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Accounting for a spatial and experimental variability in numerical modelling of geotechnical structures
Kupa, Ondřej ; Mašín, David (advisor) ; Janda, Tomáš (referee)
This diploma thesis is focused on evaluation of influence of spatial and experimental variability of input data in numerical simulations of behaviour of geotechnical structures. Thanks to opportunity to use data source of sand from the only one location in order to evaluate spatial and experimental variability, the assessment was carried out using extracting the experimental uncertainty from the total spatial variability method. Primarily, an influence of different level of considered experimental variability on total response of material environment was investigated. Random field theory was used to model variabilities in parameters of geological underlay and Mohr-Coulomb ideal plastic constitutive soil model was taken into account. In order to achieve representative quantity of values for statistical quantification of resulting influence of considered variability level, Monte Carlo method was used. Presented method of extracting the experimental uncertainty from the total variability was verified on two geotechnical cases. First, a settlement of strip footing was solved. An increasing accuracy of settlement values depending on level of considered experimental variability was demonstrated. The second case was focused on assessment of variability influence on slope stability. In addition, a nonzero...
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Development of calibration methods for hypoplastic models
Šula, Igor ; Mašín, David (advisor) ; Janda, Tomáš (referee)
The calibration application named ExCalibre was developed at Technical University in Prague, Faculty of Civil Engineering. This application can automatically process experimental data and create set of parameters of hypoplastic models which are designed for saturated clays or sands. The aim of this master thesis was to support development of application for calibration with testing it on real experimental data sets. Automatic calibration of these data sets was compared with calibration by hand for identical data. The development of the application and main phase of testing took place in two stages, where the main calibration errors of calibration application were identified. After the final testing of application where the minor bugs and errors were overcome a user-friendly web application (soilmodel.com/excalibre/) was introduced. This final testing has gone beyond this thesis. The results from the main phases of testing are discussed in this thesis as well as the description of database of fine-grained and coarse-grained samples which were used to testing of application. Knowing the calibration of the model is crucial for its using, you can find description of the used constitutive models in this thesis, which are used in the calibration application, as well as a description of procedure for...
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Application of probabilistic methods in geomechanics
Suchomel, Radek ; Mašín, David (advisor) ; Šejnoha, Jiří (referee) ; Pruška, Jan (referee)
Three probabilistic methods of different complexity for slope stability calculations are in this work evaluated with respect to a well-documented case study of slope failure in Lodalen, Norway. A finite element method considering spatial random fields of uncorrelated parameters cohesion and friction angle is taken as a reference for comparison with two simpler methods based on Taylor series expansion, known as first-order-second-moment methods. It is shown that the FOSM method enhanced by a reduction of variance of input parameters due to spatial averaging along the potential failure surface leads to a significant improvement in predictions. This method is computationally inexpensive and can be used in combination with any existing finite element code, it is thus a useful approximate probabilistic method for geotechnical practice. Several limitations of the extended method for calculating probability of a slope failure are identified. An advanced hypoplastic constitutive model is used in probabilistic analyses of a typical geotech- nical problem, strip footing. The model, including horizontal and vertical correlation lengths, was calibrated using a set of experimental data on sand from horizontally stratified deposit. Some parameters followed normal, whereas other followed lognormal distributions....
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Modelling of soil asymptotic behaviour using discrete element method
Jerman, Jan ; Mašín, David (advisor) ; Boháč, Jan (referee)
Aim of this study is to characterize asymptotic states of particulate materials, including states in extension. Asymptotic states are defined as states reached after a sufficiently long stretching with a constant direction of the strain rate. They are attractors in the behaviour of granular material and they are reached independetly of the initial state. Discerete element method is used in the simulations, where the influence of strain rate direction on the final state is studied. Results for strain rate direction higher than 0 obtained by Mašín (2012a) are then compared with results for strain rate direction lower than 0. These sets of results coincide qualitatevely.
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Advantages and disadvatages of a hypoplastic model when used in modelling of deep excavations
Jelenová, Věra ; Mašín, David (advisor) ; Najser, Jan (referee)
In building construction, it is important to know in advance how the ground will behave in an area around an excavation. To do this we use numerical models, which predict the behavior of soils. There are many numerical models that more or less precisely predict the behavior of soils. In this thesis I will focus mainly on the hypoplastic model. It predicts the behaviour of soils well. The model has also several disadvantages, especially while predicting stress paths at small strain. I will then also describe an improved hypoplastic model, which clarifies the predictions of the soils behaviour. This thesis is created mainly as a core for a diploma thesis, which should focus on modeling of the soils behaviour, the improved hypoplastic model and excavation near the Bodam lake. This excavation was already a subjekt of a diploma thesis (Becker, 2009), but there only the original hypoplastic model was used. This thesis focuses on the description of some aspects of the mechanical soils behavior. The describtion of the original and the improved hypoplastic model and their parameters follows. In the other part of this thesis we describe the selected buiding projects of excavations in fine-grained soils.
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Contributions to the experimental investigation and numerical description of soil cyclic behavior
Duque Felfle, Jose Alejandro ; Mašín, David (advisor) ; Herle, Ivo (referee) ; Wichtmann, Torsten (referee)
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...
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Experimental investigation of shear strength of soils from the Dobkovičky landslide area and development of correlations between soil strength and their physical properties
Roháč, Jakub ; Mašín, David (advisor) ; Blahůt, Jan (referee) ; Hrubešová, Eva (referee)
Critical and residual states are key soil conditions relevant to slope stability. Evaluating the available shear strength in relation to these conditions is crucial for reliable stability analyses. The best way to determine the strength parameters is through properly selected laboratory tests of soil mechanics. However, in specific cases, these parameters can be estimated based on other material properties of soils. The work clarifies the applicability of various correlation equations from the literature and proposes new relationships, created from laboratory- determined results of strength and index parameters of soils from the Bohemian Central Mountains. It shows how different equations or different material properties of soils can predict the required value of strength. The work also describes how the residual strength of soils and its estimation can be affected. This is mainly caused by the clay fraction proportion and by the shear rate used in its laboratory determination. The results are applied to a specific geotechnical problem - to estimate the critical state and the residual friction angle of soils from the selected study area of the D8 motorway, which is well known thanks to the stability problems. Last but not least, various errors and misunderstandings are discussed, which are often...
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