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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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Numerical analysis of the colapse of an Nicoll Highway excavation in Singapore
Fabianová, Klára ; Mašín, David (advisor) ; Hrubešová, Eva (referee)
The diploma thesis dealt with collapse of deep excavation which occurred 20th April 2004 in the souhteast part of Singapore. The collapse of temporary retaining system was caused mainly by incorrect setting of Mohr-Coulomb material model in software called Plaxis. The collapse is analyzed by hypoplastic model for clays in this thesis. Hypoplastic model can simulate better behaviour of two main layers of local profile which are marine clay. The simulation of collapse of deep excavation, done by hypoplastic model, was realized in Plaxis software. The results were compared with measurement of inclinometers and also with simulation in witch Mohr-Coulomb model was used. Predictions of hypoplastic model mostly overestimate deformation of diaphragm walls of the excavation and results of Mohr-Coulomb model are very similar. It seems that final predictions of hypoplastic model are influenced mostly by strength than by nonlinearity of stiffness.
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Sources and evaluation of variability of mechanical properties of coarse-grained soils
Mayer, Petr ; Mašín, David (advisor) ; Suchomel, Radek (referee)
This thesis builds on the work of Dr. Radek Suchomel (2011), which dealt with the use of probabilstic methods in geomechanics and discusses the issues associated with inaccuracies in laboratory experiments. For this purpose it was necessary to design and prepare a set of laboratory experiments so as to obtain sufficient data for evaluation, calibrated, hypoplastic constitutive model, which is defined parameters φc, hs, n, ec0, ei0, ed0, α and β. On the basis of these parameters, the data was compared. For this purpose it was appropriate to 40 measuring the angle of repose, 40 triaxial tests and 40 oedometric tests on coarse-grained soil that was sand with missed fraction < 0.063 mm fraction and without fraction > 3 mm, which was classified as the same grain soil, poorly sorted. On this soil is managed successfully to evaluate fully the parameters for 38 samples. Two samples failed to calibrate only the parameters α and β. Test results and subsequent calibration of parameters hypoplastic constitutive model intended that observed variability affects the resulting values of eight parameters hypoplastic constitutive model, which is largely discussed, where there is a comparison with data of Suchomel (2011). With the help of coefficients of variation and standard deviations are concluded that some of...
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Thickness of overburden and overconsolidation of Brno Clay
Pavlová, Martina ; Boháč, Jan (advisor) ; Mašín, David (referee)
Knowledge of the thickness of the overburden of sediments is important in tackling different geological and geotechnical issues. This Bachelor Thesis deals with the available methods for determining the original overburden thickness and with the possible errors from the point of view of the soil mechanics. The area of interest is the northern part of the Vienna Basin, in the vicinity of the town of Brno. The sediments in question are Miocene clays, known locally as Brno Tegel. Consequently the Thesis includes also a brief description of the geological origin of the Carpathian Foredeep.
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Variability of mechanical properties of coarse-grained soils
Zmek, Petr ; Mašín, David (advisor) ; Boháč, Jan (referee)
In a domain of geotechnical engineering, numerical models are used in different situations with success. As an example, numerical models are used in slope stability analyses in different geological environments. To calibrate numerical model for specific geological conditions many samples have to be taken and analysed. One of the parameters of constitutive models is an angle of repose. The angle of repose was measured by four different methods. Subsequent statistical analyses proved a difference between the chosen methods.
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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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Numerical model of NATM tunnel in stiff clays
Svoboda, Tomáš ; Mašín, David (advisor) ; Hilar, Matouš (referee) ; Barták, Jiří (referee)
Disertační práce představuje aplikaci hypoplastického konstitučního modelu při realizaci NRTM tunelu v prostředí městské zástavby s cílem obdržet "class A" predikce chování zeminového masivu. Tunely Královo Pole tvoří hlavní konstrukci severní části Velkého městského okruhu v Brně. Tunely o šířce 14 m a výšce 12 m jsou raženy v prostředí tuhých brněnských jílů s výškou nadloží v rozmezí 6 až 21 metrů. Materiálové parametry hypoplastického modelu kalibrované na výsledky laboratorních experimentů byly optimalizovány využitím dat geotechnického monitoringu a následně použity při simulacích tunelu. Po průchodu ražby profilu tunelu zvoleným úsekem staničení došlo k vyhodnocení prediktivních schopností a vhodnosti konstitučního modelu. Druhým konstitučním modelem použitým při simulacích průzkumné štoly a plain strain analýze tunelu je Mohr - Coulombův model. Metoda redukce napětí využitá v procesu optimalizace parametrů byla vyhodnocena formou porovnání s 3D simulacemi. K vyhodnocení posloužily simulace třech skutečných podzemních konstrukcí s nízkým nadložím realizovaných v prostředí tuhých jílů. Abstract The thesis demonstrates the application of a hypoplastic model in class A predictions of a NATM tunnel in an urban environment. The Kralovo Pole tunnel is a main construction of a northern part of a...
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Horizontal stress in Brno Clay determined by oedometer test
Krupička, Martin ; Boháč, Jan (advisor) ; Mašín, David (referee)
This Thesis deals with the determination of horizontal effective stress in-situ the clay massif in the city of Brno. To determine the value of the horizontal in-situ stress was at first established value of the coefficient of earth pressure at rest K0, which captures stress conditions in the massif and which is a main part of this Thesis. To determine the value of K0 was used the method of the ratio of the horizontal to vertical preconsolidation pressure. Pseudo-preconsolidation pressure used to calculate K0 was determined by using standard oedometer compression tests of oriented undisturbed samples. Research part of the Thesis deals with the issues of evolution of K0 during secondary compression and results of previous published data. The results obtained from own experiments are discussed and compared with the results of previous published data.
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