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2. The dynamic properties of the snail soil from the Ljubljana marshBojan Žlender, Ludvik Trauner, 2007, izvirni znanstveni članek Opis: A series of cyclic triaxial tests was performed on snail-soil samples with different porosities. The cyclic loading was performed with a Wykeham Farrance cyclic triaxial system. The investigation was based on a series of tests in which the following conditions were varied: the initial effective pressures (50, 100, and 150 kPa), the void ratio after consolidation (2.0–1.2) and the cyclic loading expressed by the cyclic stress ratio CSR (0.1–1.0). Measurements were made of the stress, the deformation and the pore-water pressure.
The results of the tests show that interdependency exists between the geomechanical characteristics and the porosity. These relationships can be expressed as functions of the density, the porosity or the water content. It is evident from the results that the changes in the coefficient of permeability, the coefficient of consolidation, and the coefficient of volume compressibility are non-linear with respect to the changes in the porosity. However, the changes at high porosity are much greater than the changes at low porosity, and the changes of the mechanical parameters, such as the Young’s modulus, Poisson’s ratio, and the friction angle, are indistinct and almost linear at lower changes of porosity, and after that become non-linear.
The initial void ratio e is extremely high and the snail soil is liquid after consolidation; a volume strain of εvol > 16 % is needed for the plastic limit state.
The chemical and mineral composition, the particle size distribution and the remains of micro-organisms in the snail soil are constants. In addition, the specific surface is independent of the porosity and the density or unit weight, the porosity and the volume strain are in the well-known correlation.
The performed cyclic triaxial tests show the dynamic characteristics of the snail soil and the influence of the porosity on the cyclic loading strength. The snail soil was recognized as a highly sensitive material. A large strain appears after the initial cycles. The pore pressure, increases already during the first cycle, to the hydrostatic part of the cyclic loading, or more (depending on CSR).
The damping ratio increases exponentially with strain, after some cycles it reach its maximum value, and after that it decreases to the asymptotic value. The reason for such behaviour is the large deformation. The maximum and asymptotic values of the damping ratio are a changed minimum with a void ratio. There is obviously no influence of the porosity on the damping ratio.
The shear modulus is described in relation to shear strain. The increasing of the pore pressure is independent of the porosity until it reaches some value of the pore-pressure ratio (>0.7). Similarly, the increasing of the shear strain becomes dependent on the void ratio until it reaches some particular value of the shear strain (>3%).
The deformation and failure lines for the different porosities are determined from the relationship between the shear stress and the effective stress at some shear strain, after 10 cycles.
The relationships between the shear stress and the effective stress at some value of the pore-pressure ratio are expressed in a similar way.
Two kinds of criteria were used to determine the triggering of liquefaction during the cyclic triaxial tests: first, when the pore pressure becomes equal to the effective confining pressure, and, second, when the axial strain reaches 5% of the double amplitude.
Ključne besede: snail soil, cyclic triaxial test, porosity, permeability, consolidation, Young’s modulus, shear modulus, damping ratio, Poisson’s ratio, friction angle
Objavljeno: 18.05.2018; Ogledov: 141; Prenosov: 1
 Celotno besedilo (479,11 KB) |
3. The degree of deterioration of the tunnels of the Prague Metro based on a monitoring assessmentIvan Vaníček, Martin Vaníček, 2007, izvirni znanstveni članek Opis: Understanding the ageing of structures is a very important issue from the point of view of assessing the risk inherent in those structures. Geotechnical structures, of course, have their own specific risks. This paper is focused on the tunnels of the Prague Metro, looked at from various aspects, i.e., geology, construction systems, and the influence of flooding. The section of the tunnels that was selected for monitoring is one of the most affected, and has a large system of cracked segments. However, even for this affected section the monitoring systems, based on macro- and micro-approaches, showed no significant deterioration was taking place. Nevertheless, for long-term monitoring a wireless system for data collection and transfer was installed and implemented. The results so far have been very positive.
Ključne besede: tunnel, metro, deterioration, ageing, geology, construction, monitoring assessment, MEMS, geophysical, wireless data transfer, metro flooding
Objavljeno: 18.05.2018; Ogledov: 137; Prenosov: 1
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4. A 3D nonlinear dynamic analysis of a rock-fill dam based on IZIIS softwareVioleta Mircevska, Vladimir Bickovski, Mihail Garevski, 2007, izvirni znanstveni članek Opis: This paper treats the 3D nonlinear dynamic behavior of a rock-fill dam based on the Mohr-Coulomb failure criterion. The dam is situated in a steep, narrow, “V-shaped” rigid canyon. The concept of a massless rock foundation is treated, for which a certain part of the rock is included in the model. The dam-rock interface was modeled by contact elements, which allowed certain relative displacements between the two media of different stiffnesses. The generation of the 3D mathematical model was related to the topology of the terrain, and the nonlinear dynamic response was based on the "step-by-step" linear-acceleration direct-integration method, making use of the Wilson-θ method. The convergence process was in accordance with the Newton-Raphson method. First, the initial static effective stresses existing in the conditions of the established stationary filtration through the clayey core were defined. The analysis was based on an original FE program for the static and dynamic analyses of rock-fill dams, as well as a FE program for the solution of the stationary filtration process through the clayey core. The dynamic response of the 3D model of the dam was defined for the effect of harmonic excitations. Dynamic analyses in the linear and nonlinear domains were performed for the purpose of comparing the results. The time histories of the linear and nonlinear responses were defined for selected sections and nodes of the model, the tension cut-off zones, the plastic deformations, and the stress-shear strain relationships. The coefficient against the sliding of the potential sliding surfaces was also defined. It can be concluded that 3D analyses as well as a nonlinear material treatment of the soils built in the dam are imperative for a proper assessment of the stability of rock-fill dams situated in narrow canyons.
Ključne besede: automatic generation of 3D model, rock-fill dam, nonlinear dynamic analysis, elastic perfectly plastic criterion, tension cutoff, cracking zones, plastic deformations, stability
Objavljeno: 18.05.2018; Ogledov: 139; Prenosov: 1
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5. Modeling of the stress-strain behavior in hard soils and soft rocksVladimir Vukadin, 2007, izvirni znanstveni članek Opis: The paper begins with a definition of hard soils and soft rocks (HSSR); this is followed by a short overview of the typical stress-strain behavior of HSSR. It is shown that in spite of the differences in the origin, type and strength of materials, similar stress-strain behaviors can be observed for different materials, ranging from soils to rocks. Based on this observed similarity a theoretical framework can be postulated, with which an appropriate constitutive model for HSSR can be formulated. This model includes the concepts of structure and destructurization as intrinsic material properties. A model named S_BRICK that takes into account the structure and destructurization has been developed and a comparison of this model’s predictions with laboratory results is presented.
Ključne besede: geomechanics, soft rocks, hard soils, stress-strain behaviour, constitutive modeling, structure, destructurization, numerical modeling
Objavljeno: 18.05.2018; Ogledov: 68; Prenosov: 1
Celotno besedilo (679,21 KB) |
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7. The use of the mesh free methods (radial basis functions) in the modeling of radionuclide migration and moving boundery value problemsLeopold Vrankar, Franc Runovc, Goran Turk, 2007, izvirni znanstveni članek Opis: Recently, the mesh free methods (radial basis functions-RBFs) have emerged as a novel computing method in the scientific and engineering computing community. The numerical solution of partial differential equations (PDEs) has been usually obtained by finite difference methods (FDM), finite element methods (FEM) and boundary elements methods (BEM). These conventional numerical methods still have some drawbacks. For example, the construction of the mesh in two or more dimensions is a nontrivial problem. Solving PDEs using radial basis function (RBF) collocations is an attractive alternative to these traditional methods because no tedious mesh generation is required. We compare the mesh free method, which uses radial basis functions, with the traditional finite difference scheme and analytical solutions. We will present some examples of using RBFs in geostatistical analysis of radionuclide migration modeling. The advection-dispersion equation will be used in the Eulerian and Lagrangian forms. Stefan's or moving boundary value problems will also be presented. The position of the moving boundary will be simulated by the moving data centers method and level set method.
Ključne besede: mesh free methods, radial basis functions, finite difference methods, finite elemnt methods, boundary elements methods, geostatistics, Eulerian method, Lagrangian method, level set method
Objavljeno: 18.05.2018; Ogledov: 58; Prenosov: 0
Celotno besedilo (214,16 KB) |
8. Behaviour of the subway tunnel in AlgiersAbdelbaki Seriani, Kismoune Thésard, Tayeb Serradj, 2007, izvirni znanstveni članek Opis: Tunnel construction projects are too expensive to be approached directly without a preliminary small-scale model study and subsequent verification with a mathematical model, if needed. These studies enable to avoid unforeseen consequences which emerge at the time of the project realization. It is within this framework that we carried out our investigations. The behaviour of a subway tunnel in Algiers and the state of transition of the surrounding ground during digging are studied from an experimental point of view via a 1/20 physical model scale.
Ključne besede: tunnel, equivalent material, physical modelling, supports, deformations, rupture, loosened zone
Objavljeno: 18.05.2018; Ogledov: 62; Prenosov: 1
Celotno besedilo (795,52 KB)
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9. Determination of passive earth pressure using three-dimensional failure mechanismHelena Vrecl-Kojc, Stanislav Škrabl, 2007, izvirni znanstveni članek Opis: This paper presents a modified three-dimensional (3D) failure mechanism for determining the 3D passive earth pressure coefficient using the upper bound theorem within the framework of the limit analysis theory. The translational kinematically admissible failure mechanism generalized with a depth of h = 1.0 is considered in the analysis. The mechanism geometry presents a volume of rigid blocks composed of the central body and two lateral rigid bodies, which are connected by a common velocity field. The front surface of the central body interacts with the retaining wall, while the upper surface can be loaded by surcharge loading. The lateral body segments represent four- and three-sided polygons in the cross section of the central body; therefore, they define the polygonal failure surface of the central part. At the outer side, each segment of the lateral body is bounded by infinitesimally spaced rigid half-cones that describe the envelope of a family of half-cones. The numerical results of 3D passive earth pressure limit values are presented by non-dimensional coefficients of passive earth pressure influenced by the soil weight Kpg and a coefficient of passive earth pressure influenced by the surcharge Kpq. This research was intended to improve the lowest values obtained until now using the limit analysis theory. The results are presentedin a graphical form depending on the geometrical parameters and soil properties. A brief description of two world-recognized failure mechanisms based on the limit analysis approach, and the comparison of three failure mechanism results are also presented.
Ključne besede: soil mechanics, passive earth pressure, upper bound theorem, optimization, three-dimensional failure mechanism
Objavljeno: 18.05.2018; Ogledov: 36; Prenosov: 0
Celotno besedilo (504,97 KB) |
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