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The geo-mechanics behaviour of soft marine silts under a nearshore rubble-mound breakwater
Lien-Kwei Chien, Feng Tsung-Shen, Tsung-Ching Chen, 2009, original scientific article

Abstract: In this study, the soft marine silts under a rubble-mound breakwater in Ma-Zu of west Taiwan are adopted as a test sample. The specimens were prepared by a new, remolded method at dry density and consolidated stresses. Tri-axial shear-strength tests were performed to evaluate the pore-water pressure and the shear strength. The test results show that the pore-water pressure increases gradually and is close to the critical values as the axial strain increases. In addition, under isotropic and K0 consolidation, both the c and c' of the soft marine silts were 0 kPa, which means that the silts do not have any shear resistance, just like fluid under a rubble-mound breakwater. Based on the linear-elasticity and the one-dimensional consolidation theory, the model of the settlement and stability was evaluated in SIGMA/W. The results show that the soft marine silts at the breakwater induced a displacement, greatly increasing with the filling rubble-mound loading. The figures and results can be referenced for a stability evaluation of the silt soil deposits under the rubble-mound breakwater. The results are useful for marine silts mechanics and a stability analysis for the planning, design, and related research on near-shore engineering.
Keywords: geo-mechanics behavior, soft marine silt, rubble-mound breakwater, settlement, numerical simulation mode
Published: 06.06.2018; Views: 559; Downloads: 46
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Determination of passive earth pressure using three-dimensional failure mechanism
Helena Vrecl-Kojc, Stanislav Škrabl, 2007, original scientific article

Abstract: 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.
Keywords: soil mechanics, passive earth pressure, upper bound theorem, optimization, three-dimensional failure mechanism
Published: 18.05.2018; Views: 462; Downloads: 34
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Probing ion dynamics in a clay-water system with dielectric spectroscopy
Marko Samec, Dean Korošak, Bruno Cvikl, 2007, original scientific article

Abstract: Dielectric spectroscopy characterization of clay-water mixtures is presented and the obtained spectra are analysed. A theoretical model for ion dynamics isproposed in which motion of ions in pore space electrolyte is interrupted by trapping events at the mineral surfaces. The typical time scales for these processes are given in terms of the physical properties of the material. It isshown that the microscopic motion of the ions in a complex environment of clay-water system can be described with fractional dynamics leading to subdiffusive behavior.
Keywords: soil mechanics, dielectric spectroscopy, porous material, conductivity, fractional dynamics
Published: 18.05.2018; Views: 405; Downloads: 62
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Mean grain size as a function of spectral amplitude: a new regression law for marine sediment cores
Nelly Zanette, Darinka Battelino, 2017, original scientific article

Abstract: Geophysics has been developed in order to supply indicative estimations in soil mechanics like the grain size distribution of finely grained soils as day, silt and fine sands. The paper describes the attempt to characterize porous and saturated marine sediments with a non destructive technique which is the acoustic wave, in order to determine the correlation with geotechnical measurements. The characterization of physical parameters of marine sediments was based on research methods which permit to describe the parameters defining different types of sediment and zones of sedimentation; to determine fundamental parameters that influence the propagation of the acoustic waves in saturated and porous means; to define quick and indicative methods for characterization of physical parameters of analysed means. The acoustic measurements were carried out at SACLANT-NATO of La Spezia (I), where the Vertical Multi Sensor Core Logger (V-MSCL) was used. The results of acoustic tests were compared to the grain size curves of the sediments and the propagation characteristics such as velocity, density, porosity and absorption of experimentally determined data. The analyses are based 011 various mathematical models presented in. literature, in order to predict and to describe physical mechanisms of the wave propagation using a simplification of the sediment structure. The target of the study was to determine a new mathematical law that linked the mean grain size to a directly measurable parameter such as the spectral amplitude, and to offer the possibility to obtain the first indicative value of the sediment mean grain size. The determined exponential law represents an innovative and quick approach to determine a physical characteristic of saturated and porous sediments such as the grain size in a non destructive way based on the spectral analysis of the wave propagation form.
Keywords: soil mechanics, marine sediments, finely grained soil, acoustic waves, grain size curve
Published: 17.05.2018; Views: 496; Downloads: 52
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The assesment of pile shaft resistance based on axial strain measurements during the loading test
Andrej Štrukelj, Stanislav Škrabl, Ksenija Štern, Janko Logar, 2005, original scientific article

Abstract: Near Maribor, a new bridge over the Drava river is being under construction. Before the main works actually started, static and dynamic loading tests of piles were performed. The goal of the static loading test was to determine the bearing capacitiy of the test pile. It was also interesting to determine the share of the axial load distributed on the shaft and pile toe. In order to measure the distribution of the axial force along the pile, a specially made steel canal was built in the pile before concreting. Inside this canal the strain gauges were distributed evenly at the distance of one meter. The strains were measured for each loading phase in all measuring points. The distribution of the axial force was assessed from the obtained results and based on the distribution of the axial force the shaft resistance could be determined. The unexpectedly high bearing capacity of the pile shaft made the obtained results highly interesting. In this paper, measuring methods and measuring results are discussed. Behaviour of the pile and the soil during the loading test were also modelled by axial symmetric and three dimensional models. The calculated and measured results show a very good agreement.
Keywords: civil engineering, bridges, soil mechanics, pile shaft resistance, loading test, strain measurements, elastoplastic soil modelling, finite element method
Published: 16.05.2018; Views: 628; Downloads: 36
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Undrained shear strength of saturated cohesive soils depending on consolidation pressure and mineralogical properties
Bojana Dolinar, 2004, original scientific article

Abstract: The relationship between the water content and the undrained shear strength of finely grained soils can be described with a nonlinear function in which the type of soils is determined by two parameters. These parameters depend primarily on the size of clay minerals, their quantity in soil composition and the interlayer water quantity in expanding clay minerals. This article asserts that there exists also the exactly defined relationship also between the water content and consolidation pressure. In the function describing this relationship, the type of soil is determined by two parameters. They can be expressed depending on the same mineralogical properties of soils as the values of parameters in the function showing the relationship between the water content and the undrained shear strength. These findings allow us to express the ratio between undrained shear strength and consolidation pressure depending on mineralogical properties of soils.
Keywords: soil mechanics, properties of soils, clays, specific surface, undrained shear strenght, compressibility
Published: 15.05.2018; Views: 610; Downloads: 66
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Experimental determination of fatigue parameters of high chromium steel under different loading and temperature conditions
Matej Drobne, Nenad Gubeljak, Srečko Glodež, 2014, original scientific article

Abstract: Fatigue investigation of high chromium steel (HCS) at different loading ratios (R = 0, R = -1) and different temperatures (20 °C, 600 °C) is presented in this paper. Before fatigue testing, monotonic mechanical properties (ultimate compressive and ultimate tensile strength) are determined at different temperatures, using standardized testing procedures according to DIN 50125 standard. Moreover Charpy impact tests at different temperatures were done with specimens that comply with the standard ISO 14556. Fatigue testing is performed on a servo - hydraulic testing machine with consideration of different loading conditions as described above. On the basis of the experimental results the S - N curves are constructed from which typical fatigue parameters (the fatigue strength coefficient 0'f and the fatigue strength exponent b) are determined. After fatigue testing a comprehensive investigation of fracture surfaces is performed using the Scanning Electron Microscope (SEM). Experimental results presented in this paper will serve as a basis for further investigations related to fatigue behaviour of real working rolls in hot strip mills made of HCS.
Keywords: experiments, high chromium steel, high cycle fatigue, fracture mechanics
Published: 12.07.2017; Views: 497; Downloads: 99
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Fatigue crack growth and fracture mechanics analysis of a working roll surface layer material
Matej Drobne, Tomaž Vuherer, Ivan Samardžić, Srečko Glodež, 2014, original scientific article

Abstract: Fatigue crack growth and fracture mechanics analysis of a working roll surface layer material is presented in this paper. The research is done on a hot strip mill working roll where High Chromium Steel is used for roll’s shell material. To obtain corresponding parameters, a rectangular single edge notched bend specimens – SENB, according to standard BS 7448, were used. The fatigue crack growth analysis was done on a resonant testing machine with use of special crack gauges, while for fracture mechanics parameters the electro–mechanical testing machine was used.
Keywords: fracture mechanics, fatigue crack growth, metal forming, rolling process, high chromium steel
Published: 03.07.2017; Views: 476; Downloads: 80
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Factors influencing the yielding constraint by cracked welded components
Dražan Kozak, Jelena Vojvodič-Tuma, Nenad Gubeljak, Damir Semenski, 2005, original scientific article

Abstract: The effect of strength mismatch for welded joints performed with different geometries on the yielding constraint has been investigated in the context of single-edged fracture-toughness specimens subjected to bending SE(B) using the finite-element method. The crack was located in the centre of the weld. Two geometri cal parameters have been identified as being the most important: the crack-Iength ratio a/W and the sIenderness of the welded joint (W-a)/H. They were systematically varied as follows: a/W = 0.1; 0.2; 0.3; 0.4; 0.5 and W = 2H, 4H, 8H, 16H, 24H. Basic equations and plane-strain finite-element solutions for the overmatched SE(B) specimen with all configuration combinations are given. The results are in good agreement with those in literature. This paper aims to establish yield-Ioad solutions for the same weldment configurations, but with materials dissimilarity present within the weld. This situation is usually encountered during repair welding. For this purpose, a practical combination of filler materials, with the same portion of overmatched part with M = 1.19 and undermatched part with M = 0.86, has been selected. Plane-strain solutions for the heterogeneous weld with the cracklocated in the overmatched half were obtained. The influence of the yielding-constraint key parameters has al so been evaluated. Yield-Ioad results for the specimens performed with different weld widths have the greatest scattering for the a/W = 0.5. The transition from the overmatched to the undermatched solution with increasing H is evident. On the other hand, the behaviour of the specimen with a shallow crack is dictated by the overmatch region ahead of the crack tip and depends very little on the weld slenderness. An approximated 3-D area of the yield-Ioad solutions depending ona/W and (W-a)lH has been proposed. Furthermore, the stress triaxility parameter h has been calculated using 2-D and 3-D finite-element analysis, and given as a field in the spec imen to get an insight into yielding-constraint regions. It was found that the 3-D yield-Ioad solutions are very close to the plane-strain solutions. Also, the effect of a/W on the yielding constraint is more significant than the effect of Mand (W-a)/H.
Keywords: welded structures, welded joints, fracture mechanics, cracks, SE(B) specimens, yielding load, yielding constraint parameters
Published: 06.04.2017; Views: 818; Downloads: 67
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Fracture toughness of a high-strength low-alloy steel weldment
Jelena Vojvodič-Tuma, Nenad Gubeljak, Borivoj Šuštaršič, Borut Bundara, 2006, original scientific article

Abstract: The use of high-strength low-alloy steels for high-performance structures, e.g., pressure vessels and pipelines, requires often high-strength consumables to produce an overmatched welded joint. This globally overmatched welded joint contains local mis-matched regions, which can affect the unstable fracture behaviour of the welded joint and the welded structure itself. If local mis-matched regions are present in the vicinity of a crack tip, then the fracture toughness of the weld metal can be significantly lower than that of the base metal. In this paper, the influence of the weld-metal microstructure on the fracture behaviour is estimated enabling an evaluation of the resistance to stable crack growth through different microstructures. The lower bound of the fracture toughness for different microstructures was evaluated using a modified Weibull distribution. The results, obtained using specimens with a through thickness crack front, indicated a low fracture toughness, caused by the strength mis-matching interaction along the crack front. In the case of through-the-thickness specimens, at least one local brittle zone (LBZ) or a local soft region is incorporated into the process zone in the vicinity of the crack tip. Hence, an unstable fracture occurred with small stable crack propagation, or without it. Despite the fact that the differences between the impact toughness of the weld metal and the base metal can be insignificant, the fracture toughness of a weld metal can be significantly lower.
Keywords: fracture mechanics, welded joint, crack-tip opening displacement, resistance curves
Published: 16.03.2017; Views: 620; Downloads: 61
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