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1
Content available Parametric study of deep excavation in clays
Mitew-Czajewska M.
Bulletin of the Polish Academy of Sciences. Technical Sciences
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2018
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Vol. 66, nr 5
747--754
EN
The most challenging issue when analyzing geotechnical structures by means of finite element method is the choice of appropriate constitutive soil model, especially with reference to serviceability limit states. The paper presents parametric study of a deep excavation in clays aiming to qualify the applicability of different soil constitutive models in such specific soil conditions. Three types of constitutive models are considered in the paper: linear elastic – perfectly plastic model (Mohr-Coulomb) as a simple and well recognized reference, hypoplastic model (Hypoplastic Clay) and nonlinear elasto-plastic cap models (Hardening Soil and Hardening Soil Small). Numerical analysis was performed using two finite element codes – Plaxis and GEO5 FEM both in 2D space and the results were compared to in-situ displacements measurements. The discussion on the suitability of chosen constitutive models for advanced modelling of deep excavation in preconsolidated clays is presented.
2
Content available A graphical approach to yield and boundary surfaces of selected hypoplastic constitutive equations
Sikora Z., Cieśla P.
Archives of Civil Engineering
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2011
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Vol. 57, nr 2
139-151
EN
The article describes how to identify the boundary and yield surface for hypoplastic constitutive equations proposed by Wu, Gudehus and Bauer. It is shown how to identify and plot the surfaces for any equation in this class. Calculation errors are analyzed characteristic for applied set of numerical formulas. In the paper there are computer links to the source code prepared in the MATLAB system, based on instructions in the article. A sample consitutive domains are shown, plotted using the attached computer program.
PL
W artykule przedstawiono sposób wyznaczania powierzchni płynięcia oraz powierzchni granicznej dla przykładowych równań konstytutywnych w ramach teorii hypoplastyczności zaproponowanych przez Wu, Gudehus'a oraz Bauer'a. Pokazano jak wyznaczać i wykreślać obie powierzchnie dynamicznie dla dowolnych równań tej klasy. Przeanalizowano błędy obliczeniowe charakterystyczne dla użytych formuł numerycznych. W pracy podano linki do komputerowych kodów źródłowych przygotowanych w komercyjnym systemie MATLAB, stosujących instrukcje przedstawione w niniejszym artykule. Przedstawiono przykładowe dziedziny równań konstytutywnych narysowanych przy pomocy załączonego programu komputerowego.
3
Content available Hypoplastic modelling of pre-failure behaviour of sand against experimental data
Głębowicz K.
Archives of Hydro-Engineering and Environmental Mechanics
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2006
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Vol. 53, nr 1
31-47
EN
The aim of this article is to compare experimentally determined strains of sand with theoretical calculations made on the base of the theory of hypoplasticity. During the study `Skarpa' sand was examined in the triaxial apparatus with local measurement of vertical and lateral strains. Results obtained were used to calibrate 8-parameter von Wolffersdorff model. Subsequently, the behaviour of loose and dense sandy samples subjected to different stress paths was predicted.
4
Content available Investigations of shear localization in granular bodies within an anisotropic micro-polar hypoplasticity
Tejchman J.
Archives of Hydro-Engineering and Environmental Mechanics
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2005
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Vol. 52, nr 4
351-371
EN
The paper focuses on the numerical analysis of the effect of texturial anisotropy on shear localization in cohesionless granular materials. For simulation of the mechanical behaviour of a granular material during a monotonous deformation path, a hypoplastic constitutive model was used. To take into account a characteristic length of micro-structure, the constitutive model was extended by micro-polar terms. To take into account texturial effects, the granular hardness was modified. The calculations were carried out with a sand specimen during plane strain compression under constant lateral pressure. A stochastic and uniform distribution of the initial void ratio in the granular specimen was assumed. In addition, shear localization for two different uniform initial void ratios was investigated.
5
Content available Fe-analysis of patterning of shear zones in granular bodies for earth pressure problems of a retaining wall
Tejchman J.
Archives of Hydro-Engineering and Environmental Mechanics
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2004
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Vol. 51, nr 4
317-348
EN
The evolution of shear zones in granular bodies for earth pressure problems of a retaining wall in conditions of plane strain was analyzed. The passive and active failure of a retaining wall was discussed. The calculations were carried out with a rigid and very rough retaining wall undergoing horizontal translation, rotation around the top and rotation around the bottom. The behaviour of dry sand was numerically modelled with a finite element method using a hypoplastic constitutive relation with polar extensions. Attention was paid to the influence of different wall movements on shear localization. The initial void ratio was assumed to be non-uniformly distributed. The geometry of calculated shear zones was compared with corresponding experimental results of laboratory model tests.
6
Content available remote Dynamic measurement and simulation of bulk solids during silo discharge
Ostendorf M., Schwedes J., Antes H., Böhrnsen J. U.
TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk
|
2003
|
Vol. 7, No 4
611-621
EN
This paper deals with the experimental investigation and numerical simulation of silo discharge processes, including dynamic interactions between silo filling and elastic silo walls. The experiments have taken place in a large model silo with a height of 3m and a rectangular base of 800 to 400mm. Optical measurement techniques have been applied to investigate the flow profile, while load cells on the silo walls have registered the stress' evolution, e.g. a stress peak (switch) move from the outlet to the transition of hopper and shaft. The measured data have been compared with simulation results of the Institute of Applied Mechanics at the Technical University of Braunschweig. It has been possible because the numerical simulation examples have been chosen to be similar to the experimental test silo. The discharge process in the simulation is described by a system of nonlinear differential equations. Via the Finite Element Method (FEM) based on an Eulerian reference frame deformation rate, velocity field, porosity and stress distribution can be calculated without the need for re-meshing the FE grid.
7
Content available remote Evolution of shear localisation in earth pressure problems of a retaining wall
Tejchman J.
TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk
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2002
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Vol. 6, No 3
387-410
EN
The paper deals with numerical investigations of the evolution of shear localisation in granular bodies for earth pressure problems of a retaining wall in conditions of plane strain. The passive and active failure of a retaining wall in sand is discussed. The calculations are carried out with a rigid and very rough retaining wall undergoing horizontal translation, rotation around the top and rotation around the bottom. The behaviour of dry sand is numerically modelled with a finite element method using a hypoplastic constitutive relation within a polar (Cosserat) continuum. The constitutive relation is obtained through extension by polar quantities, viz. rotations, curvatures and couple stresses, using the mean grain diameter as a characteristic length. During FE-calculations, the attention is laid on the influence of different wall movements on shear localisation. In addition, the effects of the initial void ratio, distribution of the initial void ratio and mean grain diameter, pressure level and size of the sand body and retaining wall is investigated in the case of a passive wall translation. The FE-results are compared with corresponding experimental results of laboratory model tests.
8
Content available The Consistency conditions for density limits of hypoplastic constitutive law
Niemunis A., Nübel K., Karcher Ch.
TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk
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2000
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Vol. 4, No 3
409-420
EN
The so-called phase diagram of grain skeletons illustrates the range of possible void ratios between the pressure dependent bounds ei and ed. It can be shown that in the framework of the actual hypoplastic model these bounds can be surpassed by particular deformation paths. This inconsistency is particularly acute in recently proposed FE-calculations with density fluctuations. Here we propose a modification to render the formulation consistent.
9
Content available Numerical studies on patterning of shear zone in granular bodies
Tejchman J.
TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk
|
2000
|
Vol. 4, No 3
485-516
EN
The paper deals with numerical investigations on the patterning of shear zones in granular bodies. The behaviour of dry sand during plane strain compression tests was numerically modelled with a finite element method using a hypoplastic constitutive relation within a polar (Cosserat) continuum. The constitutive relation was obtained through an extension of a non-polar one by polar quantities, viz. rotations, curvatures, couple stresses using the mean grain diameter as a characteristic length. This relation can reproduce the essential features of granular bodies during shear localisation. The material constants can be easily determined from element test results and can be estimated from granulometric properties. The attention is laid on the influence of boundary conditions and the distribution of imperfections in the granular specimen on the formation of patterns of shear zones.
10
Content available Modelling of the pressure and density sensitive behaviour of sand within the framework of hypoplasticity
Bauer E.
TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk
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2000
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Vol. 4, No 3
367-388
EN
In this paper a hypoplastic model proposed by Gudehus and Bauer is presented which is apt to describe the mechanical behaviour of loose and dense sand within a wide range of pressures and densities using a single set of constants. State changes are assumed to depend on the current void ratio, the Cauchy stress tensor and the stretching tensor. The constitutive equation is of the rate type and based on non-linear tensor-valued functions. By including a pressure dependent relative density the hypoplastic model describes the influence of pressure and density on the incremental stiffness, the peak friction angle and on the void ratio in a stationary state. The performance of the hypoplastic models is discussed and the results of numerical simulations are compared with experiments.
11
Content available FE-Modelling of behaviour of granular anchors in rock and soils
Wehr J., Tejchman J.
TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk
|
2000
|
Vol. 4, No 3
517-526
EN
The paper is concerned with granular anchors in rock and soils. Model tests and numerical calculations were performed. The effect of different parameters on the behaviour of anchors was investigated: anchor length, anchor diameter, initial density and mean grain diameter of the granular material, anchor roughness and stiffness of the borehole wall. The experiments were modelled with a finite element method and a polar hypoplastic constitutive relation. The relation can capture the salient properties of granular materials during shearing. A satisfactory agreement between experiments and numerical calculations was obtained. Advantages and limitations of granular anchors in rock and soils were outlined.
12
Content available Expansion of a cylindrical cavity in sand
Osinov V. A., Cudmani R.
TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk
|
2000
|
Vol. 4, No 3
421-438
EN
The paper presents numerical solution to the problem of the symmetri quasi-static large-strain expansion of a cylindrical cavity in sand. The boundary value problem is solved with the use of a constitutive equation of hypoplasticity calibrated for a particular sand. As the radius of the cavity increases, the stresses and the density on the cavity surface asymptotically approach limit values which correspond to a so-called critical state of the sand. The limit values depend on the initial stresses and the initial density. The solutions are compared with experimental results for the same sand available in the literature. A comparison is also made with numerical solutions obtained by other authors.
13
Content available Evaluation of liquefaction potential for loose minefill slopes
Kudella P.
TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk
|
2000
|
Vol. 4, No 3
439-452
EN
Uncompacted embankments of certain fine sands exhibit a spontaneous liquefaction potential, which cannot be evaluated basing on undrained shear strength alone. A novel procedure for stability analysis has been developed, basing on Hill's stability criterion and a hypoplastic constitutive law. With given relative densities, assumed initial stress states and variations of perturbation directions, stability or instability of slope sections can be assessed. Catastrophic landslides observed in the past could thus be explained.
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