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Micro-scale responses of granular materials under different confining pressures using the discrete element method
Mahmud Sazzad, 2016, izvirni znanstveni članek

Opis: Biaxial compression tests were carried out on assemblies of ovals to study the micro-scale responses of granular materials under different confining pressures using the discrete element method (DEM). A total of 8450 ovals were generated in a rectangular frame without any overlap. Four dense samples were prepared from the initially generated sparse sample under different confining pressures. The simulated results yield a stress-straindilatancy behaviour similar to that observed in sands under different confining pressures. The evolution of the different microparameters and their inter-relationships are established. When the confining pressure is relatively high, the difference between the coordination number and the effective coordination number is very small; however, the difference is apparent for a low confining pressure. The microtopology of the granular assembly at several important states of shear is also reported. It is noted that the topological distribution of the granular materials is confining- pressure dependent. The normalized void-cell number is a minimum under the lowest confining pressure, whereas the same number is a maximum under the highest confining pressure. A linear relationship is observed between the normalized void-cell number and the effective coordination number, regardless of the confining pressures. The evolution of the deviatoric fabric for different confining pressures is measured and the macro-micro relationship is presented.
Ključne besede: microstructures, confining pressure, fabric, microtopology, coordination number, macro-micro relationship
Objavljeno: 15.06.2018; Ogledov: 104; Prenosov: 2
.pdf Celotno besedilo (440,72 KB)

Evaluation of the plastic critical depth in seismic active lateral earth pressure problems using the stress-characteristics method
Amin Keshavarz, 2016, izvirni znanstveni članek

Opis: The plastic critical depth or the conventional tension crack depth has a considerable effect on the active lateral earth pressure in cohesive soils. In this paper the depth for c-ϕ soils has been evaluated in the seismic case using the stress-characteristics or slip-line method. The plastic critical depth was calculated on the basis of the theory of the stress-characteristics method and by considering the horizontal and vertical pseudo-static earthquake coefficients. The proposed solution considers the line of discontinuity in the stress-characteristics network. The earth slope, wall slope, cohesion and friction angle of the soil and the adhesion and the friction angle of the soil-wall interface were considered in the analysis as well. The results show that the plastic critical depths of this study are smaller than those of the other methods and are closer to the modified Mononobe-Okabe method. The effects of the wall and the backfill geometry, the mechanical properties of the soil and the pseudo-static coefficients were studied.
Ključne besede: plastic critical depth, stress characteristics, active lateral earth pressure, seismic
Objavljeno: 15.06.2018; Ogledov: 97; Prenosov: 2
.pdf Celotno besedilo (353,82 KB)

Empirical correlation between the shear-wave velocity and the dynamic probing heavy test
Stjepan Strelec, Davor Stanko, Mario Gazdek, 2016, izvirni znanstveni članek

Opis: Varaždin is located in the north-western part of Croatia in shallow quaternary alluvial sediments of the Drava River basin. Local site effects due to the alluvial soft sediments can play a crucial role in the amplification of seismic-wave ground motions. The shear-wave velocity (VS) is one of the most important parameters for determining dynamic soil properties and ground-response analyses. The seismic surface wave method (MASW) is the simplest and a very efficient way of measuring the shear-wave velocity in the field. The Dynamic Probing Heavy (DPH) test is suited to determining the soil strength and the soil deformation properties. However, there are a lack of correlations between the shear-wave velocity and the DPH tests (VS - NDPH) in the literature. In this paper we present empirical correlations between the shear-wave velocity VS and the soil penetration resistance NDPH with: a) raw (original) NDPH data: VS = 97.839·NDPH0.395, (R2 = 0.723); b) a groundwater correction NDPH data: VS = 92.998·NDPH0.363 (R2 = 0.815). From the measured DPH data, the shear-wave velocity (VS), the shear modulus (Go) and the Young’s modulus (Eo and Er) were estimated. Two different approaches (low vs. high strain) were compared, and the results were found to be in good agreement when the relative difference between the velocities is small and smooth. Dynamic probing tests are good for studying a discrete point of interest in a large field area based on preliminary seismic tests. The suggested correlation VS - NDPH can be used for a rough estimation of VS from NDPH (they are site-specific, and so not applicable worldwide). In this way valuable information about dynamic soil properties can be extracted for ground-response analyses and the study of local site effects.
Ključne besede: shear-wave velocity, MASW, DPH, empirical correlations, dynamic elastic moduli, dynamic soil properties
Objavljeno: 15.06.2018; Ogledov: 93; Prenosov: 1
.pdf Celotno besedilo (1,34 MB)

Corrosion mechanisms for cemented soils in three different sulfate solutions
Pengju Han, Chao Ren, Xiaohong Bai, Frank Chen, 2015, izvirni znanstveni članek

Opis: In order to simulate and study the corrosion effects on the compressive strength of cemented soils that could be exposed in a polluted environment, a series of tests were conducted on cemented soil blocks cured with different concentrations of H2SO4, MgSO4, and Na2SO4 solutions. The test results show that the corrosion degree generally increases with the corrosion time and the solution concentration, while the compressive strength decreases with the increasing corrosion degree. The corrosion degree is highest for the Na2SO4 solution, followed by the MgSO4 and H2SO4 solutions. Namely, when the SO4 2- ion exists in a solution, the corrosion degree for the positive ions follows this descending order: Na+, Mg2+, and H+. X-ray diffraction (XRD) phase analyses were performed for the cemented soil samples after corrosion and ionic concentrations. The results show that the compressive strength decreases with an increase of the Mg2+ concentration in the MgSO4 solution and the Na+ concentration in the Na2SO4 solution. At the same time, the strength increases with an increase of the pH value of the H2SO4 solution. Based on the chemical analysis results, the corrosion of H2SO4 or MgSO4 solutions on cemented soils is deemed as a composite action involving the combined resolving and crystallizing corrosion processes. Furthermore, the corrosion of the Na2SO4 solution of cemented soil is a composite action consisting of dissolving and crystallizing.
Ključne besede: cemented soil, compressive strength, corrosion mechanism, sulfate, pollution, solution
Objavljeno: 15.06.2018; Ogledov: 97; Prenosov: 1
.pdf Celotno besedilo (305,84 KB)

The dry fraction of unsaturated soils
Julio César Leal Vaca, Gustavo Gallegos Fonseca, Eduardo Rojas González, 2015, izvirni znanstveni članek

Opis: An equation to account for the shear strength of unsaturated soils is proposed in this paper. This equation is defined as the equivalent stress, and is an extension of Murray’s equation. This approach applies to the general case of bi-modal structured soils showing a macrostructure and microstructure. The theoretical development considers the existence of a dry fraction in addition to the saturated and unsaturated fractions of the soil. These different fractions are included in a porous model, which allows an evaluation of the parameters of the equivalent stress equation. Finally, the paper includes a comparison between theoretical and experimental results. The comparison shows that the proposed equation can be used to estimate the shear strength of unsaturated soils.
Ključne besede: unsaturated soil, shear strength, equivalent stress, water retention curve
Objavljeno: 15.06.2018; Ogledov: 95; Prenosov: 1
.pdf Celotno besedilo (183,91 KB)

Reinforced piled embankment for a high-speed railway over soft soil
Yan Zhuang, Xiaoyan Cui, 2015, izvirni znanstveni članek

Opis: A geosynthetic, reinforced, piled embankment is an effective and economic method to solve the problems of possible bearing failure, unacceptable settlement and slope instability for an embankment built over soft soil; this has led to its widespread use, especially for high-speed railway embankments. Some design methods have been developed to assess the performance of these reinforced structures, which are mainly based on the results from small-scale models and numerical simulations. However, the reliability of these methods needs to be validated under full-scale field tests. This paper presents a numerical and analytical study for a full-scale field test of the Fengyang high-speed railway embankment. The results were analyzed and discussed in terms of the settlement of subsoil, the stressconcentration ratio (SCR), the axial force and the frictional stress of the pile. They showed that the settlement of the subsoil, from both the finite-element method (FEM) and the analytical method, were in good agreement with the measurement, and thus was a reliable parameter to assess the performance of the piled embankment with reasonable accuracy. The SCR was overestimated by the modified Terzaghi method, with a difference of 25%, while it was underestimated by the FEM, with a difference of approximately 20%. It was also shown that the tensile force in the reinforcement could be effectively assessed using the proposed analytical method, while it was overestimated by the FEM with a difference of 44%.
Ključne besede: reinforced piled embankment, high-speed railway, numerical simulation, analytical method
Objavljeno: 15.06.2018; Ogledov: 67; Prenosov: 1
.pdf Celotno besedilo (578,98 KB)

Numerical modeling of the negative skin friction on single vertical and batter pile
Mohammad Mahdi Hajitaheri Ha, Mahmoud Hassanlourad, 2015, izvirni znanstveni članek

Opis: In this paper the negative skin friction on single vertical and batter piles is investigated. First, a finite-element model (using ABAQUS software) based on the studies Lee et al. and Comodromos and Bareka was developed. After that, the results of the model were compared and validated. Then a single vertical end bearing and a single skin friction pile under different earth-surface loadings were analyzed and the down-drag force as well as the neutral plane location were studied. Subsequently, the performances of the single end bearing and the friction pile, with different inclination angles between 0 and 30º, were analyzed. Moreover, the sensitivity analysis was implemented using 2-D models. This showed a satisfactory compatibility with the results of the study of Lee et al. and Comodromos and Bareka. Finally, it was concluded that the drag load of the pile and the neutral plane position depend on the condition of the soil surrounding the pile, the 2D or 3D model type , the earth-surface loading intensity, the type of end-bearing pile or friction pile and the pile’s inclination angle. The simulation results agree well with the experimental findings.
Ključne besede: negative skin friction, batter pile, down-drag force, neutral plane
Objavljeno: 15.06.2018; Ogledov: 62; Prenosov: 2
.pdf Celotno besedilo (341,89 KB)

A new method for testing the anti-permeability strength of clay failure under a high water pressure
Fu-wei Jiang, Ming-tang Lei, Xiao-zhen Jiang, 2015, izvirni znanstveni članek

Opis: It is difficult to judge the failure of clay seepage under a high water pressure.This paper presents a new method to assess clay failure based on the anti-permeability strength, which is the critical water pressure to destroy the clay. An experiment is designed to test the value that avoids the problem of the time-consuming, traditional method to test clay seepage deformation. The experimental system and the process of testing are introduced in this paper. With a self-designed experimental system and method, 18 groups of sample were tested. The results show that the clay thickness and the seepage paths influence the anti-permeability strength. It also indicates that water infiltrates into the clay under the condition that its pressure exceeds a minimum value (P0).
Ključne besede: clay failure, seepage deformation, anti-permeability strength, high water pressure
Objavljeno: 15.06.2018; Ogledov: 67; Prenosov: 1
.pdf Celotno besedilo (249,24 KB)

A stability assessment of coastal cliffs using digital imagery
Igor Ružić, Čedomir Benac, Ivan Marović, Suzana Ilić, 2015, izvirni znanstveni članek

Opis: The investigated area around the Stara Baška settlement (the island of Krk, NE channel part of the Adriatic Sea) is in a delicate geodynamic balance. Marine erosion is quite prominent and the recorded cliff retreat between 1966 and 2004 was from 4 to 5 metres. The cliff slopes are formed in talus breccias. Strong waves and formations of wave-cut notches are the main causes of the cliff’s instability. The secondary causes are the weathering and erosion of the soil and rocks on the cliff. The slump of the cliff slope can occur in a rock mass with higher strength parameters, where the notches are cut a few metres inward into the toe of the cliff slope. A combined method for the stability analysis of the coastal cliffs was tested; this incorporates the cantilever-beam model and the structure-from-motion (SfM) photogrammetry. This method can provide highly detailed 3D geometrical data of the cliff, which can then be used in the calculations of the stability model. This is particularly important in a stability analysis of lithologically heterogeneous rocks such as breccias with varied geometry, which cannot be easily replaced by a rectangular surface. The simple and useful SfM method overcomes the limitations of traditional surveys in estimating the cliff overhang surface and the notch length.
Ključne besede: marine erosion, cliff stability, SfM photogrammetry, Krk island, Adriatic sea
Objavljeno: 15.06.2018; Ogledov: 59; Prenosov: 2
.pdf Celotno besedilo (865,75 KB)

Numerical simulation of intact rock behaviour via the continuum and Voronoi tesselletion models
Teja Fabjan, Diego Mas Ivars, Vladimir Vukadin, 2015, izvirni znanstveni članek

Opis: The numerical simulation of intact rock microstructure and its influence on macro-scale behaviour has received a lot of attention in the research community in recent years. Generating a grain-like structure with polygonal area contacts is one of the avenues explored for describing the rock’s microstructure. A Voronoi tessellation implemented in the Universal Distinct-Element Code (UDEC) is used to generate models with a polygonal microstructure that represent intact rock. The mechanical behaviour of the Voronoi polygons is defined by micro-properties, which cannot be measured directly in the laboratory. A numerical calibration procedure is needed to produce the macroscopic response of a model that corresponds to the material behaviour measured during a laboratory experiment. In this research, Brazilian, direct tensile, uniaxial compressive and biaxial test models are constructed to simulate the intact rock behaviour under a standard laboratory stress. An extensive series of parametric sensitivity analyses are executed in order to understand the influence of the input micro-properties on every model test behaviour and predict the relation between the micro-properties and the model’s macro response. The results can be treated as general guidelines for a complete and efficient intact rock calibration procedure. In parallel, a continuum-based model using the Mohr-Coulomb constitutive relationship is running as a benchmark. It has been shown that the Voronoi-based models through their microstructure approach better reproduce the Brazilian to direct tensile strength ratio, and show a better representation of the dilation, crack pattern and post-peak behaviour in comparison to continuum models.
Ključne besede: distinct-element method, parametric sensitivity analysis, intact rock, Voronoi tessellation, micromechanical properties, standard laboratory test
Objavljeno: 15.06.2018; Ogledov: 12; Prenosov: 1
.pdf Celotno besedilo (1,57 MB)

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