxena S. K. , Mohammadi J.
Published: August 2005

A combined boundary‐element–finite‐element method is presented for the analysis of distresses in pavements subjected to mechanical and environmental effects. Owing to the spatial dimensions of the problem, the non‐homogeneity and the irregular geometry at the pavement joints, a combination of the two methods proves to offer a more realistic solution technique. The advantage of the finite element method (FEM) is in its capabilities of modelling near‐field regions at or around the vicinity of the joint, whereas the boundary element method (BEM) is more suitable to model the far‐field region at infinity.

The three major distresses affecting the serviceability of the pavement system are the temperature, moisture and the applied mechanical loads. The model analyses the stresses and strains resulting from both mechanical and environmental factors in the analysis of a pavement system. Moreover, the infiltration of water through pavement joints, which causes weakening of the subgrade soil, is also analysed. Secondly the curling of the pavement concrete slab under the mechanical and thermal loads and induced friction may cause separation of the pavement structure from its supporting subgrade. Both are treated and modelled in this study. A detailed analysis of the pavement joint with its load transfer device is also performed for the proper assessment of the separation and further extension of the loss of support in the pavement system.
Numerical study of the electrical double‐layer repulsion between non‐parallel clay particles of finite length
Authors: Anandarajah A. , Lu Ning
Published: August 2005

The study presented herein concerns the double‐layer repulsive force that exists between clay particles in a clay–water–electrolyte system. The objective is to examine the nature of the double‐layer repulsive force between two negatively charged clay particles that are inclined to each other and have finite length. The finite element numerical technique is used first to determine the spatial distribution of the electric potential. The net repulsive force and its location are then evaluated from this known distribution of the potential on the basis of the theory of electrostatics. A systematic parametric study is performed by varying certain dimensionless system variables, particularly to investigate the effect of orientation, surface potential and particle length. It is found that for non‐parallel orientation, as the value of inclination and surface potential increase, the repulsive force decreases and its location shifts towards the particle ends that are closer to each other.
Properties of the 20‐node brick
Authors: Smith I. M. , Kidger D. J.
Published: August 2005

Three‐dimensional elastoplastic analyses are increasingly feasible as computing power increases. Candidate finite elements for this work are 20‐node bricks. In elastoplastic situations, yielding creates ‘soft’ regions within a stiffer surrounding matrix and propagation of spurious modes is possible under reduced integration. In this paper, the intrinsic properties of the 20‐node brick are analysed, with a view to avoiding numerical complications in plasticity analyses.
Cavity expansion in sands under drained loading conditions
Authors: Collins I. F. , Pender M. J. , Yan Wang
Published: August 2005

Solutions for the expansion of cylindrical and spherical cavities in sands are presented. The sand is modelled using recently proposed critical‐state models in which the values of the friction and dilation angles depend on the deformation history. Similarity solutions are obtained which enable the limit pressure to be calculated as a function of the initial conditions. Comparisons with existing perfectly plastic theories are made and consequences for the interpretation of cone penetrometer measurements are indicated.
Simulation of excavation in a poro‐elastic material
Authors: Hsi J. P. , Small J. C.
Published: August 2005

A method is presented which allows the computation of the displacements and pore pressures which are generated in an elastic soil when excavation is carried out. The formulation is based on Biot's theory and is fully coupled, with consideration also given to the effects of the lowering of the water table which often accompanies the excavation of soil. Example problems are solved to illustrate the theory which has been presented.
Stress distribution beneath rigid circular foundations on sands
Authors: Balakrishna C. K. , Murthy B. R. Srinivasa , Nagaraj T. S.
Published: August 2005

The calculation of stresses induced inside the soil mass by the foundation loads forms an essential step in most of the geotechnical engineering problems dealing with the probable behaviour of foundations. The distribution of stresses on horizontal planes containing reinforcements at various depths is required in the analysis and design of reinforced soil foundations. An accurate evaluation of contact pressure distribution at the interface is a prerequisite for the computation of stresses inside the soil mass. Of the several approaches the elastic‐plastic approach of computing the contact pressure distribution appears to be reasonable. Using this approach non‐dimensional equations have been derived for calculating the contact pressure distribution beneath rigid circular foundations on sands. The contact pressure distribution so derived has been used for computing the stresses at various points using elastic theory. The results have been graphically presented and are compared with Boussinesq's distribution for uniform contact pressure.
A finite element procedure for calculation of strain from interpolated displacements
Authors: Carr James R.
Published: August 2005

Second‐order universal kriging is proposed as an accurate model for interpolating displacements measured in the field to nodal points of a superimposed finite element mesh. These interpolated displacements are used in a modified finite element procedure to calculate strain. This model is compared to a local trend model to judge superiority. Interpolation models are tested by randomly sampling displacements obtained in a finite element analysis, then applying interpolation in attempts to reconstruct the original results.
Numerical analysis of sampling disturbances in clay soils
Authors: Budhu Muniram , Wu Chang S.
Published: August 2005

In this paper, an insight is provided into the quality of soil samples during the penetration of soil samplers. An updated Lagrangian finite element formulation with the second Piola–Kirchhoff stress rate (the Truesdell stress increment) to account for the large deformation behaviour near the sampling tube is used to determine the mechanical disturbances to a soft clay. The penetration of the sampler is simulated by splitting a group of nodes ahead of the penetration route up to a sufficient depth and applying incremental displacements to match the geometric configuration of the sampling tube. Consolidation effect is included to account for the rate of penetration. Thin‐layer elements are added at the inside wall of the sampling tube to model the soil–sampler interface.

The numerical results show that the central core of the sample is subjected to three distinct stages of vertical strain history, compression–extension–recompression, with the primary irrecoverable disturbances due to the compression stage ahead of the sampler. The degree of disturbance for a frictionless sampler was found to be constant after a penetration depth of 75 per cent of the sample tube diameter, while for a frictional sampler the degree of disturbances keeps increasing as the penetration proceeds. The results of a parametric study to determine the influence on sampling disturbances due to the rate of penetration, the thickness and the tip angle of the sample tube and sampler type are also presented.
The integration of the Melan solution over a line segment—implementation for boundary element modelling of surface excavations
Authors: Meek J. L. , Dai C.
Published: August 2005

In this paper, we have deduced the integration solution of the Melan problem (concentrated force at a point in the infinite half‐plane) over a line segment directly from the two‐dimensional result by the complex variable function method. The BEM dependent on these integration solutions is shown to be valuable for modelling surface and near‐surface excavations. Examples are given of the comparison with Mindlin and analytic solutions.
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

A 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

This 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

In 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

The 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

The 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.