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GNSS monitoring of geologically demanding areas
Boštjan Kovačič, Boško Pribičević, Rok Kamnik, 2016, izvirni znanstveni članek

Opis: Displacement research using the three-dimensional global navigation satellite system (GNSS) as part of geodetic monitoring is becoming the key investigation for establishing a cause-and-effect relationships model between external natural factors, on the one hand, and the criteria that describes the level of functionality and safety of the observed natural or artificial object, on the other, in cases of motion of an object in space and time. The main objective of the deformation analysis is to confirm the stabilities of the reference points of a geodetic network, which are used to determine the movements of the control points that are stabilized on the observed objects. The assumption about the stabilities of certain reference points must be based on reasonable grounds, underpinned by measurements and proven by numerical methods. This is one part of the results of the deformation analysis when determining the extent of the movements and deformations. To do this a transformation is used in which a comparison is made between the coordinates of the points for two separate epochs. On the basis of the estimated transformation parameters, possible movements can be concluded within the reference points, i.e., on whether the datum parameters have changed. After confirming the stability of the geodetic network the coordinate differences of identical points measured within the different time windows can be determined as displacements and/or deformations of an object. In this paper one viaduct was assessed through geology and tectonic activities and also a load test of the viaduct was performed. The viaduct is in a quite active region, but the load test showed that the bridge response to the load is as expected.
Ključne besede: geodesy, geotehnics, monitoring, GNSS measurements, geology, deformation analysis, geodetic network
Objavljeno: 18.06.2018; Ogledov: 4; Prenosov: 0
.pdf Celotno besedilo (630,78 KB)

Modeling of a geocell-reinforced pavement
Samo Peter Medved, Bojan Žlender, Stanislav Lenart, Primož Jelušič, 2016, izvirni znanstveni članek

Opis: This article details how the serviceability of a flexural pavement structure is improved by incorporating the Cellular Confinement System (geocells). For this purpose, two different pavement structures, with and without embedded geocells, were manufactured in a laboratory and an accelerated traffic type of loading was applied. The vertical and horizontal cyclic loads were applied simultaneously to simulate the effect of principal stress rotation. A comparative study between the conventional flexible pavement and the geocell-reinforced flexible pavement is presented. Additionally, numerical models of the laboratory tests were built and the results were compared. The simulation of the experimental tests using the Traffic Load Simulator (TLS) are carried out using the FEM and advanced models that describe the permanent strain behavior of the unbound granular material. The development of permanent deformation within the pavement structure, with and without the geocells, is also presented through the numerical model, which was verified by the experimental results.
Ključne besede: flexible pavement, reinforcement, geocell, traffic load simulator, permanent deformation, numerical modeling
Objavljeno: 18.06.2018; Ogledov: 8; Prenosov: 0
.pdf Celotno besedilo (1,39 MB)

Use of a Perth sand penetrometer (PSP) device to determine the engineering parameters of sands
S. D. Mohammadi, 2016, izvirni znanstveni članek

Opis: Determining the in-situ engineering parameters of sandy soils has always been a challenge for geotechnical engineers, resulting in several methods having been developed so far. The Perth Sand Penetrometer (PSP) test is one of the most versatile of these methods. It is a considerably faster and cheaper tool than boring equipment, especially when the depth of the exploration is moderate. In the present research, a methodology for the use of a PSP device to evaluate the engineering parameters of sandy soils in laboratory conditions is discussed and the repeatability of the test results is studied. First of all, the tests were performed on typical Tehran young alluvial deposits (poorly graded sandy soil, SP) consistently prepared to 5 densities using the sand raining or pluviation technique. Next, the normal and logNormal distributions of the test data using the Kolmogorov-Smirnov normality test were examined. After that, based on the obtained results, the relationship types between the dynamic point resistance index (qd) and other parameters, such as the relative density (Dr), the modulus of elasticity (E), the shear modulus (G) and the friction angle of the soil, were determined. The results show that the obtained relationships were semi-logarithmic and logarithmic, and most of the obtained experimental formulas had a high coefficient of determination (>90%). To evaluate the accuracy of the results, 95% confidence and prediction bands were also used and the results show that all the obtained experimental relationships were appropriate. Finally, the repeatability of the test results was evaluated by calculating the coefficient of variations, which was less than 30% for all the tests.
Ključne besede: dynamic-point resistance index (qd), engineering parameters, repeatability, statistical methods
Objavljeno: 18.06.2018; Ogledov: 3; Prenosov: 0
.pdf Celotno besedilo (580,07 KB)

A method for predicting the deformation of swelling clay soils and designing shallow foundations that are subjected to uplifting
Baheddi Mohamed, Djafarov Mekhti, Charif Abdelhamid, 2016, izvirni znanstveni članek

Opis: Swelling soils can be found in many parts of the world. The state of practice in this area has been changing over recent decades. The design of foundations for expansive soils is an impo rtant challenge facing engineers. The excessive damage is, in part, due to the lack of proper design, resulting in the need for better tools for practitioners in order to assess the impact of swelling soils in typical design applications. A correct measurement of the swelling pressure is required for an accurate prediction of the heave. A theoretical model is proposed to describe the swelling potential of clay soils on the basis of their characteristics obtained from oedometer tests. This paper describes analysis of the behavior of swelling soils when moistened under buildings and structures. The methods and principles currently used for the design of structure foundations on swelling soils involve important problems due to the non-uniform deformations of these soils when subjected to structural loads. The current study was conducted to compute the uplifting of shallow foundations on swelling soils considering the water-content change as well as the contact-pressure distribution under the footing.
Ključne besede: swelling soil, swelling magnitude, swelling pressure, free-swell oedometer test, loaded-swell oedometer test, shallow foundations
Objavljeno: 18.06.2018; Ogledov: 5; Prenosov: 0
.pdf Celotno besedilo (465,96 KB)

Performance of soilnailed and anchored walls based on fieldmonitoring data in different soil conditions in Istanbul
Dogan Çetin, 2016, izvirni znanstveni članek

Opis: In this study, data on the lateral wall displacements of 28 deep excavations in Istanbul soil from over 90 field monitors were collected and analysed. The most commonly used retaining walls for deep excavations in Istanbul are soil-nailed shotcrete walls (SNPWs) and contiguous pile walls (CPWs). Other types of retaining walls include anchored micropile walls (MPWs), diaphragm walls (DWs), concrete walls (CWs) and secantpile walls (SPWs). The analyses were performed under two main headings: analysis of soil-nailed walls’ data and analysis of anchored walls’ data. The data of δh,max generally range from 0.05%H to 0.35%H with an average value of 0.20%H in the soil-nailed projects. The data of δh,max generally range from 0.043%H to 0.32%H with an average value of 0.155%H in anchored pile wall projects. Some factors affecting the deformation of deep excavations, such as nail density, embedded wall ratio and wall stiffness, were studied based on field-monitoring data. Wall movements were also compared with observations in some case histories from around the world.
Ključne besede: deep excavation, wall displacement, soil formation, soilnailed wall, anchored wall
Objavljeno: 18.06.2018; Ogledov: 6; Prenosov: 0
.pdf Celotno besedilo (483,16 KB)

A fundamental study of the performance of X-section cast-in-place concrete single piles
Yu Wang, Yaru Lv, Dongdong Zhang, Jieying Zhou, 2016, izvirni znanstveni članek

Opis: X-section cast-in-place concrete (XCC) piles are used because they have a higher bearing capacity than circularsection cast-in-place concrete (CCC) piles of the same cross-sectional area. Although the bearing capacity of XCC piles has been studied, the performance of XCC single piles, especially for the stress-transfer mechanism dependent on the geometrical effects, is still not fully understood. This paper reports two comparative field static load tests on an XCC and a CCC single pile of the same cross-sectional area. In addition, corresponding threedimensional numerical back-analyses are performed to provide a fundamental understanding. The measured and computed results reveal that the XCC single pile has an approximately 25% higher ultimate bearing capacity than the CCC single pile. This is because the XCC single pile has an approximately 20% larger total side resistance, which is caused by a 60% larger pile perimeter and a slightly smaller unit side resistance. Lateral soil arching effects are developed, causing a non-uniform effective normal stress and a shear stress across the circumference of the XCC single pile. It is suggested that XCC single piles have a higher efficiency in terms of material saving compared with CCC single piles.
Ključne besede: X-section cast-in-place concrete pile, field static load test, three-dimensional numerical back-analysis, stresstransfer mechanism, side resistance, soil arching
Objavljeno: 15.06.2018; Ogledov: 94; Prenosov: 0
.pdf Celotno besedilo (485,57 KB)

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: 100; Prenosov: 1
.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: 95; Prenosov: 1
.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: 91; Prenosov: 0
.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: 93; Prenosov: 0
.pdf Celotno besedilo (305,84 KB)

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