bluuebunny/crossref_metadata_2025_split huggingface dataset:
A boundary integral method for steady flow in unsaturated porous media
Authors: Martinez M. J. , McTigue D. F. 
Published: August 2005

AbstractThe governing equation for steady flow in a homogeneous, partially saturated, porous medium can be written in a linear form if one adopts a hydraulic conductivity function which varies exponentially with capillary‐pressure head. The resulting linear field equation is a steady Fokker–Planck equation and is well‐suited to numerical solution by the boundary integral equation method (BIEM). The exponential conductivity function is often used in soil physics and is known to be a reasonable approximation over limited ranges of pressure head. A computer code based on the BIEM for obtaining numerical solutions is described and tested. The BIEM is found to exhibit quadratic convergence with element size reduction on smooth solutions and on singular problems, if mesh grading is used. Agreement between results from the BIEM code and a finite element code that solves the fully non‐linear problem is excellent, and is achieved at a substantial advantage in computer processing time. As an illustrative example, the code is applied to determine the distribution of moisture in the vicinity of a tunnel.
A note on non‐linear elasticity of isotropic overconsolidated clays
Authors: Hueckel T. , Tutumluer E. , Pellegrini R. 
Published: August 2005

AbstractAn empirically established rule of Wroth1 for the dependence of the shear modulus on the mean effective pressure and the overconsolidation ratio in clays is investigated within the framework of non‐linear elasticity. The resulting isotropic‐deviatoric coupling is derived and compared to experiments.
Incident P and SV wave scattering effects under different canyon topographic and geological conditions
Authors: Zhao Chongbin , Valliappan S. 
Published: August 2005

AbstractA numerical model for wave scattering problems due to P and SV wave incidences is outlined in this paper. After verifying the present model, a general parametric study on the displacement patterns along the canyons of different shapes due to P and SV wave incidences is also performed. In order to investigate the effects of geologic conditions on ground motions, a weathered V‐shaped canyon, which has different elastic moduli in the weathered layer, is also considered herein. The numerical results from this investigation demonstrated that (1) the present model is very suitable to simulate the problem of P and SV wave scattering along a natural canyon; (2) the shape of a canyon may have important effects on the displacement patterns along the canyon, so that a rectangular canyon is not appropriate to be a dam site due to its high amplification effects on incident waves; (3) the weathered layer on the surface of a canyon will significantly amplify the free field motion, especially for the case of softer weathered layer. Therefore, the excavation or grouting on a dam or a bridge abutment is not only necessary for static stability under static loads, but also beneficial to earthquake resistance because less amplification can be expected for sound rock abutments.
The numerical simulation of seasonal soil drying in an unsaturated clay soil
Authors: Thomas Hywel Rhys , Rees Stephen William 
Published: August 2005

AbstractThe results of a numerical simulation of the observed field‐drying behaviour of an unsaturated clay are described. In particular, the simulation of soil drying during the summer of 1983 is addressed.Richards' pressure‐based unsaturated flow formulation is adopted. Transient numerical solutions are achieved by making use of the finite element method coupled with a finite difference timestepping scheme.The application of the algorithm to the simulation of the problem in hand is described. The initial moisture content distribution represents saturated conditions as indicated by field‐measured data. Boundary conditions are determined from an interpretation of meteorological data. A simple method of representing plant root extraction of soil moisture is proposed.Comparisons of numerical results with field‐measured data collected by British Gas are presented. Good correlation is obtained. The numerical simulation is shown to be capable of representing the observed field‐drying behaviour. The complexity of modelling soil drying, as opposed to infiltration, is clearly illustrated by the work presented.
Derivation of material variability from settlement measurements
Authors: Zeitoun D. G. , Uzan J. 
Published: August 2005

AbstractIn pavement evaluation using non‐destructive testing (NDT), a large amount of deflection bowls are analysed in terms of the elastic moduli of the layers. The results are used to evaluate the material variability, which could serve in an overlay design procedure based on the concept of reliability. The model currently used for interpreting deflection bowls is based on the random variable theory which neglects the spatial distribution of the elastic modulus of the material. Since the subgrade and pavement materials have a spatial distribution, the analysis of NDT could lead to an underestimate of the material variability. The random field theory, which is more adequate than the random variable theory, is presented and used to correct the NDT analysis.The pavement is modelled as a multilayer random elastic medium with, for each layer, a constant Poisson's ratio and a random shear modulus characterized by three statistical moments: average value, standard deviation and autocorrelation function. The stochastic integral formulation presented in the previous publications is generalized here for a multilayer system. The multilayer system is analysed with the random field theory and the covariance matrix of the deflection bowl is obtained and used to generate deflection bowls corresponding to the properties of the random field. These bowls are then interpreted with the current procedure and elastic modulus variabilities are computed. It is found that the current procedure for interpreting deflection bowls underestimates the variability of the subgrade, by a factor of 0.4–1.0. It is interesting to note that the average moduli of the Boussinesq layer and of the two layers are not affected by the type of theory used. The variability of the upper layer in the two‐layer system is also unaffected for a small variation range.
Transient infinite elements for seepage problems in infinite media
Authors: Zhao Chongbin , Valliappan S. 
Published: August 2005

AbstractIn this paper, a time‐dependent infinite element which can be used to simulate transient seepage problems in infinite media is presented. The hydraulic head distribution function of the element has been derived in detail and the property matrices of the element have been well formulated. Since both space and time variables are used in the course of constructing the hydraulic head distribution function of the element, the present infinite element can be referred to as a transient one. Using the present infinite element to model the far field of a system, the mechanism of transient seepage problems in infinite media can be rigorously simulated because the property matrices of the element are evaluated at any time of interest in the analysis. Since explicit expressions can be written for the property matrices of the infinite element, they may be evaluated quite easily and this can be carried out by writing a simple subroutine in a computer program. In order to examine the accuracy and efficiency of the present infinite element, both a one‐dimensional (ID) transient seepage problem in a semi‐infinite medium and a 2D transient seepage problem in a full plane have been solved using the finite and infinite element technique. It has been demonstrated that the present infinite element is very useful for the numerical simulation of transient seepage problems in infinite media.
The axial loading of a rigid circular anchor plate embedded in an elastic half‐space
Authors: Selvadurai A. P. S. 
Published: August 2005

AbstractThe present paper examines the axisymmetric problem related to the loading of a rigid circular anchor plate which is embedded in bonded contact with an isotropic elastic half‐space. A Hankel transform development of the governing equations is used to reduce the associated mixed boundary value problem to a set of coupled Fredholm integral equations of the second kind. These equatons are solved in a numerical fashion to generate results of engineering interest. In particular, the results indicate the influence of the depth of embedment on the axial stiffness of the rigid anchor plate.
Boundary element analysis of contaminant transport in fractured porous media
Authors: Leo C. J. , Booker J. R. 
Published: August 2005

AbstractA two‐dimensional boundary integral method to analyse the flow of contaminant in fractured media having a two‐ or three‐dimensional orthogonal fracture network is presented. The method assumes that the fractures provide the paths of least resistance for transport of contaminants while the matrix, because of its low permeability, acts as ‘storage blocks’ into which the contaminant diffuses. Laplace transform is used to eliminate the time variable in the governing equation in order to facilitate the formulation of a boundary integral equation in the Laplace transform space. Conventional boundary element techniques are applied to solve for the contaminant concentrations at specified locations in the spatial domain. The concentration in the time domain is then obtained by using an efficient inversion technique developed by Talbot. The method is able to analyse the behaviour of waste repositories which have diminishing concentration due to the mass transport of the contaminant into the surrounding fractured media.
Negative skin friction on single piles in a layered half‐space
Authors: Lim C. H , Chow Y. K. , Karunaratne G. P. 
Published: August 2005

AbstractSettlement of the surrounding soil due to surcharge placement may give rise to negative skin friction developed in piles. In this paper, a simple discrete element approach using subgrade reaction method is proposed to analyse negative skin friction on single piles. The pile is embedded in a two‐layer soil where the upper soil layer undergoes consolidation while the lower soil layer acts as a stiffer bearing stratum. Two different and uncoupled deformation modes, one at the pile shaft and the other at the pile toe have been assumed in the determination of the soil stiffness. The effects of a compressible bearing stratum and embedment length of the pile in the bearing stratum are considered in the analysis. This simple approach is verified by comparison with rigorous methods of modelling the soil as an elastic continuum. Three reported case histories are analysed and the computed results are shown to be in reasonable agreement with the field measurements.
Tensile stresses around boreholes due to transient fluid flow
Authors: Chan Derek Y. C. , Hughes Barry D. , Paterson Lincoln 
Published: August 2005

AbstractWe present solutions for the effective stress induced by gas flow through a porous solid into a borehole resulting from sudden pressure reduction. Tensile effective stress that exceeds the strength of the solid will lead to borehole failure. This has applications to the intentional creation of cavities, relevant to the efficient recovery of coalbed methane, and the avoidance of borehole stability problems in conventional gas production.
A semi‐analytical solution procedure for predicting damage evolution at interfaces
Authors: Chen Zhen 
Published: August 2005

AbstractA semi‐analytical solution procedure is developed to predict damage evolution at the interface between two dissimilar geologic materials. The procedure consists of an analytical field solution within each finite element, and a numerical scheme for simulating structural responses. For static problems, an incrementaliterative solution strategy is constructed through the use of an initial elasticity stiffness matrix, and an evolving‐localization constraint in terms of a suitable measure of damage at the most severely damaged element. For simplicity, one‐dimensional problems are considered to illustrate the features of the proposed procedure, and future research is discussed based on the preliminary results obtained.
An approximate numerical analysis of pile–raft interaction
Authors: Poulos H. G. 
Published: August 2005

AbstractThis paper presents an approximate method of numerical analysis of piled–raft foundations in which the raft is modelled as a thin plate and the piles as interacting springs of appropriate stiffness. Allowance is made for the development of limiting pressures below the raft and of the ultimate axial load capacity of the piles.Comparisons between this analysis and existing solutions verify that, despite the approximations involved, the analysis can provide solutions of adequate accuracy for the settlement and pile load distribution within a piled raft.Comparisons are also made with the results of a series of centrifuge tests and with measurements of the performance of a full‐scale piled raft. In both cases, the analysis predicts very well the settlement and proportion of load carried by the piles.
A continuum theory of granular media partially saturated with a viscous fluid
Authors: Pietruszczak S. 
Published: August 2005

AbstractThis paper is concerned with the behaviour of granular media containing voids penetrated by a mixture of viscous liquid and gas (air). It is assumed that, for such materials, the skeleton may be considered as rate‐independent and the sensitivity to the applied loading rate may be attributed to the viscosity of the liquid filling the void space. Within the context of geomechanics, such assumptions appear to be relevant to all coarse‐grained cohesionless materials, including saturated sands. A mathematical formulation for the description of undrained response is presented. The macroscopic properties are estimated based on volume averaging, which is applied to both stress and strain measures within the heterogeneous constituent medium. Numerical examples are provided illustrating the influence of the viscosity of the liquid on the liquefaction potential of a loose granular assembly.
Elastic stress waves in rockbolts subject to impact loading
Authors: Yi Xiaoping , Kaiser Peter K. 
Published: August 2005

AbstractDue to rock bursting or blasting, violent rock ejections can occur. In underground excavations, rockbolts are often used to retain rock blocks that otherwise would be ejected. Employing the stress wave approach, general formulae are derived to compute the elastic stress waves in rockbolts subject to rock block impact loading. Weight‐drop tests on steel rods, simulating impact loading of rockbolts, were performed, and a reasonable agreement is found between theoretical predictions and experimental results. The elastic stress wave in an impact loaded steel rod consists of a rider wave and a lower‐frequency carrier wave. With the same drop height, the carrier wave becomes more sinusoidal as the mass ratio of steel rod to drop weight is decreased.
Comparison of calculational approaches for structural deformation in jointed rock
Authors: Senseny Paul E. , Simons Donald A. 
Published: August 2005

AbstractResults from five different computer models for structural deformation in jointed rock are compared for a problem involving stress‐wave loading of a lined circular tunnel in a jointed medium. The computer models include two discrete element codes, The Direct Interacting Block Systems (DIBS) and The Universal Distinct Element Code (UDEC), and three finite element codes, The Finite Element Code for Largely Explicit Calculation (FLEX), The Explicit Calculations of Interacting Bodies Under Rapid Loading Code (EXCALIBUR), and PRONTO. The finite element codes used either slidelines or joint elements to simulate the motion on joints.All codes had some difficulties with a sequence of preliminary problems solved to ‘shake down’ the computer codes. However, most of the shortcomings of each code were readily overcome. Results showed that three codes could obtain similar answers for tunnel closure, stress around the tunnel and slip on the joints.
Cracking in clays: Solutions to problems in earth structures
Authors: Harison Jack A. , Hardin Bobby O. 
Published: August 2005

AbstractMethods are presented for analysing earth structures subjected to tensile stresses that may produce cracking. The linear elastic fracture mechanics approach is emphasized. Methods of solution are proposed for cracking of a clay layer above the water table due to desiccation; cracking of layered earth structures subjected to external loads; cracking of clay caps for landfills due to differential settlement; and radial cracking in pressurized boreholes. Causes and mechanisms of cracking are discussed for each problem and models pertinent to each problem are proposed. Solutions have been developed by synthesizing analytical and numerical methods. Published experimental data have been incorporated in modelling matric suction and cracked beams on elastic foundations. Finite element analyses were employed to obtain solutions for cracking due to differential settlement and radial cracking in boreholes. The solutions presented herein can be used to assess the soundness of existing structures or to assess the risk of cracking for the design of new structures.
Numerical modelling of transient contaminant migration problems in infinite porous fractured media using finite/infinite element technique. Part I: Theory
Authors: Zhao Chongbin , Valliappan S. 
Published: August 2005

AbstractThe leakage effect in porous fissured media has been considered in a general sense by introducing a new expression of the leakage term in this paper. The double porosity concept is employed and the related expressions are formulated using the upwind finite element approach. Considering the infinite extension of the problem domain, a mapped transient infinite element has been presented to simulate the far field of the infinite medium. Since the mass transfer function of the present mapped transient infinite element is dependent on both space and time variables, the mechanism of transient contaminant migration problems in infinite porous fractured media can be rigorously simulated because the property matrices of the element are evaluated at any time of interest. By comparing the current numerical results with the analytical ones, the accuracy, correctness and effectiveness of the present method have been established. Three different time discretization schemes were examined and it was found that either the central difference or the backward difference approximation is suitable for the upwind finite element simulation of transient contaminant migration problems.
Contaminant leakage from deeply buried cylindrical repositories
Authors: Booker J. R. , Leo C. J. 
Published: August 2005

AbstractThe presence of any leak in a waste repository is going to cause some concern since it may lead to the contamination of the surrounding soil and groundwater. This is an important problem which occurs and recurs, sometimes despite the precautions taken to minimize the possibility of development of any leak. The effects of contaminant leakage in general are not well understood. Thus it is the aim in this paper to develop some semi‐analytical solutions of leakage problems occurring in deeply buried cylindrical repositories. In the solution approach, a series of integral transforms is used to simplify the governing equations and solutions are found in the transform space before numerical inversions are applied to obtain the contaminant concentrations in real space and time. To illustrate the application of the technique, results of some leakage cases are presented.
Simulation of arch dam – foundation interaction with a new friction interface element
Authors: Swoboda G. , Lei X. Y. 
Published: August 2005

AbstractA new model for three‐dimensional non‐linear contact problems with irreversible friction is presented here for the interaction between the rock foundation and an arch dam structure. Based on the finite element method and load incremental theory, a constraint contact element with displacements and contact stresses as node parameters is developed. In this approach, four contact conditions are considered, i.e. fixed, slip, free and mixed. This model can simulate frictional slippage, decoupling and re‐bonding of two bodies initially mating at a common interface or with any initial gaps. Furthermore boundary conditions for this element are discussed and treatment measures proposed. This method is shown to be effective and to have the advantage of being easily implemented into standard finite element programs. Solutions are obtained for a centrally loaded, simply supported composite beam and for an end‐loaded elastica with initial gaps in regional contact with a rigid surface. The results obtained for these examples are compared to the plane stress solutions by contact friction analysis. As an application example, Quanshui arch dam located in Ruyuan County of Guangdong Province in southern China is simulated with the new element.
Finite element modelling for simulating the surface subsidence above a compacting hydrocarbon reservoir
Authors: Lewis R. W. , Sukirman Y. 
Published: August 2005

AbstractThe surface subsidence above a compacting saturated oil reservoir is the main topic of this paper. From a literature review, it is obvious that extensive efforts have been conducted for investigating this phenomenon in various situations. Herein, a numerical model, based on the finite element method, was used for simulating three‐dimensional three‐phase fluid flow in a deforming saturated oil reservoir. The mathematical formulation describes a fully coupled governing equation system which consists of the equilibrium and continuity equations for three immiscible fluids flowing in a porous media. An elastoplastic soil model, based on a Mohr Coulomb yield surface, was utilized. The finite element method was applied to obtain simultaneous solutions to the governing equations where the displacements and the fluid pressures are the primary unknowns. The final discretized equations are solved by a direct solver using fully implicit procedures. A linear analysis was used to study the stability conditions of the present model. Finally, a series of simulations were conducted to indicate the validity and the utility of the developed model.
Zero thickness interface elements—numerical stability and application
Authors: Day R. A. , Potts D. M. 
Published: August 2005

AbstractMany methods have been proposed to model joints in rocks or the interface between soil and a structure. Many analysts have reported numerical problems when using zero thickness interface elements while others have presented satisfactory results without comment of such difficulties. The numerical behaviour of zero thickness interface elements is further investigated in this paper. Some simple examples illustrate the application of interface elements to practical situations and highlight the numerical difficulties that may be encountered. Both ill‐conditioning of the stiffness matrix and high stress gradients were found to cause numerical instability. Ill‐conditioning can be reduced by careful selection of the size of the 2D elements adjacent to the interface. The problem of steep stress gradients is entirely one of inadequate mesh design. Contrary to other reports, this paper shows that the Newton–Cotes integration scheme has no benefit over Gaussian integration.Analyses of a retaining wall using interface elements confirm the analytical values of active and passive earth pressure coefficients which are commonly used in analysis and design of retaining walls.