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Rheological properties of marine sediments from the port of Koper
Jasna Smolar, Matej Maček, Ana Petkovšek, 2016, izvirni znanstveni članek

Opis: Subaqueous, fine-grained, cohesive sediments are continuously fluidized by waves and other disturbances that cause their movement, which can be described with numerical models incorporating rheological parameters. The rheological behaviour depends on the soil (solid) type, the volume concentration, the salinity and the testing methods. In this study, rheological investigations of marine sediments from the Port of Koper were carried out by using two coaxial cylinder rheometers (DV3T HB, Brookfield and ConTec Viscometer 5). The influence of the specimen volume, the size of the gap and the type of measuring spindles were analysed and compared. The measured data were evaluated using the Bingham model. For each data set, the boundary between the sheared (“fluid”) and the un-sheared (“solid”) material was calculated and then the calculated boundary was used instead of the outer radius of the cylinder for the evaluation of the rheological parameters, where necessary. A good comparison of the results was found when using this approach. The results are also in agreement with the literature data. The ConTec Viscometer 5, primarily designed for mortars and concrete, was shown to be also suitable for the investigation of sediments.
Ključne besede: marine sediments, Bingham model, yield stress, plastic viscosity, coaxial cylinder rheometer, plug flow, Bay of Koper
Objavljeno: 18.06.2018; Ogledov: 486; Prenosov: 42
.pdf Celotno besedilo (709,57 KB)
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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: 648; Prenosov: 31
.pdf Celotno besedilo (353,82 KB)
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Post-liquefaction volume change in micaceous sandy of Old Gediz River Delta
Ender Basari, Gurkan Ozden, 2013, izvirni znanstveni članek

Opis: Post-liquefaction settlement characteristics of micaceous sands are not well investigated topic. Currently available charts relating post-liquefaction volumetric strain to relative density were developed for clean sand. Estimation of post-liquefaction settlement of micaceous sands, therefore, may stay on the unsafe side, since there is evidence indicating that mica grains could increase volume change tendency. Influence of mica content on post-liquefaction volumetric strain of sand-mica mixtures is studied in this article. Soil samples were prepared at various relative densities. Influence of fine content that could be present in the field was also investigated on tamped natural field samples recovered from boreholes drilled in a highly populated alluvial site known as the Old Gediz River Delta of Izmir. It was found that increasing mica content at a certain relative density resulted in higher volumetric strains as compared with the data on clean sands. It is deduced that influence of mica grains on sand behavior depends on initial void ratio of sand. Effects of mica grains decrease with increasing of relative density. Simple empirical relationships were derived relating mica content and relative density to volumetric strain. It was also noticed that fine content accelerated and increased post-liquefaction volumetric strains.
Ključne besede: sand, mica, non-plastic fines, post-liquefaction volume change
Objavljeno: 14.06.2018; Ogledov: 322; Prenosov: 63
.pdf Celotno besedilo (434,60 KB)
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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: 561; Prenosov: 58
.pdf Celotno besedilo (406,96 KB)
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Prediction of the pile behaviour under dynamic loading using embedded strain sensor technology
Andrej Štrukelj, Mirko Pšunder, Helena Vrecl-Kojc, Ludvik Trauner, 2009, izvirni znanstveni članek

Opis: A standard dynamic loading test of the pile was performed on the highway section Slivnica - Hajdina near Maribor, Slovenia. Parallel to standard testing procedures the new monitoring technology based on specially developed strain sensors installed inside the pile body along the pile axis was introduced. On the basis of the measured results the normal strains along the pile axis were measured. Taking into consideration the elastic modulus of the concrete the normal stresses in the axial direction of the pile were also calculated and afterwards the shear stresses along the pile shaft have been estimated as well as the normal stresses below the pile toe. The estimation was made by considering a constant value for the pile diameter. The measured results were also compared with the computer simulation of the pile and the soil behaviour during all the successive test phases. The strain measurements inside the pile body during the standard dynamic loading test in present case did not have the purpose of developing an alternative method of pile loading tests. The presented monitoring technology proved itself as a very accurate and consistent. It gave in the first place the possibility of a closer look at the strains and stresses of the most unapproachable parts of different types of concrete structure elements especially piles and other types of deep foundations.
Ključne besede: piles, deep foundations, dynamic loading test, strain measurement technologies, elasto-plastic modelling, finite-element method
Objavljeno: 06.06.2018; Ogledov: 509; Prenosov: 48
.pdf Celotno besedilo (780,04 KB)
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Non-linear finite-element modelling of room and pillar mine workings including the strain-softening behaviour of the rock mass
Salim Bensehamdi, Abdelbaki Seriani, 2008, izvirni znanstveni članek

Opis: A two-dimensional model adopting post-failure criteria was used to simulate the behaviour of the rock mass and the development of yield zones around room and pillar mine workings. The model conformed to the strain-softening behaviour of the rock mass and accounted for its post-failure residual strength. The structural-stability-analysis approach accounted for the main features of the mine structures’ yield produced during loading through changes in the rock material’s stiffness and the subsequent evolution of the stresses. A comprehensive parametric analysis was performed and the inevitable effect of the interaction of the roof, pillar and floor on the overall stability limit of the mine was investigated. The numerical results clearly showed that the finite-element linear models could not realistically represent the true behaviour of the mine structure. However, they clearly demonstrated the limitations of the finite-element linear solutions in representing the true behaviour of the mine structure, particularly when the rock-mass structure is relatively weak, and that a non-linear approach was justified.
Ključne besede: non-linear FE analysis, yielding, plastic zones, room and pillar mining, residual strength, stability assessment
Objavljeno: 05.06.2018; Ogledov: 403; Prenosov: 41
.pdf Celotno besedilo (651,93 KB)
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A 3D nonlinear dynamic analysis of a rock-fill dam based on IZIIS software
Violeta 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: 922; Prenosov: 59
.pdf Celotno besedilo (923,69 KB)
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A multiscale approach to deformation and fracture of heat-resistant steel under static and cyclic loading
P. O. Maruščak, Denys Baran, Vladimir Gliha, 2013, izvirni znanstveni članek

Opis: Regularities of static and cyclic deformation, damage and fracture of heat-resistant steel 25Kh1M1F, based on the approaches of physical mesomechanics and 3D interferometry method, are presented in this paper. The applicability of these techniques for different hierarchy levels of deformation was studied. The investigation of scanning microscope photos was conducted for several dissipative structures, fragmentation of the material, localisation of macrodeformation and subsequent failure on macro- and mesolevel. It is shown that the used modern techniques of experimental analysis are very efficient in understanding deformation and damage evolution in materials.
Ključne besede: fracture, heat-resistant steel, cyclic loading, fatigue, plastic deformation
Objavljeno: 18.08.2017; Ogledov: 595; Prenosov: 273
.pdf Celotno besedilo (2,42 MB)
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Unobtrusive heartbeat monitoring by using a bed fiber-optic sensor
Peter Podbreznik, Denis Đonlagić, Dejan Lešnik, Boris Cigale, Damjan Zazula, 2014, izvirni znanstveni članek

Opis: Demographic trends suggest that by 2050 approximately 11 % of the world population will be 80 or older. If a fast increase of chronic diseases is also considered, it becomes clear the present healthcare capacities won't be enough. The elderly and people with limited abilities must be assisted in their home environment and, thus, reduce needs for hospitalization and institutionalization. Today's computer and communication technologies provide different smart devices, which is a core of emerging intensification of homecare services, in particular remote and unobtrusive monitoring of human functional- health parameters.
Ključne besede: plastic optical fiber, speckle interferometry, unobtrusive monitoring of human vital signs, heartbeat detection, ballistocardiography
Objavljeno: 21.12.2015; Ogledov: 853; Prenosov: 86
.pdf Celotno besedilo (573,53 KB)
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Unobtrusive monitoring of human vital functions based on speckle interferometry with plastic optical fiber
Peter Podbreznik, Denis Đonlagić, Dejan Lešnik, Boris Cigale, Damjan Zazula, 2013, izvirni znanstveni članek

Opis: In this paper, a speckle interferometer with a plastic optical fiber system is reported for unobtrusive monitoring of heartbeat and respiration. The sensor consists of a laser diode butt-coupled to the plastic optical fiber, whose exit face projects speckle patterns onto a linear optical sensor array, which leads to a simple and cost-effective construction. Speckle images are acquired in a sequence and transformed into a 1D signal by using a phase-shifting method. Band-pass filtering and Morlet-wavelet-based multiresolutional approaches were used to analyze signals for the detection of cardiac and respiratory activities, respectively. Ten young, healthy persons participated in system testing, by lying supine on a mattress with embedded plastic optical fiber. Experimental results show the proposed system and detection algorithms are highly efficient. Sensitivities of 99.4 0.6% and 95.3 3%, precisions of 98.8 1.5% and 97.9 2.3%, and mean delays between interferometric detections and corresponding referential signals of 116.6 55.5ms and 1299.2 437.3 ms were computed for heartbeat and respiration, respectively.
Ključne besede: plastic optical fiber, speckle interferometry, unobtrusive monitoring, heartbeat detection, respiration detection, phase-shift method, wavelet transform
Objavljeno: 10.07.2015; Ogledov: 900; Prenosov: 12
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