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Soil Mechanics (soil + mechanic)
Selected AbstractsExplicit integration of bounding surface model for the analysis of earthquake soil liquefactionINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 15 2010Konstantinos I. Andrianopoulos Abstract This paper presents a new plasticity model developed for the simulation of monotonic and cyclic loading of non-cohesive soils and its implementation to the commercial finite-difference code FLAC, using its User-Defined-Model (UDM) capability. The new model incorporates the framework of Critical State Soil Mechanics, while it relies upon bounding surface plasticity with a vanished elastic region to simulate the non-linear soil response. Stress integration of constitutive relations is performed using a recently proposed explicit scheme with automatic error control and substepping, which so far has been employed in the literature only for constitutive models aiming at monotonic loading. The overall accuracy of this scheme is evaluated at element level by simulating cyclic loading along complex stress paths and by using iso-error maps for paths involving change of the Lode angle. The performance of the new constitutive model and its stress integration scheme in complex boundary value problems involving earthquake-induced liquefaction is evaluated, in terms of accuracy and computational cost, via a number of parametric analyses inspired by the successful simulation of the VELACS centrifuge Model Test No. 2 studying the lateral spreading response of a liquefied sand layer. Copyright © 2009 John Wiley & Sons, Ltd. [source] Einbindetiefen und Schnittgrößen bei gestützten Wänden mit beliebiger FußauflagerungBAUTECHNIK, Issue 9 2009Achim Hettler Univ.-Prof. Geotechnik; Bodenmechanik; Geotechnical Engineering; Soil Mechanics Abstract Dieser Beitrag beinhaltet die Ermittlung von Schnittgrößen und Einbindetiefen bei gestützten Wänden. Zunächst wird ein Modell der Fußauflagerung vorgestellt, das sowohl eine freie Auflagerung, eine Teil einspannung als auch eine volle Einspannung umfasst. Die erforderliche Einbindetiefe lässt sich durch Ansatz von Bemessungsgrößen wesentlich einfacher berechnen als am System mit charakteristischen Größen. Bei einer teilweisen Einspannung im Boden können durch Vorgabe eines Drehwinkels im theoretischen Auflagerpunkt die charakteristischen Bodenreaktionen eindeutig festgelegt werden. Für den Fall, dass nur ständige Einwirkungen auftreten, können charakteristische Größen und Bemessungsgrößen durch einen Faktor ineinander umgerechnet werden. Eine weitere Vereinfachung ergibt sich, wenn man, den Empfehlungen des Arbeitskreises "Baugruben" folgend, die veränderlichen Einwirkungen mit einem Erhöhungsfaktor vergrößert und wie für den Lastfall mit ständigen Einwirkungen behandelt. Embedment depths and sectional forces for propped walls with different foot supports. In the following contribution the calculation of the embedment depth and the sectional forces is treated for the case of propped walls. A model for the earth support at the foot of the wall is presented including a free, a partly fixed and a fixed earth support. The determination of the embedment depth at the system with design loads is essentially easier compared to a calculation with characteristic quantities. Assuming a value for the rotation angle at the theoretical foot point of the wall permits to calculate the magnitude of the characteristic soil reactions. In the case that only permanent actions react on the wall, characteristic and design quantities are related by a simple factor. According to the recommendations of excavations a further simplification is possible, if the transient actions are increased by a factor and are treated as in the case of permanent situations. [source] Reduktion der Frosthebungen bei der künstlichen BodenvereisungBAUTECHNIK, Issue 9 2009Guoqing Zhou Prof. Dr.-Ing. Geotechnik; Bodenmechanik; Geotechnical Engineering; Soil Mechanics Abstract Mit dem Ziel der Reduktion der Frosthebungen bei der künstlichen Bodenvereisung wurden die Einflüsse des Temperaturgradienten, der Temperaturänderung sowie der Temperaturänderungsamplitude und -periode der Vereisungstemperatur auf die Frosthebungen bei der eindimensionalen Frosteindringung in feinkörnige Böden experimentell im Labor untersucht. Bei der Frosteindringung in feinkörnige Böden ist die Frosthebung infolge der Bildung der untersten Eislinse (letzte Eislinse bei Frostung von oben nach unten) im thermodynamisch stationären Zustand maßgebend. Der Temperaturgradient beeinflusst zwar die Frosteindringtiefe, die Größe der Frosthebung dagegen nur in geringem Maße. Durch zyklische Veränderungen der Vereisungstemperatur kann das Wachstum der letzten Eislinse beschränkt und dadurch die Frosthebung vermindert werden. Die zyklische Veränderung der Vereisungstemperatur bereits vor der Bildung der letzten Eislinse führt dagegen zu einer großen Frosthebung. Zur Minimierung der Frosthebung müssen die Temperaturveränderungsamplitude und -periode während der Vereisung auf die Eislinsenbildung abgestimmt werden. Decreasing frost heaves of artificial frozen soils by intermission freezing. For decreasing the frost heaves of artificially frozen soils the influences of temperature gradient, its changes as well as the amplitude and period of changing freezing temperature on the one-dimensional frost heaves of fine-grained soils were investigated by experiments in the laboratory. During the frost penetration into the fine-grained soils the frost heaves due to the formation of the final ice lens under thermodynamic stationary condition is decisive. The gradient of temperature influences strongly the depth of frost penetration but only little the total frost heave. Cyclical changes of the freezing temperature can confine the growth of the final ice lens and thereby the frost heave decreases. However, the cyclical changes of the freezing temperature before the formation of the final ice lens can cause a heavy frost heave. For decreasing frost heaves the amplitude und period of changing the freezing temperature must be controlled properly. [source] Untersuchungen zum vertikalen Tragverhalten von SpundwändenBAUTECHNIK, Issue 8 2009Jürgen Grabe Univ.-Prof. Geotechnik; Bodenmechanik; Geotechnical Engineering; Soil Mechanics Abstract Spundwände werden im Wesentlichen auf Biegung infolge einer Belastung durch Erd- und Wasserdrücke beansprucht. Sie können aber auch zum Abtrag von Vertikallasten dienen. Das Tragverhalten von Spundwänden ist bei genauer Betrachtung äußerst komplex, da diesem eine räumlich und zeitlich gekoppelte Boden-Bauwerk-Interaktion zugrunde liegt. Für die praktische Bemessung muss das Tragverhalten daher stark idealisiert werden. Die Rechtfertigung der dafür notwendigen Modellvorstellungen sowie deren Vereinfachungen und Annnahmen sind, wie häufig in der Geotechnik, hauptsächlich durch Erfahrung begründet. Researching the vertical load bearing behaviour of sheet piles. Sheet pile walls are mainly used to carry loads caused by earth and water pressure via bending. In special cases these walls can be used to transfer vertical loads to the subsoil. The complex load bearing behaviour of sheet pile walls is caused by the sterical and temporal coupled soil structure interaction. For practical design the load bearing behaviour needs to be idealised. The apologies used to explain the model conceptions as well as their simplifications are, as usual in geotechnics, mainly motivated by operating experience. [source] Numerical investigation of the effectiveness of a bored pile wall for the minimisation of settlement resulting from tunnel driving.GEOMECHANICS AND TUNNELLING, Issue 6 2009Numerische Untersuchung der Wirkungsweise einer Bohrpfahlwand zur Minimierung der Setzungen infolge Tunnel Soil mechanics; Innovative procedures; Bodenmechanik; Neue Verfahren Abstract Bored pile walls can be constructed between buildings and tunnel alignments to protect sensitive buildings from settlement resulting from tunnelling. The aim of the research work presented here was to evaluate the effectiveness of such a bored pile wall with FE calculations and identify influential parameters. Two methods of predicting settlement were investigated with the programme ABAQUS: The GAP method, where the deformations of the tunnel contour are prescribed, and the stress reduction method, with which the support pressure at the tunnel contour is reduced. The ground is modelled as linear-elastic, ideal-plastic with a Mohr-Coulomb failure criterion as well as with a hypoplastic constitutive law. The contact surface between wall and ground was modelled with complete bonding as well as with a contact law with friction. The simulation results with the stress reduction method and the hypoplastic material model show the best results qualitatively. The predict settlements agree well with empirical methods and centrifuge tests from the literature. The simulations show that the effectiveness of the wall is significantly influenced by the contact properties in the boundary surface. It achieves the best protection effect when frictionless. Zur Abschirmung sensibler Gebäude vor Setzungen infolge Tunnelvortrieb können Bohrpfahlwände zwischen Gebäude und Tunneltrasse eingesetzt werden. Ziel der hier präsentierten Forschungsarbeit war es, die Wirksamkeit einer solchen Bohrpfahlwand mit FE-Berechnungen nachzuvollziehen und Einflussparameter zu identifizieren. Mit dem Programm ABAQUS wurden zwei Möglichkeiten zur Setzungsprognose untersucht: Die GAPMethode, bei der die Verschiebungen der Tunnelkontur vorgegeben werden, und die Spannungsreduktions-Methode, bei welcher der Stützdruck an der Tunnelkontur reduziert wird. Der Boden wurde als linear-elastisch, ideal-plastisch mit Grenzbedingung nach Mohr-Coulomb sowie mit einem hypoplastischen Stoffgesetz modelliert. Die Kontaktfläche zwischen Wand und Boden wurde sowohl mit vollständigem Verbund als auch mit einem Kontaktgesetz mit Reibung modelliert. Die Simulationsergebnisse mit der Spannungsreduktions-Methode und dem hypoplastischen Materialmodell zeigen die qualitativ besten Ergebnisse. Die Setzungsprognosen stimmen gut mit empirischen Ansätzen und Zentrifugenversuchen aus der Literatur überein. Die Simulationen veranschaulichen, dass die Wirksamkeit der Wand maßgeblich von den Kontakteigenschaften in der Grenzfläche beeinflusst wird. Die größte Abschirmwirkung erzielt sie bei Reibungsfreiheit. [source] Soil mechanics and geotechnical controls of channel and hillslope processes Special IssueHYDROLOGICAL PROCESSES, Issue 1 2001Andrew Simon No abstract is available for this article. [source] Action of Force on Rock Mass by Crack Water PressureGEOMECHANICS AND TUNNELLING, Issue 6 2008Guntram Innerhofer Dipl.-Ing. The formula of effective stress used in soil mechanics is adapted to the properties of rock mass by implementation of the wetting factor and the Saint-Venant factor. The wetting factor defines the area over which a hydrostatic force can actually be developed, the Saint Venant factor defines the component of this force which is balanced by reduction of the effective stress in the crack zone. Here, the consequences of this concept are discussed with respect to uniaxial, plain stress and a continuum mechanical model. The effect of the concept is considered in relation to the state of stress in crack zones, and in the adjacent rock mass, and on the action of forces on the system. The development of crack propagation and of shear failure is discussed. The intention is to contribute towards a basic understanding of the complex effects of water pressure in rock masses, applicable to engineering practice. Kraftwirkung des Kluftwasserdrucks auf Fels Die Formel für Effektivspannungen der Bodenmechanik wird, den Eigenschaften von Fels entsprechend, durch Einführen des Benetzungsgrads und des Saint-Venant-Faktors erweitert. Der Benetzungsgrad definiert die Fläche, auf die eine hydrostatische Kraft wirken kann, der Saint-Venant-Faktor die Komponente dieser Kraft, die in der Kluftfläche durch Reduktion der Effektivspannungen ausgeglichen wird. Die andere Komponente belastet das System. Anhand eines einachsigen, eines ebenen und eines Kontinuum-Mechanischen Modells werden die aus diesem Ansatz abgeleiteten Spannungszustände in der Kluftfläche beziehungsweise im klüftigen Fels diskutiert. Die Entwicklung von Kluftsprengung und Scherbruch und das Verhalten hoch- und tiefliegender Druckstollen werden beschrieben. Beabsichtigt ist, mit einer möglichst geschlossenen, auf das Wesentliche beschränkten Darstellung das Verständnis der komplexen Zusammenhänge zu fördern. [source] SANISAND: Simple anisotropic sand plasticity modelINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 8 2008Mahdi Taiebat Abstract SANISAND is the name used for a family of simple anisotropic sand constitutive models developed over the past few years within the framework of critical state soil mechanics and bounding surface plasticity. The existing SANISAND models use a narrow open cone-type yield surface with apex at the origin obeying rotational hardening, which implies that only changes of the stress ratio can cause plastic deformations, while constant stress-ratio loading induces only elastic response. In order to circumvent this limitation, the present member of the SANISAND family introduces a modified eight-curve equation as the analytical description of a narrow but closed cone-type yield surface that obeys rotational and isotropic hardening. This modification enables the prediction of plastic strains during any type of constant stress-ratio loading, a feature lacking from the previous SANISAND models, without losing their well-established predictive capability for all other loading conditions including the cyclic. In the process the plausible assumption is made that the plastic strain rate decomposes in two parts, one due to the change of stress ratio and a second due to loading under constant stress ratio, with isotropic hardening depending on the volumetric component of the latter part only. The model formulation is presented firstly in the triaxial stress space and subsequently its multiaxial generalization is developed following systematically the steps of the triaxial one. A detailed calibration procedure for the model constants is presented, while successful simulation of both drained and undrained behavior of sands under constant and variable stress-ratio loadings at various densities and confining pressures is obtained by the model. Copyright © 2007 John Wiley & Sons, Ltd. [source] Non-isothermal plasticity model for cyclic behaviour of soilsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2008L. Laloui Abstract On the one hand, it has been observed that liquefaction-induced shear deformation of soils accumulates in a cycle-by-cycle pattern. On the other hand, it is known that heating could induce plastic hardening. This study deals with the constitutive modelling of the effect that heat may have on the cyclic mechanical properties of cohesive soils, a relatively new area of interest in soil mechanics. In this paper, after a presentation of the thermo-mechanical framework, a non-isothermal plasticity cyclic model formulation is presented and discussed. The model calibration is described based on data from laboratory sample tests. It includes numerical simulations of triaxial shear tests at various constant temperatures. Then, the model predictions are compared with experimental results and discussed in the final section. Both drained and undrained loading conditions are considered. The proposed constitutive model shows good ability to capture the characteristic features of behaviour. Copyright © 2007 John Wiley & Sons, Ltd. [source] Shearing flows of a dry granular material,hypoplastic constitutive theory and numerical simulationsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2006Chung Fang Abstract In the present study, the Goodman,Cowin theory is extended to incorporate plastic features to construct an elasto-visco-plastic constitutive model for flowing dry granular materials. A thermodynamic analysis, based on the Müller,Liu entropy principle, is performed to derive the equilibrium expressions of the constitutive variables. Non-equilibrium responses are proposed by use of a quasi-linear theory, in particular a hypoplastic-type relation is introduced to model the internal friction and plastic effects. It is illustrated that the Goodman,Cowin theory can appropriately be extended to include frictional effects into the evolution equation of the volume fraction (i.e. the so-called balance of equilibrated force) and the equilibrium expression of the Cauchy stress tensor. The implemented model is applied to investigate conventional steady isothermal granular flows with incompressible grains, namely simple plane shear, inclined gravity-driven and vertical channel-flows, respectively. Numerical results show that the hypoplastic effect plays a significant role in the behaviour of a flowing granular material. The obtained profiles of the velocity and the volume fraction with hypoplastic features are usually sharper and the shear-thinning effect is more significant than that without such plastic effects. This points at the possible wide applicability of the present model in the fields of granular materials and soil mechanics. In addition, the present paper also provides a framework for a possible extension of the hypoplastic theories which can be further undertaken. Copyright © 2006 John Wiley & Sons, Ltd. [source] Development of hyperplasticity models for soil mechanicsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2006S. Likitlersuang Abstract Hyperplasticity theory was developed by Collins and Houlsby (Proc. Roy. Soc. Lon. A 1997; 453:1975,2001) and Houlsby and Puzrin (Int. J. Plasticity 2000; 16(9):1017,1047). Further research has extended the method to continuous hyperplasticity, in which smooth transitions between elastic and plastic behaviour can be modelled. This paper illustrates a development of a new constitutive model for soils using hyperplasticity theory. The research begins with a simple one-dimensional elasticity model. This is extended in stages to an elasto-plastic model with a continuous internal function. The research aims to develop a soil model, which addresses some of the shortcomings of the modified cam-clay model, specifically the fact that it cannot model small strain stiffness, or the effects of immediate stress history. All expressions used are consistent with critical state soil mechanics terminology. Finally, a numerical implementation of the model using a rate-dependent algorithm is described. Copyright © 2005 John Wiley & Sons, Ltd. [source] A hypoplastic constitutive model for claysINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 4 2005D. Ma Abstract This paper presents a new constitutive model for clays. The model is developed on the basis of generalized hypoplasticity principles, which are combined with traditional critical state soil mechanics. The positions of the isotropic normal compression line and the critical state line correspond to the Modified Cam clay model, the Matsuoka,Nakai failure surface is taken as the limit stress criterion and the non-linear behaviour of soils with different overconsolidation ratios is governed by the generalized hypoplastic formulation. The model requires five constitutive parameters, which correspond to the parameters of the Modified Cam clay model and are simple to calibrate on the basis of standard laboratory experiments. This makes the model particularly suitable for practical applications. The basic model may be simply enhanced by the intergranular strain concept, which allows reproducing the behaviour at very small strains. The model is evaluated on the basis of high quality laboratory experiments on reconstituted London clay. Contrary to a reference hypoplastic relation, the proposed model may be applied to highly overconsolidated clays. Improvement of predictions in the small strain range at different stress levels is also demonstrated. Copyright © 2005 John Wiley & Sons, Ltd. [source] Kinematic modelling of shear band localization using discrete finite elementsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 4 2003X. Wang Abstract Modelling shear band is an important problem in analysing failure of earth structures in soil mechanics. Shear banding is the result of localization of deformation in soil masses. Most finite element schemes are unable to model discrete shear band formation and propagation due to the difficulties in modelling strain and displacement discontinuities. In this paper, a framework to generate shear band elements automatically and continuously is developed. The propagating shear band is modelled using discrete shear band elements by splitting the original finite element mesh. The location or orientation of the shear band is not predetermined in the original finite element mesh. Based on the elasto-perfect plasticity with an associated flow rule, empirical bifurcation and location criteria are proposed which make band propagation as realistic as possible. Using the Mohr,Coulomb material model, various results from numerical simulations of biaxial tests and passive earth pressure problems have shown that the proposed framework is able to display actual patterns of shear banding in geomaterials. In the numerical examples, the occurrence of multiple shear bands in biaxial test and in the passive earth pressure problem is confirmed by field and laboratory observations. The effects of mesh density and mesh alignment on the shear band patterns and limit loads are also investigated. Copyright © 2003 John Wiley & Sons, Ltd. [source] | ||||||||||