bluuebunny/crossref_metadata_2025_split huggingface dataset:
Wave‐induced displacements in seafloor sands
Authors: Siddharthan R. 
Published: August 2005

AbstractThe stability and deformation of the seafloor in response to storm wave loading is an important consideration in the design of pipelines, anchors, and offshore structures such as gravity‐and pile‐supported platforms. Two quite different approaches have been proposed for investigating the effects of storm waves on seafloor sands. These approaches derive from quite different considerations of soil‐water interaction.In one of these approaches (exemplified by Yamamoto and Madsen) the seafloor is visualized to be a porous elastic or Coulomb‐damped porous nonlinear medium. In this approach, the response of the seafloor, i.e. the displacements, stresses and porewater pressures, are computed for a given wave. The response is transient and is, therefore, related to the largest wave in the storm wave group.On the other hand, in the approach proposed by Seed and Rahman, only the development of residual porewater pressures (for estimating liquefaction potential) due to the storm wave group are considered. The effects of transient porewater pressures and stresses on the seafloor sands are ignored. The residual porewater pressures are computed using properties based on initial effective stresses through a porewater generation‐dissipation model.The application of these techniques to problems of offshore structures such as pile‐supported platforms has led to considerable uncertainty and confusion. In this paper, both of these approaches are combined to investigate seafloor response to a storm wave group. For typical storm wave conditions that exist in the North Sea, it appears that the inclusion of damping, inertia and anisotropic permeabilities in the study is not important relative to ocean sands. Parametric studies show that, for a given wave, the thickness and the stiffness properties of the soil deposit dictate the response of the deposit. The displacements in the deposit are, therefore, affected by the generation of residual porewater pressures.
Expansion of cavities in layered elastic system
Authors: Sayed S. M. , Hamed M. A. 
Published: August 2005

AbstractTheoretical formulations to the problem of expansion of spherical and cylindrical cavities in a layered elastic system are presented. The medium surrounding the cavity is assumed to consist of several layers, and each is idealized as a linear elastic solid. The solutions are expressed in matrix forms and can be obtained using a programmable calculator. The developed solutions are of some importance in geomechanics. The spherical cavity solution can be used to compute the settlement of single axially loaded piles. The predicted settlement using the analysis outlined herein agrees reasonably well with one case of field measurements. The cylindrical cavity solution can be used to manifest the effect of disturbed mass at the cavity wall on the stress–strain and deformation characteristics of the intact mass.
The time–deflection behaviour of a rigid under‐reamed anchor in a deep clay layer
Authors: Small J. C. , Booker J. R. 
Published: August 2005

AbstractThe behaviour of an under‐reamed anchor in a consolidating soil is examined by approximating the anchor as an impermeable circular plate embedded in a deep soil layer. Hankel and Laplace transforms are applied to the equations governing the consolidation process, and this greatly simplifies the equations, allowing a solution to be obtained for the transformed variables. Numerical inversion of both the Hankel and Laplace transforms is used to obtain the solution at any time.A particular feature of the solution method is that the unknown contact stress between the anchor and the soil and the unknown flows in the plane of the anchor are approximated as a series of simple functions with unknown coefficients. By determining the coefficients of the terms in the series, the complete solution may be found.Computations have been carried out using the method proposed, and results are presented for the time–settlement behaviour of an impermeable anchor. These results are compared with some published and some recomputed finite element data, and this highlights some of the difficulties encountered in using such numerical techniques.
Implicit integration of elastoplastic relations with reference to soils
Authors: Runesson Kenneth 
Published: August 2005

AbstractThe stress solution in plasticity with an associated or a non‐associated flow rule is considered. Upon fully implicit integration of the relevant constitutive relations the stress is obtained as the projection of the (fictitious) elastic stress onto the yield surface for given values of the hardening softening variables. This projection is defined, for a general non‐associated flow rule, in adjusted complementary elastic energy, which becomes exactly the complementary energy when the flow rule is associated.Isotropic elasticity and mean‐stress dependent isotropic yield criteria (pertinent to soil) are considered and the implications of a certain class of non‐associated flow rules are evaluated. This class relates to dilatant (or contractant) materials and involves non‐associated plastic volume change. The corresponding stress solutions are shown to be strongly influenced by Poisson's ratio and by the dilation angle.
A boundary element solution to land subsidence above 3‐D gas/oil reservoirs
Authors: Gambolati Giuseppe , Sartoretto Flavio , Rinaldo Andrea , Ricceri Giuseppe 
Published: August 2005

AbstractA linear boundary element (BE) model is proposed for the uncoupied simulation of land subsidence due to gas, oil and hot water production over three‐dimensional (3‐D) arbitrarily shaped reservoirs. The pore pressure decline is assumed to be specified in advance, e.g. via a numerical model of flow. Use is made of the fundamental solution derived in 1885 by Boussinesq for a vertical load acting upon the traction‐free surface of a semi‐infinite medium. A straightforward application of Betti's (1872) reciprocal theorem allows for the development of a boundary integral whose numerical execution yields directly the downward settlement over the point of interest.The new procedure is applied to assess land sinking caused by an uniform pore pressure decline occurring within fields of elliptical shape and to explore the influence of the assumption of small reservoir thickness which underlies the ‘tension center’ or ‘strain nucleus’ approach previously developed by Geertsma in 1966. The results emphasize the numerical efficiency of the solution and the promising features of the BE method for the evaluation of ground subsidence in 3‐D problems.The present model is based on the theory of the linear poroelasticity and is implemented for a mechanically homogeneous and isotropic half‐space. It allows for any arbitrary geometry of the reservoir and for a non‐uniform distribution of the pore pressure decline. It may easily be extended to other physical settings for which a vertical surface point load solution is available.
An elastoplastic constitutive model for cyclic behaviour of sands
Authors: Hirai Hiroyoshi 
Published: August 2005

AbstractThe constitutive model of sands is proposed to describe the characteristics of plastic behaviour for cyclic loadings. A non‐associated flow rule is used and both yield function and plastic potential are generalized forms of the Modified Cam clay model. The hardening parameter is represented by the plastic work related to different portions of volumetric and deviatoric changes. The boundary surface is employed to describe the plastic strain within the yield surface. The directional independency of yield condition in triaxial compression and extension tests is extended to that in general stress states. Several drained and undrained cyclic tests are predicted and the comparison is made with experimental results. The proposed model is capable of representing the monotonic and cyclic behaviours of sands with reasonable accuracy. The simulation is performed for both included and excluded membrane penetration effects and it is suggested that the membrane penetration causes the significant influences on the results of undrained cyclic tests.
Modelling the elastic behaviour of granular materials
Authors: Lade Poul V. , Nelson Richard B. 
Published: August 2005

AbstractA review of the literature indicates that the elastic behaviour of granular materials is isotropic and that Poissony's ratio is constant, whereas Young's Modulus, the bulk modulus and the shear modulus vary with the mean normal stress and the deviatoric stress. A nonlinear, isotropic model for the elastic behaviour is developed on the basis of theoretical considerations involving the principle of conservation of energy. Energy is therefore neither generated not dissipated in closed‐loop stress paths or in closed‐loop strain paths. The framework for the model consists of Hooke's law, in which Poission's ratio is constant and Young's modulus is expressed as a power function invlving the first invariat of the stress tensor and the second invariant of the deviatoric stress tensor. The characteristics of the model are described, and the accuracy is evaluated by comparison with experimental results from triaxial tests and three‐dimensional cubical triaxial tests with a variety of stress paths. Parameter determination from unloading–reloading cycles in conventional triaxial compression tests is demonstrated, typical parameter values are given for granular materials and extension of the model to soils with effective cohesion is described.
Back analysis procedures for the interpretation of field measurements in geomechanics
Authors: Gioda Giancarlo , Sakurai Shunsuke 
Published: August 2005

AbstractA survey is presented of some recent developments of the numerical techniques for back analysis in the field of geomechanics, with particular reference to tunnelling problems. In the spirit of Terzaghi's observational design method, these techniques are seen as practical tools for interpreting the available field measurements, in order to reduce the uncertainties that in many instances affect the parameters governing the solution of complex geomechanics problems. Both deterministic and probabilistic viewpoints are considered and some significant applications to practical problems are illustrated.
Flow through porous media: A procedure for locating the free surface
Authors: Lacy Sara J. , Prevost Jean H. 
Published: August 2005

AbstractA finite element procedure is developed to accurately locate the free surface of unconfined seepage flow through porous media. The free surface is taken as the boundary between wet and dry soils, with flow in the saturated region characterized by Darcy's law. The method involves equations and meshing which are fully consistent with a general formulation for geotechnical engineering problems involving simultaneous solution of pore fluid pressures and soil skeleton displacements. Accuracy and versatility of the proposed procedure are demonstrated by solving various unconfined seepage flow problems through earth structures. Free surfaces and flownets are presented for the calculated flow fields.
Stress waves in laterally loaded piles
Authors: Wang M. C. , Liao W. P. 
Published: August 2005

AbstractThe behaviour of single vertical piles subjected to lateral loading at the pile head was analysed. Based on the assumption of beam on elastic foundation, the analysis was made by using the method of direct analysis which is a numerical approach making direct use of governing physical laws without explicitly utilizing the differential equation of vibration. The analysis provides short‐time pile response to pulse loadings. These results indicate, among others, that an interaction between the dilatation and shear waves results in a stress discontinuity of considerable magnitude which may deserve special attention in pile design.
Dynamic stress analysis of a class of geomechanics problems by the boundary element method
Authors: Ahmad Shahid 
Published: August 2005

AbstractThis paper presents the application of an advanced BEM for periodic and transient dynamic stress analyses of a class of geomechanics problems. For transient dynamic analysis, the problem is first solved in the Laplace transform space, which happens to be similar to the periodic dynamic analysis, and then the time domain solution is obtained by numerical inversion of transform domain solutions. The numerical implementation of the BEM used to present the results in this paper is complete and most general available to date. It is capable of treating very large, multi‐layered problems by substructuring and satisfying the equilibrium and compatibilities at the interfaces. With the help of this substructuring, capability problems related to layered media and soil–structure interaction have been analysed. A number of examples are presented and through comparisons with available analytical and numerical results, the applicability and usefulness of the present analysis to real geomechanical problems are established.
Prediction of pile capacity from stress‐wave measurements: Some numerical aspects
Authors: Chow Y. K. , Wong K. Y. , Karunaratne G. P. , Lee S. L. 
Published: August 2005

AbstractThe analysis of measured stress waves for the prediction of static pile capacity is described. The usual method of using the measured velocity record as the input boundary condition in a wave equation analysis with a finite element model, if not properly implemented, can lead to significant numerical errors. An alternative scheme using an accurate prescribed displacement procedure with the measured displacement record (obtained from the integration of the velocity) is proposed, and is shown to be very efficient. These aspects of the numerical modelling procedure are illustrated by a case study.
Slope stability analyses for materials with a non‐linear failure envelope
Authors: Collins I. F. , Gunn C. I. M. , Pender M. J. , Yan Wang 
Published: August 2005

AbstractUpper bound techniques are used to analyse the stability of slopes of material failing according to a non‐linear failure criterion, such as closely jointed rocks. The global, extremal nature of upper bound calculations is discussed, as is the inverse use of such procedures for obtaining safe lower bound estimates for material strength properties in back analyses. Specific results are presented for the material model proposed by Hoek and Brown.
Three‐dimensional fracture propagation under specified well‐bore pressure
Authors: Lam K. Y. , Cleary M. P. 
Published: August 2005

AbstractResults are presented for three‐dimensional planar fracture propagation in the presence of variations in confining stress, reservoir properties and frac‐fluid viscosity when the well‐bore pressure is constant throughout the frac‐job. Solid rock deformation during the frac‐job is described by the dislocation method with singular integral equations, and the fluid flow in the fracture is represented by the finite element method. A convergence study is undertaken on the three‐dimensional numerical model, and good agreement is obtained with results from laboratory tests and from the simpler circular model.
Numerical simulation of shear band formation in soils
Authors: Shuttle D. A. , Smith I. M. 
Published: August 2005

AbstractZones of localized shear strain, called bands, are initiated numerically within idealized cohesive and frictional soil specimens both by inhomogeneities and by imperfect boundaries. Qualitatively the results agree with experimental evidence, and give promise of quantitative analyses using better soil models, when the presence of porewater pressures will be of particular significance.
Comparison of dynamic stiffnesses of rigid square and rectangular foundations by DBEM and IBEM
Authors: Ahmad S. , Israil A. S. M. , Chen K. 
Published: August 2005

AbstractIn this work, the Direct and Indirect Boundary Element Methods as applied to dynamic soil structure interaction problems, are compared. Both the methods are used to find the dynamic stiffnesses of rigid surface and embedded foundations. For surface foundations, the results obtained by the two methods were very close for the frequency range considered, but for embedded foundations at higher frequencies, the Indirect Boundary Element Method produced erroneous values for the real part of vertical compliance. The possible reasons for this discrepancy are also studied in this paper.
Upper bound limit analysis using finite elements and linear programming
Authors: Sloan S. W. 
Published: August 2005

AbstractThis paper describes a technique for computing rigorous upper bounds on limit loads under conditions of plane strain. The method assumes a perfectly plastic soil model, which is either purely cohesive or cohesive‐frictional, and employs finite elements in conjunction with the upper bound theorem of classical plasticity theory.The computational procedure uses three‐noded triangular elements with the unknown velocities as the nodal variables. An additional set of unknowns, the plastic multiplier rates, is associated with each element. Kinematically admissible velocity discontinuities are permitted along specified planes within the grid. The finite element formulation of the upper bound theorem leads to a classical linear programming problem where the objective function, which is to be minimized, corresponds to the dissipated power and is expressed in terms of the velocities and plastic multiplier rates. The unknowns are subject to a set of linear constraints arising from the imposition of the flow rulé and velocity boundary conditions. It is shown that the upper bound optimization problem may be solved efficiently by applying an active set algorithm to the dual linear programming problem.Since the computed velocity field satisfies all the conditions of the upper bound theorem, the corresponding limit load is a strict upper bound on the true limit load. Other advantages include the ability to deal with complicated loading, complex geometry and a variety of boundary conditions. Several examples are given to illustrate the effectiveness of the procedure.
Performance of flexible retaining walls supporting dry cohesionless soils under cyclic loads
Authors: Siddharthan Raj , Maragakis Emmanuel M. 
Published: August 2005

AbstractA finite element model is proposed for studying the seismic response of a flexible retaining wall/soil system. The model accounts for nonlinear hysteretic soil behaviour, and also for the increase in lateral stresses and settlement related to grain slip caused by cyclic loads. The response computed by the proposed method was compared with responses recorded at the Cambridge centrifuge facility, and found to be in reasonable agreement. The model was then used to identify the importance of factors such as flexibility of the wall and relative density of the backfill. The study reveals that the maximum bending moments given by current design procedures are nonconservative for stiffer walls. Deflections of flexible walls are of major concern. Flexible walls supporting a sand of medium density yield the greatest deflection.
Undrained and partially drained behaviour of end bearing piles and bells founded in untreated calcarenite
Authors: Murff J. D. 
Published: August 2005

AbstractThe subject paper1 details finite element analyses of underreamed footings installed at the tips of deeply embedded pipe piles. The analysis model incorporated a double‐hardening constitutive law and was calibrated using extensive field and laboratory test results. The results of the study were used to judge the relative effects of various aspects of the design, such as partial drainage and layering. Ultimately, this analysis was used to assess the adequacy of the footings as a remedial strengthening measure for a major offshore platform.
Deformation analysis of sands in cubical and hollow cylinder devices
Authors: Chang Ching S. , Misra Anil , Weeraratne Saroj P. 
Published: August 2005

AbstractFor discrete materials like sands, the continuum field variables, stress and strain, are defined in terms of micro‐level quantities by considering the deformation mechanism of granular soils from a microscopic point of view. Under the application of load, soil is considered to deform due to the movement relative to each other of clusters of particles. Based on this deformation mechanism, the kinematics of soils are developed and a strain tensor for granular soils, in terms of local displacements and geometric measures, is introduced. A local constitutive law relating local displacements and local tractions is defined. Using the local constitutive law, the relationships between stress and strain for the media are developed. The developed model incorporates the influence of strain hardening and material anisotropy on the deformation behaviour of the media. Comparisons of the model predictions and experimental results from tests conducted in cubical and hollow cylinder devices are presented.
A semi‐analytic model for contaminant migration in a regular two‐ or three‐dimensional fractured network: Conservative contaminants
Authors: Rowe R. K. , Booker J. R. 
Published: August 2005

AbstractA new semi‐analytical solution for the transport of a conservative contaminant species in a fractured medium having a regular two‐ or three‐dimensional fracture network is presented. The application of the technique and some of the practical implications arising from an examination of contaminant migration in fractured systems is discussed. Particular consideration is given to the effects of Darcy velocity, fracture spacing, matrix porosity, dispersivity and the mass of contaminant available for transport. The implications of uncertainty with respect to fracture opening size and ground‐water velocity is also discussed and it is shown that provided one can obtain a reasonable estimate of the hydraulic gradient and hydraulic conductivity for the rock mass, uncertainty regarding the magnitude of the opening size and the groundwater velocity does not have a significant effect on predicted contaminant migration for the class of problems being considered.
Horizontal soil stress changes around displacement piles
Authors: Sayed Sayed M. , Clemente Jose L. M. 
Published: August 2005

AbstractA simplified analysis of the problem of horizontal soil stress changes around circular displacement piles, caused by pile placement, is presented. Pile installation is assumed to cause soil displacements in the horizontal direction only, thus yielding an axisymmetric problem. The soil surrounding the pile is modelled as a weightless non‐linear elastic material. Material non‐linearity is handled in a simplified manner by adopting secant shear moduli defined in terms of a proportionality coefficient and a softening factor. The resulting equilibrium equation is solved analytically and an expression is obtained which is also conveniently presented in graphical form. The derived expression can be used to estimate horizontal soil stress changes and is incorporated into a simple procedure to estimate the ultimate load or the efficiency of pile groups. Comparisons are made between efficiencies calculated according to this procedure and efficiencies measured in full‐scale group load tests in sand.