Ústav geotechniky

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Settlement Analysis of the Nivy Tower in Bratislava by the Finite Element Method
(Faculty of Civil Engineering of The Slovak University of Technology, 2024-10-04) Chalmovský, Juraj; Červenka, Jan; Dobrovolský, Ján; Račanský, Václav
A settlement analysis of a new high-rise building, the Nivy Tower, in Bratislava, Slovakia, is presented in this paper. A 3D finite element model was prepared. A non-linear elasto-plastic material model with double hardening and increased stiffness in a small-to-very-small strain range was adopted for the Tertiary (Neogene) subsoils. Due to the lack of an appropriate in-situ test, the results from a 1D compression test were used for the calibration of the soil input parameters. However, the results from these tests, especially in the primary loading, are often biased due to the effects of soil disturbance during the preparation of the sample. Therefore, a different procedure has been proposed, in which the stiffness parameters were obtained from unloading-reloading branches of 1D compression tests. It could be concluded that the predicted and measured settlements are in a reasonable match for all the points measured. The computed distributions of the vertical displacements and those measured by sliding micrometres show greater differences from a depth of twenty meters beneath the foundation slab.
Optimization of Load-transfer Functions for a Large-diameter Pile in Multi-layered Geological Conditions via a Stochastic Search Algorithm
(Budapest University of Technology and Economics, 2024-10-09) Chalmovský, Juraj
The paper presents the combination of the load transfer method (computational model) and the genetic algorithm (optimization model) for the automated inverse analysis of instrumented pile load tests. The output of this process are the input parameters governing the shape of the load-transfer functions and thus the prediction accuracy when the load-transfer method is used as a design tool for deep foundations. The optimization problem is converted into an unconstrained task by applying the static penalty approach. Two types of measurements are considered in a newly proposed objective function: the load-displacement curve monitored in a pile head and the axial force profiles along a pile derived from strain gauges. Firstly, the local sensitivity analysis via the Design of Experiments is carried out to identify the parameters of the genetic algorithm which significantly influences the rate of convergence during the optimization process. Subsequently, a fully automated inverse analysis of the loading test of the large-diameter bored pile in multilayered geological conditions is presented. The simultaneous combination of two instrumentation sources leads to a stable unique solution with a sufficient match between the prediction and measurements despite a larger number of unknown - optimized variables.
The load-transfer method as a tool for determining the load-displacement curve of piles
(CZECH TECHNICAL UNIV PRAGUE, 2024-09-08) Chalmovský, Juraj; Račanský, Václav; Koudela, Pavel; Zdražil, Karel
The paper presents two applications (software packages) in which the load-transfer method is used for axially loaded Kelly drilled bored piles and displacement ductile iron piles. In the first, the ultimate friction is related to the effective stress via the so-called beta method. The beta method is refined into three stages to cover the variety of soils typical of Central Europe. For the driven piles, a different approach is presented in which the ultimate shaft friction is related to the reference hammering time. The recorded hammering time profile is fed directly into the software based on the load-transfer method. Analyses of five loading tests are presented proving that the load transfer method in combination with the beta method or the recorded hammering time profile is able to compute the load-displacement curve of both replacement and displacement piles with a reasonable accuracy in various geological conditions.
Heat storage efficiency and effective thermal output: Indicators of thermal response and output of radiant heating and cooling systems
(Elsevier, 2020-12-15) Krajčík, Michal; Šikula, Ondřej
An alternative indicator of thermal response of radiant heating and cooling systems called heat storage efficiency (HSE) has been tested. The heat storage efficiency was compared with established indicators represented by the time constant tau(63), response time tau(95), and thermal energy stored (TES). The comparison was performed for three wall cooling systems with various combinations of pipe location, configuration of material layers, and materials of the thermal core. Considering the whole response curve (HSE) instead of focusing on one specific point on the curve (tau(63), tau(95)) allowed comparing the thermal response of complex systems by a single value. It also permitted predicting thermal response consistently regardless of the system and core material. Thermal energy stored predicted the thermal response of certain systems, but it may not be suitable for comparing the thermal response of radiant systems with different thermal admittance. Besides, a novel indicator of thermal output called effective thermal output (ETO) has been proposed. The effective thermal output considers both the steady-state thermal performance represented by the nominal thermal output and dynamic thermal performance represented by the heat storage efficiency. For thermally active building systems (TABS), effective thermal output was up to 57% lower than the nominal thermal output. (C) 2020 Elsevier B.V. All rights reserved.
Lead isotope evolution of the Central European upper mantle: Constraints from the Bohemian Massif
(CHINA UNIV GEOSCIENCES, BEIJING, 2020-05-15) Krmíčková, Simona; Krmíček, Lukáš; Romer, Rolf L.; Ulrych, Jaromír
The Pb isotope composition of the upper mantle beneath Central Europe is heterogeneous due to the subduction of regionally contrasting material during the Variscan and Alpine orogenies. Late Variscan to Cenozoic mantle-derived melts allow mapping this heterogeneity on a regional scale for the last ca. 340 Myr. Late Cretaceous and Cenozoic anorogenic magmatic rocks of the Bohemian Massif (lamprophyres, volcanic rocks of basanite/tephrite and trachyte/phonolite series) concentrate mostly in the Eger Rift. Cretaceous ultramafic lamprophyres yielded the most radiogenic Pb isotope signatures reflecting a maximum contribution from metasomatised lithospheric mantle, whereas Tertiary alkaline lamprophyres originated from mantle with less radiogenic Pb-206/Pb-204 ratios suggesting a more substantial modification of lithospheric source by interaction with asthenospheric-derived melts. Cenozoic volcanic rocks of the basanite/tephrite and trachyte/phonolite series define a linear mixing trend between these components, indicating dilution of the initial lithospheric mantle signature by up-welling asthenosphere during rifting. The Pb isotope composition of Late Cretaceous and Cenozoic magmatic rocks of the Bohemian Massif follows the same Pb growth curve as Variscan orogenic lamprophyres and lamproites that formed during the collision between Laurussia, Gondwana, and associated terranes. This implies that the crustal Pb signature in the post-Variscan mantle is repeatedly sampled by younger anorogenic melts. Most Cenozoic mantle-derived rocks of Central Europe show similar Pb isotope ranges as the Bohemian Massif.

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