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Probabilistic study of the phenomenon of crushed grains using the model of Weibull
Kheffache Toufik, Melbouci Bachir, 2012, izvirni znanstveni članek

Opis: The crushing of grains in a granular medium is a very important phenomenon; it is a source of both physical and mechanical changes to these materials. A statistical study of the mechanical properties of a material was used to characterize the distribution and fracture mechanics in order to quantify the evolution of these distributions with sample sizes (grains and whole grains). This work presents the results of an experimental study made on the crushing of individual grains of limestone and samples consisting of multiple grains subjected to a uniaxial loading in order to highlight the influence of the loading and the grain size on the rate of crushing. A statistical study using the Weibull method allowed us to model the problem and quantify the rate of breakage for the two cases. The results obtained show that the rate of deflection depends on the grain size and the intensity of the applied load. Statistical modelling using the Weibull method gave us acceptable results in both cases.
Ključne besede: grain, sample, crushing, statistical study
Objavljeno: 13.06.2018; Ogledov: 57; Prenosov: 3
.pdf Celotno besedilo (335,52 KB)

A new solution for shallow and deep tunnels by considering the gravitational loads
Mohammad Reza Zareifard, Ahmad Fahimifar, 2012, izvirni znanstveni članek

Opis: A new, elasto-plastic, analytical-numerical solution, considering the axial-symmetry condition, for a circular tunnel excavated in a strain-softening and Hoek–Brown rock mass is proposed. To examine the effect of initial stress variations, and also the boundary conditions at the ground surface, the formulations are derived for different directions around the tunnel. Furthermore, the effect of the weight of the plastic zone is taken into account in this regard. As the derived differential equations have no explicit analytical solutions for the plastic zone, the finite-difference method (FDM) is used in this study. On the other hand, analytical expressions are derived for the elastic zone. Several illustrative examples are given to demonstrate the performance of the proposed solution, and to examine the effect of various boundary conditions. It is concluded that the classic solutions, based on the hydrostatic far-field stress, and neglecting the effect of the boundary conditions at the ground surface, give applicable results for a wide range of practical problems. However, ignoring the weight of the plastic zone in the analyses can lead to large errors in the calculations.
Ključne besede: ground-response curve, elasto-plastic analysis, boundary condition, axial symmetry, gravitational loads
Objavljeno: 13.06.2018; Ogledov: 60; Prenosov: 2
.pdf Celotno besedilo (406,96 KB)

Numerical modeling of floating prefabricated vertical drains in layered soil
Ikhya Ikhya, Helmut Schweiger, 2012, izvirni znanstveni članek

Opis: This paper presents a comparison of field measurements and a numerical model of settlements based on the construction of an embankment on soft soil for the Cirebon Power Plant Project in Indonesia, where prefabricated vertical drains (PVDs) were installed. In the numerical model, floating PVDs in two soil layers for two- and one-way drainage conditions are examined in order to determine the optimum penetration depth. In this study, good agreement between the field measurements of the settlements and the numerical prediction could be achieved. An interesting result of this study is that the differences in the stiffness and/or the permeability in the unimproved area below the PVD tip have a significant influence on the optimum penetration depth (L/H) in the two-soil-layer condition. The numerical study showed that it is possible to use floating PVDs in single drainage conditions if the second layer is stiffer and/or more permeable than the first layer.
Ključne besede: two soil layers, floating prefabricated vertical drain, double and single drainage, numerical model, soft clay, consolidation
Objavljeno: 13.06.2018; Ogledov: 52; Prenosov: 3
.pdf Celotno besedilo (727,36 KB)

A comparison between conventional triaxial and plane-strain compression on a particulate system using 3D DEM
Mahmud Sazzad, Kiichi Suzuki, 2012, izvirni znanstveni članek

Opis: Granular materials such as sand are subjected to different stress paths depending on the in-situ conditions. For example, a granular system under the foundations experiences conventional triaxial compression (CTC), while it experiences plane-strain compression (PSC) in the case of the embankment of roads. Due to the difference in the stress paths, the behavior of granular materials also becomes different. This paper aims at comparing the behavior of granular materials under CTC and PSC conditions using the 3D discrete-element method (DEM). An isotropically compressed dense sample consisting of 8000 spheres was prepared numerically using periodic boundaries. The CTC and PSC tests were simulated using the same isotropically compressed dense sample to compare and explore the macro- and micro-mechanical responses of granular materials without any bias from the initial fabric of the numerical sample. Qualitatively, the simulated stress-strain responses are consistent with that observed in the experimental studies. The dilatancy index is found to be independent of the stress paths used in the present study. The b value (defined as b = (σ2 − σ3)/(σ1 − σ3) where σ1, σ2 and σ3 are the stresses in the x1 -, x2 - and x3 - directions, respectively) - axial strain curve has a close similarity with the stress ratio - axial strain curve for the PSC test. The evolution of the coordination number and the sliding contact fraction is independent of the stress paths. A link between the macro- and micro-quantities is observed and a unique macro-micro relationship is noticed, regardless of the stress paths applied in this study.
Ključne besede: conventional triaxial compression, plane-strain compression, micro response, DEM
Objavljeno: 13.06.2018; Ogledov: 55; Prenosov: 2
.pdf Celotno besedilo (257,70 KB)

Soil liquefaction in the Tone river basin during the 2011 earthquake off the Pacific coast of Tohoku
Stanislav Lenart, Junichi Koseki, Yukika Miyashita, 2012, izvirni znanstveni članek

Opis: A brief report about the liquefaction damage in the Tone river basin, caused by the 2011 earthquake off the Pacific coast of Tohoku, is presented. It includes sand boiling, damage to river dikes, the settlement and tilt of superstructures, the uplift of light underground structures and lateral spreading. A history of land reclamation along the Tone river is briefly presented to understand why extensive liquefaction took place predominantly inreclaimed land. The recorded ground motions near the river were analyzed andcompared to near-source ground motions. The effects of the site location and the ground conditions during the peak ground acceleration are discussed.
Ključne besede: 2011 earthquake off the Pacific coast of Tohoku, liquefaction, case history
Objavljeno: 13.06.2018; Ogledov: 59; Prenosov: 2
.pdf Celotno besedilo (1,65 MB)

Ludvik Trauner, 2012, predgovor, spremna beseda

Ključne besede: editorials, scientific journals, geomechanics, geotechnical engineering
Objavljeno: 13.06.2018; Ogledov: 51; Prenosov: 4
.pdf Celotno besedilo (37,85 KB)
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A simplified approach to the settlement estimation of piled rafts
Volkan Kalpakci, Mehmet Yener Özkan, 2012, izvirni znanstveni članek

Opis: In this study, a simplified approach to the settlement estimation of piled rafts resting on over-consolidated clay deposits is presented. For this purpose, a series of plane-strain and three-dimensional analyses were performed and their results are compared with the available data in the literature. It was found that the percentage decrease in the total settlements with the addition of piles with respect to the unpiled case is very closely estimated by both the plane-strain and the three-dimensional, simplified, numerical analyses. Using this phenomenon, a simple method of analysis is suggested for the total settlement estimation of the piled raft foundations and design charts are provided for the cases studied (for the specific soil conditions only) throughout this study.
Ključne besede: piled rafts, settlement, over-consolidated clay, foundation design
Objavljeno: 13.06.2018; Ogledov: 49; Prenosov: 2
.pdf Celotno besedilo (481,96 KB)

Numerical analysis of circular footings on natural clay stabilized with a granular fill
Murat Ornek, Mustafa Laman, Ahmet Demir, Abdulazim Yildiz, 2012, izvirni znanstveni članek

Opis: In this study, numerical predictions of the scale effect for circular footings supported by partially replaced, compacted, layers on natural clay deposits are presented. The scale- effect phenomenon was analyzed according to the footing sizes. Numerical analyses were carried out using an axisymmetric, two-dimensional, finite-element program. Before conducting the analysis, the validity of the constitutive model was validated using field tests performed by authors with seven different footing diameters up to 0.90 m and with three different partial replacement thicknesses. It is shown that the behavior of the circular footings on natural clay soil and the partial replacement system can be reasonably well represented by the Mohr Coulomb model. The Mohr-Coulomb model parameters were derived from the results of conventional laboratory and field tests. After achieving a good consistency between the results of the test and the numerical analysis, the numerical analyses were continued by increasing the footing diameter up to 25 m, considering the partial replacement thickness up to two times the footing diameter. The results of this parametric study showed that the stabilization had a considerable effect on the bearing capacity of the circular footings and for a given value of H/D the magnitude of the ultimate bearing capacity increases in a nonlinear manner with the footing diameter. The Bearing Capacity Ratio (BCR) was defined to evaluate the improved performance of the reinforced system. It was found, based on numerical and field-test results that the BCR of the partially replaced, natural clay deposits increased with an increase in the footing diameter and there was no significant scale effect of the circular footing resting on natural clay deposits.
Ključne besede: scale effect, circular footing, field test, finite-element analysis, natural clay, granular fill
Objavljeno: 13.06.2018; Ogledov: 14; Prenosov: 4
.pdf Celotno besedilo (554,10 KB)

Shallow-landslide spatial structure interpretation using a multi-geophysical approach
Aleksandar Ristić, Biljana Abolmasov, Miro Govedarica, Dušan Petrovački, Aleksandra Ristić, 2012, izvirni znanstveni članek

Opis: We present an methodology for a more detailed and less ambiguous spatial structure interpretation of small, shallow landslides. The spatial structure interpretation of this type of landslides bases on both underground and surface models and requires high-density data. This methodology involves the use of ground-penetrating radar (GPR), electrical resistivity tomography (ERT) and terrestrial laser scanning (TLS) techniques. GPR technique, used for the definition of the underground structure model, provides a time-efficient survey that yields high-resolution data, making it suitable for a shallow subsurface analysis. ERT technique was used only to confirm the results obtained by the GPR survey, since it is more time consuming and more convenient for larger and deeper landslides investigations. The surface model is created using TLS technique, which is time- and cost-effective, produces a large amount of data and is favourable for smaller areas, such as the analysed type of landslides. To the best of the authors’ knowledge, existing procedures based on either conventional or non-invasive geophysical methods, observe, almost exclusively, larger and deeper landslides. Their real-time monitoring involves a number of sensors and is hardly applicable to small landslides because of their number, location and dimensions. Considering the benefits of each applied technique and the interpretation of the results obtained from field data, it is clear that the main advantages of the realized application are the efficiency and applicability for small shallow landslides whose number and impact on the environment are dominant. Therefore, it represents a solid basis for landslide mitigation. The verification of the methodology was made on a small, shallow landslide in the village of Vinča, near Belgrade, Serbia.
Ključne besede: shallow landslide, GPR, ERT, TLS
Objavljeno: 13.06.2018; Ogledov: 13; Prenosov: 2
.pdf Celotno besedilo (1,18 MB)

Yielding in the isotropic compression of Porto silty sand
Miguel Ferreira Amaral, Sara Rios, António Viana da Fonseca, 2012, izvirni znanstveni članek

Opis: The yielding locus of a well-graded silty sand was analysed by means of isotropic compression tests and scanning electron microscopy (SEM). The tests were performed with precise instrumentation, for internal and external strain measurements, and shear-wave velocity measurements by means of bender elements. Finally, aiming at an accurate evaluation of the yield stress, four different methods were applied – two quite well know and the other two being innovative – leading to interesting conclusions.
Ključne besede: silty sand, yield point, isotropic compression, high pressure, seismic waves
Objavljeno: 13.06.2018; Ogledov: 14; Prenosov: 4
.pdf Celotno besedilo (613,18 KB)

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