CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)
Not a member yet
4735 research outputs found
Sort by
Extracting general knowledge of model parameters for clays out of numerous laboratory tests
Get PDFThis paper is concerned with the process of determining the material parameters of advanced constitutive models for clays. Provided results are applicable already in the early stages of geotechnical survey when no detailed data from laboratory tests of soils expected at construction site are known. A worldwide database of laboratory tests obtained during four year operation of web calibration application ExCalibre was used for this purpose. This application allows automatic calibration of three advanced constitutive soil models based on detailed data from triaxial and edometric tests. The paper describes the process of determining the confidence intervals of each material parameter of modified Cam-clay and hypoplastic clay models for low (CL) and high (CH) plasticity clay according to unified soil classification system (USCS) and tabulates their typical ranges. The purpose of presented work was to contribute to the use of advanced constitutive models among practical engineers
Return mapping scheme for the Hoek-Brown model with tension cut-off
Get PDFThe present paper revisits a stress update procedure for the Hoek-Brown plasticity model enhanced by a Rankine type of tension cut-off failure criterion. Limiting tensile stresses not only supports the behavior of weak rock masses with a very low tensile strength but in combination with the original Hoek-Brown model improves robustness of the stress update procedure, i.e. the stress return mapping algorithm. Herein, the primary focus is on the stress return from a space of inadmissible trial stresses for which neither the Hoek-Brown yield surface nor its derivative can be evaluated. All potential scenarios are thoroughly discussed both in the framework of single- and multi-surface plasticity. The presented procedures were implemented and verified with the help of the Geo5 FEM software
Linearisation of a second-order nonlinear ordinary differential equation
Get PDFWe analyse nonlinear second-order differential equations in terms of algebraic properties by reducing a nonlinear partial differential equation to a nonlinear second-order ordinary differential equation via the point symmetry f(v)∂v. The eight Lie point symmetries obtained for the second-order ordinary differential equation is of maximal number and a representation of the sl(3,R) algebra. We extend this analysis to a more general nonlinear second-order differential equation and we obtain similar interesting algebraic properties
Considerations on an embedded pile’s effective length in an analytical calculation according to the commentary on the STN 73 1002 standard
Get PDFThe analytical model for calculating the bearing capacity of a pile, presented in the commentary to STN 73 1002 – Pile Foundations, gives a recommendation to reduce the pile’s length in the calculation of the shaft resistance. The recommendation is based on Caquot-Kérisel’s theory. Especially in the case of embedded piles, reducing a pile’s length in the calculation can cause the shaft friction of the embedded pile to be neglected, and the calculated resistance of the pile is thus significantly lower. The results of instrumented static load tests of embedded piles were analysed. The main aim of the study was to verify the validity of reducing the pile’s length in the analytical calculation of the shaft resistance. The results of the static load tests analysed did not show any reduction in the shaft friction on the embedded part of the pile. In the form of a parametric study, the effect of reducing the pile’s length in the calculation of shaft friction was analysed for different dimensions of embedded piles
Earth structures – a summary of the last 50 years
Get PDFThis paper discusses changes and developments in the field of Earth Structures that have been presented and discussed over the last fifty years at the annual national conferences on Foundation Engineering held (with foreign participation) in the city of Brno
SAFETY ASSESSMENT OF CONTINUOUS CONCRETE GIRDER BRIDGES SUBJECTED TO RANDOM TRAFFIC LOADS CONSIDERING FLEXURAL-SHEAR COUPLED FAILURE
No full textBridges generally perform complicated mechanical behaviors under external loads, such as flexural-shear coupling, compression-bending coupling, and flexural-shear-torsion coupling. In the context of deterministic design approaches such as design codes, these complicated coupled issues are generally simplified to the safety verification of bridge components under a single mechanical state (i.e. flexural, shear, torsion). At present, the rapid development of sensor and information technologies makes it possible to collect the external loads acted on bridges and understand bridge performance under these stochastic external loads. In this manner, the reliability-based full probabilistic approach could be applied to investigate the performance of bridges over their lifetime. However, the current bridge reliability assessment incorporating realistic traffic load measurements mainly focuses on the analysis of bridge components under a single mechanical state. In this paper, a reliability-based probabilistic analytical framework of the flexural-shear performance of girder bridges under random traffic loading is established. The flexural-shear coupled failure path of bridge girders under random traffic loading is characterized for the first time, where the bivariate extreme value theory is incorporated to develop the extreme value distribution of combined flexural and shear load effects. The modified compression field theory recommended by AASHTO is employed to establish the coupled flexural-shear coupling resistances. Finally, the reliability of the flexural-shear performance of bridge girders is evaluated by solving the multivariate ultimate limit state equation. The proposed analytical framework is applied to a realistic bridge. The results show that the reliability index of the flexural-shear coupling evaluation is lower than that of the flexural or shear evaluation, which highlights the importance of the flexural-shear performance checking in the reliability assessment of bridges under random traffic loading. The proposed analytical framework could be further applied to the probabilistic assessment of bridge components subjected to combined loading mechanisms under random loadings
Experience with sleeper substructure design for a speed of 200 kph according to the S4 standard
Get PDFThe paper deals with the sleeper substructure design for a speed of 200 kph according to the Czech SŽ S4 standard. The paper includes the design of sub-ballast and capping layers. The second part of the paper is focused on transition area design. The conclusion brings recommendations of alterations which would be appropriate to incorporate into the standard
Artificial intelligence in operational applications of railway infrastructure manager
Get PDFThe main goal of this article is to present the possibility of using artificial intelligence in operational application of railway infrastructure manager. Railway 4.0 can be controlled fully digitally – operational applications based on the artificial intelligence can optimize the technology of railway traffic control. Thereafter, a wide range of equipment could be controlled by application through a secure interface
Recycled materials for sublayers
Get PDFThe article focuses on the recycled materials used in sleeper substructure. In the introduction, it summarizes the requirements for bearing layers of railway substructure and recycling of waste construction materials. The article presents the materials on which laboratory tests have been carried out and discusses in detail the most perspective – recycled concrete. For concrete recyclate, the article describes the results of laboratory tests – sieve analysis, determination of optimum moisture, and determination of bearing capacity using California bearing ratio, Immediate bearing index and Static deformation modulus
Directing classical geotechnical engineering to future challenges
Get PDFGeotechnical engineers have traditionally been focused on soil mechanics, rock mechanics and engineering geology. Thus it has been sufficient to master these topics to be recognized as a key participant in building and civil engineering projects. However, gradually concerns within both projects themselves and societies more generally are shifting towards new questions and challenges. Therefore, ensuring that geotechnical engineers remain central to all relevant projects, there is a need to master increasingly different and new ways of working together, obtaining new skills and increasing professionally pertinent knowledge and experience. This paper will give an overview of the issues geotechnical engineers have to address and master, if they are to take a lead in projects that seek to meet future challenges. This is really about working in a multi-disciplinary environment, using relevant technical methods without losing specifically engineering judgement, and then using open-minded communication skills to question previous practices that can proceed to find solutions to those future challenges identified. How is this to be done successfully within the profession? This paper offers some ideas. All professionals, and geotechnical engineers cannot be an exception, want to influence and contribute to solving current and future challenges, and thus we need to expand our knowledge awareness. The list of topics where we need to develop our knowledge is rather lengthy and include environmental considerations, contracts, law, conceptualisations of sustainability, robustness, monitoring, digitalisation, standardisation, and climate change. This paper will highlight two examples where geotechnical engineers with increased knowledge sensitivity and skills could make a significant contribution. First, there is an example from Göteborg about limiting a project impact within its zone of influence. Designing the geotechnical structure itself is only the first step, for in addition there is a need to control the building process, have sufficient monitoring, handling the expectations of society while ensuring recognition and use of a particular professional scope of operation. The other example concerns the re-use of material in our embankments to limit transportation. Which criteria should be used to determine the suitability of materials for re-use? How can we cope with societal reactions? Finally, the paper will discuss how geotechnical engineers, by combining geotechnical knowledge with new skills, can contribute with a sustainability foundation involving both relevant concepts and principles looking forward