1,721,102 research outputs found
Numerical analysis of deformation and stability in the formation for railway tracks
Full text linkOver the past few decades, the increasing demands of railways operations in the form of heavy loading and high speed have been noticed. Railway formation and ballast deform progressive under heavy axle cyclic loading, therefore the rail track needs proper design of ballast and formation bed to achieve the desire stiffness and stability for the safe and sound serviceability of the track. For the overall stability of the track on soft formation, the ground is improved by different techniques prior to the construction on that, in order to avoid the failure and differential settlement during the designed trains operation.
The numerical analyses illustrate that the total deformation and bearing capacity of the railway tracks mostly depend on the changes in the friction angle and cohesion of the selected soils of the subgrade. To avoid failure in the formation of track under the design loads, the proper selection of types of soils, its layer thickness, well compaction during construction and provision of proper track drainage system are extremely important. For the construction of new railway tracks the soils having greater values of friction angle, cohesion and elastic stiffness with the well graded ballast cushion under the sleepers of designed side slopes can be used to reduce the maintenance cost, considerably increase the life time of the components of the tracks and ultimately give better performance of the tracks
Numerical Analysis of Soil Behavior and Stone Columns Effects on the Railway Track
Full text linkRailway systems are highly competitive compared with other means of transportation because of their distinct advantages in speed, convenience and safety. Therefore, the demand for railway transportation is increasing around the world. Constructing railway tracks and related engineering structures in areas with loose or soft cohesive subgrade usually leads to problems, such as excessive settlement, deformation and instability. Several remedies have been proposed to avoid or reduce such problems, including the replacement of soft soil and the construction of piles or stone columns. This thesis aims to expand the geotechnical knowledge of how to improve subgrade ballasted railway tracks, using stone columns and numerical modeling for the railway infrastructure. Three aspects are considered: i) railway track dynamics modeling and validation by field measurements, ii) modeling and parametric studies on stone columns, and iii) studies on the linear and non-linear behavior of stone columns under the dynamic load of trains. The first step of this research was to develop a reliable numerical model of a railway track. The finite element method in a time domain was used for either a 2D plane strain or 3D analysis. Individual methods for modeling a train load in 2D and 3D were implemented and are discussed in this thesis. The developed loading method was validated with three different railway tracks using obtained vibration measurements. Later, these numerical models were used to analyze the influence of stone column length and train speed in the stress field. The performance of the treated ground depends on various parameters, such as the strength of stone columns, spacing, length and diameter of the columns. Therefore, the second step was devoted to a parameter study of stone columns as a unit cell with an axisymmetric condition. The results showed that even short stone columns were effective for settlement reduction, and area of replacement was the main influential parameter in their performance. The third part of this thesis focuses on a hypothetical railway-track response to the passage of various train speeds and the influence of stone-column length. The stress-strain response of subgrade is analyzed under either an elastic–perfectly plastic or advanced constitutive model. The non-linear soil response in the finite element method and the impact of train speed and stone column length on railway tracks are also evaluated. Moreover, the reductions of induced vibration – in both a horizontal and a vertical direction – after improvement are investigated
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Contributions to the experimental investigation and numerical description of soil cyclic behavior
No full textA wide range of geotechnical structures are subjected to episodes of cyclic loading. Among them, we can for example mention onshore and offshore foundations subjected to environmental loadings, pavements subjected to traffic loading, filling-emptying cycles on silos and water tanks, among many others. In order to develop constitutive models or numerical tools that accurately reproduce the soil behavior on the aforementioned geotechnical problems, a deep understanding on how soil behaves under cyclic loading is necessary. This behavior is, however, not trivial since non-linearity, small strain stiffness, stiffness degradation, cyclic hysteresis and recent stress history play a significant role. This dissertation presents some contributions to the experimental evidence and numerical description of soil cyclic behavior. It begins with comprehensive experimental databases on Malaysian kaolin and Zbraslav sand. In each database, several monotonic and cyclic tests were performed and analyzed considering a wide range of initial conditions and loading characteristics. In particular, the influence of the deviatoric stress amplitude, soil plasticity, initial stress ratio, drained cyclic preloading and sequence of packages of cycles with different deviatoric stress amplitudes was investigated on Malaysian..
Parameter estimation for hypoplasticity via inverse analysis
No full textCohesionless soils show a complex stress-strain behavior that depends on the stress and strain state, the initial density and also on the stress history among other things. Many constitutive models are capable of modeling some of these aspects and only few models are able to take all this into account. The hypoplastic model developed by von Wolffersdorff (1996) is able to model all these aspects in a satisfactory manner for problems with monotonous loading and most importantly, all of this with one set of parameters. Unfortunately, a correct parameter estimation for this constitutive model represents a great challenge. The use of an inverse analysis to estimate the hypoplastic parameters can overcome most of the difficulties encountered by forward or “classical” parameter estimation. Therefore, efforts have been directed towards the implementation of such a technique for the hypoplastic model in question. The main objective of this implementation is to make the parameter estimation for the hypoplastic model a more accessible and reliable procedure. The first step performed in this implementation consisted of assessing the applicability of the parameter estimation via inverse analysis to this hypoplastic model. Therefore, synthetic data were used as reference data for the parameter estimation via inverse analysis. This allowed not only a pure evaluation of the inverse analysis (without external factors or uncertainties in the reference data) but also an identification of the required experimental data for a proper parameter estimation.As a second step, the information obtained was applied to design an experimental program. This required the design, construction and calibration of a new device that allowed the attainment of the required experimental data. Only then the inverse analysis implementation could be successfully tested using real soil data. An optimal set of parameters was obtained for the different cohensionless soils. The results obtained suggested that the parameters obtained using the inverse analysis were able to describe the measured data in a good manner. As a third and last step, the newly obtained parameters were validated by calculating different laboratory tests. These tests were selected in such a way that both the sample preparation as well as the boundary conditions differ with the ones used for the parameter estimation. The simulations showed a good agreement with the laboratory results
Příspěvky k experimentálnímu zkoumání a numerickému popisu cyklického chování zemin
Full text linkŠiroká škála geotechnických konstrukcí je vystavena epizodám cyklického zatížení. Mezi nimi můžeme zmínit například základy na pevnině a na moři vystavené zatížení od prostředí, chodníky vystavené dopravnímu zatížení, cykly plnění a vyprazdňování sil a vodních nádrží a mnoho dalších. Pro vývoj konstitutivních modelů nebo numerických nástrojů, které přesně reprodukují chování zeminy při výše uvedených geotechnických problémech, je nutné hluboké porozumění tomu, jak se zemina chová při cyklickém zatížení. Toto chování však není triviální, protože významnou roli hraje nelinearita, tuhost při malých deformačních změnách, degradace tuhosti, cyklická hystereze a nedávná historie napětí. Tato disertační práce představuje některé příspěvky k experimentálním důkazům a numerickému popisu cyklického chování půdy. Začíná rozsáhlou experimentální databází malajského kaolinu a zbraslavského písku. V každé databázi bylo provedeno a analyzováno několik monotónních a cyklických zkoušek s ohledem na širokou škálu počátečních podmínek a zatěžovacích charakteristik. Na malajském kaolinu byl zkoumán zejména vliv amplitudy deviatorického napětí, plasticity zeminy, počátečního poměru napětí, odvodněného cyklického předpětí a posloupnosti balíčků cyklů s různými amplitudami deviatorického napětí. Na zbraslavském písku byl...A wide range of geotechnical structures are subjected to episodes of cyclic loading. Among them, we can for example mention onshore and offshore foundations subjected to environmental loadings, pavements subjected to traffic loading, filling-emptying cycles on silos and water tanks, among many others. In order to develop constitutive models or numerical tools that accurately reproduce the soil behavior on the aforementioned geotechnical problems, a deep understanding on how soil behaves under cyclic loading is necessary. This behavior is, however, not trivial since non-linearity, small strain stiffness, stiffness degradation, cyclic hysteresis and recent stress history play a significant role. This dissertation presents some contributions to the experimental evidence and numerical description of soil cyclic behavior. It begins with comprehensive experimental databases on Malaysian kaolin and Zbraslav sand. In each database, several monotonic and cyclic tests were performed and analyzed considering a wide range of initial conditions and loading characteristics. In particular, the influence of the deviatoric stress amplitude, soil plasticity, initial stress ratio, drained cyclic preloading and sequence of packages of cycles with different deviatoric stress amplitudes was investigated on Malaysian...Institute of Hydrogeology, Engineering Geology and Applied GeophysicsÚstav hydrogeologie, inženýrské geologie a užité geofyzikyFaculty of SciencePřírodovědecká fakult
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Soil behaviour under cyclic loading - experimental observations, constitutive description and applications
No full text- …
