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Study on the combined impact about joint dip angle and rock thickness on the excavation stabilities of tunnels with large-span based on numerical experiment
Get PDFThe stabilities about surrounding rocks are closely related to the characteristics of the joints when tunnel passing through layered joint rock masses. However, existing research has mainly focused on the stabilities about tunnels in single joint rock masses, and there is still little attention paid to situations with large spans and complex geological conditions. Therefore, based on the Chongqing Guobo Station Tunnel Project, using numerical experimental method, this paper conducts in-depth research on the relationship between joint dip angle, joint rock layer thickness and surrounding rock stabilities of tunnel. The research findings indicate that changes in joint dip angle and joint layer thickness largely influence the stabilities about surrounding rock, and the maximum increment of tunnel deformation under different conditions is close to 400mm. The deformation about the surrounding rock displays a tendency of first slowing down while then rising with the inclination angles. The difference between the displacement in the directions perpendicular to the joint surface and the directions along the bedding plane first decreases and then increases, ultimately dominated by the displacement in the bedding direction. The maximum displacement gradually moves from the arch shoulder to the crown. For the large joint dip angles, surrounding rock mainly experiences tensile yield failures along joint’s surface direction, and shear yield failure perpendicular to the joint surface direction. When the thicknesses about joint layer increases, the displacement about surrounding rock as well as distribution range in plastic zone decrease, the overall integrity about surrounding rock improves, and the stability is enhanced. The research results of this article can be valuable guidance for analogous project in the future.
Received: 13.12.2024
Received in revised form: 15.7.2025
Accepted: 1.9.202
Analysis of historic (80+) concrete structure exposed to weathering
Get PDFCílem studie byla analýza historické betonové konstrukce z 30. let 20. století a následná analýza poruch vzniklých vlivem působení vody v konstrukci. V rámci studie bylo provedeno dlouhodobé měření vlhkosti vybrané konstrukce a okrajových podmínek (teplota vzduchu a relativní vlhkost vzduchu). Měřením ve více místech konstrukce hloubkovými kartáčovými sondami bylo potvrzeno, že v masivních historických betonových konstrukcích vystavených vnějším podmínkám je poměrně vysoký obsah vody uvnitř konstrukce (nejčastěji kolem 4%). To je způsobeno zejména velkou mezerovitostí a pórovitostí struktury starého betonu. Vlivem působení vody v historických betonových konstrukcích dochází k chemickým reakcím, jejichž produktem jsou výluhy chemikálií pronikající na vnější povrch konstrukce. Provedenou chemickou analýzou výluhu bylo zjištěno, že dominantním prvkem byl podle očekávání vápník (naměřeno 92,42 - 95,32 %). Navzdory umístění konstrukce v zemědělské ploše vystavené hnojení, byl naměřený obsah dusičnanů ve vzorku pouze 0,031%. Mikroskopická analýza potvrdila potenciální možnost rekrystalizace vápníku, která může ohrozit trvanlivost sanačního zásahu a je proto nezbytné toto zohlednit při návrhu sanace. V rámci analýzy byly vytvořeny vzorky historického betonu dle dochované receptury z 30. let 20 století. Tyto vzorky byly podrobeny měření difuzní propustnosti - průměrný součinitel difuze byl naměřen D = 8,4.10-9 (m2/s). Taková difúzní propustnost odpovídá betonu o horší kvalitě i přesto, že vzorky byly nově vytvořeny – tyto vlastnosti tedy měla konstrukce již v době své realizace před 80 lety, pozdější degradace betonu na to měla již pouze minimální vliv.The aim of the study was to analyze historic concrete structures from the 1930s and then to analyze the failures caused by water action on the structures. As part of the study, long-term moisture measurements were taken on a selected structure along with boundary conditions (temperature and relative humidity). By taking measurements at multiple locations on the structure using depth brush probes, it was confirmed that massive historic concrete structures exposed to external boundary conditions contain relatively high amounts of water (typically around 4%). This is mainly due to the large voids and porosity of the old concrete structure. The action of water in historic concrete structures leads to chemical reactions. Their products are chemical leachates which penetrate the surface of the structure. The analysis revealed that calcium is the dominant element, with measured values ranging from 92.42 % to 95.32 %. Although the structure studied is located in an agricultural area subjected to fertilization, the nitrate content was measured at only 0.031 %. Microscopic analysis confirmed potential calcium compounds recrystallization, which could jeopardize the durability of the remediation. This factor should therefore be carefully considered in the remediation design. Samples of historic concrete were produced according to the original 1930s recipe. These samples were subjected to diffusion permeability measurements. The average diffusion coefficient D = 8,4.10-9 (m2/s) was measured. Such diffusion permeability corresponds to poor quality concrete, even for the newly formed samples. Thus, the structure had these properties at the time of construction 80 years ago and subsequent degradation has had little effect.
Received: 8.2.2025
Received in revised form: 24.7.2025
Accepted: 30.8.202
Parameter Analysis of Prestressed Steel Wire Rope Strengthened Concrete Beams
Get PDFThis paper systematically analyzes the parameters of prestressed steel wire rope strengthened concrete beams using finite element software ANSYS, aiming to explore the influence of different reinforcement parameters on the flexural performance of the beams. Seven 2.4m concrete beam models with different reinforcement methods were established, including comparisons of factors such as the number of prestressed tendons, tensile control stress, and composite mortar protection. Through simulated loading tests, the deflection changes, stress distribution, and force characteristics of steel bars and steel strands were examined. The results indicate that prestressed reinforcement significantly improves the stress state of the beams: an increase in prestress can effectively reduce the tensile stress at the beam bottom and decrease the stress in the main reinforcement, but has no significant impact on structural stiffness. An increase in the cross-sectional area of prestressed tendons significantly enhances the beam\u27s stiffness. Composite mortar protection, although increasing self-weight, reduces prestress loss and optimizes the stress distribution of the steel strands. In contrast, the steel plate bonding method fails to fully utilize its effectiveness under low loads and even increases the stress in the steel bars. Additionally, excessively high prestress values may lead to excessive tensile stress at the beam bottom, necessitating reasonable design in practical engineering. This study provides a theoretical basis and parameter optimization directions for the engineering application of prestressed steel wire rope strengthened concrete beams, verifying the effectiveness of this technology in enhancing bridge load-carrying capacity and extending service life.
Received: 28.05.2025
Received in revised form: 28.10.2025
Accepted: 24.11.202
Numerical modeling of electric arc in a low voltage breaking chamber
Get PDFThis work presents the development of a MagnetoHydroDynamic (MHD) model to simulate electric arc behavior in a low-voltage circuit breaker chamber. The modeling process began with a simplified geometry to validate key phenomena such as arc displacement, segmentation, and voltage rise, showing good agreement with literature. To approach realistic conditions, contact rotation was implemented using a layering technique, improving numerical accuracy and avoiding mesh deformation.A current-limiting mechanism and electrical network coupling were also introduced, enabling dynamic current input. These modules were integrated into a 3D geometry representing a real chamber, successfully reproducing arc evolution under realistic conditions. The model captures complex arc physics and helps in future design optimization of low-voltage devices
Sensitivity of Synthetic Test Circuit parameters on thermal interruption tests in CO2 gas mixtures
Get PDFSynthetic testing has been extensively utilized to study the thermal interruption performance of CO2-based gas mixtures under the influence of varying physical factors in an experimental HV circuit breaker. To limit contact and nozzle ablation for collecting a statistically meaningful dataset, the lowest possible peak current amplitudes were chosen for the high-current and the injection current phases. The present work focuses on evaluating the sensitivity of the test-circuit parameters on the interruption performance in CO2/O2 (90% /10%) gas mixture
Temporal fusion strategy for violence detection: utilising convolutional and LSTM neural networks for surveillance videos
Get PDFIn the latest intelligent cities, there is a pursuit for the utmost degree of automation and integration of services. One of the major challenges in the surveillance industry is the need to automate real-time video analysis to identify critical cases. This paper introduces sophisticated models using Convolutional Neural Networks (CNN), specifically MobileNet V3, VGG16, and InceptionV3 networks, as well as networks using LSTM and feedforward networks. These models are designed to accurately categorise videos into two completely separate classes, namely: (“Non-Violence” and “Violence”). The RLVS database is used for this classification task. Various data representations are used by Temporal Fusion approaches. The highest attained outcome was an Accuracy of 91.03 %, and an F1-score of 90.90 %, which is superior to the results obtained in similar research performed on the same database for achieving the goal of recognising actions that are violent in Surveillance Videos
Some remarks on a mathematical model for water flow in porous media with competition between transport and diffusion
Get PDFThe contribution deals with the mathematical modelling of fluid flow in porous media, in particular water flow in soils, with the aim of describing the competition between transport and diffusion. The analysis is based on a mathematical model developed by B. Detmann, C. Gavioli, and P. Krejčí, in which the effects of gravity are included in a novel way. The model consists of a nonlinear partial differential equation describing both the diffusion and the gravitational transport of water. Although analytical solutions can be obtained for some special cases, only numerical solutions are available in more general situations. The solving algorithm is based on a time discretisation and the finite element method and is written in Matlab. The results of the numerical simulations are shown and the behaviour of the model is discussed
Effect of hydrogen embrittlement on mechanical properties of non-stressed prestressing steel
Get PDFThe aim of this paper is to elucidate the effect of hydrogen on the structure of commonly used prestressed concrete steel strand (PC strand) of concrete bridges and other structures in the non-stressed state to determine the general behaviour of the characteristic steel material, which would lead to further investigation of specimens in the prestressed state. For the experimental part of the research, a system was set up for saturating the samples with hydrogen, which diffuses into the steel structure in atomic form. These specimens were then subjected to tensile testing according to EN ISO 15630-3 to reveal the reduced mechanical properties of the prestressed concrete steel strand specimen caused by the diffusion of hydrogen into the material structure. After the tensile tests, the fracture surfaces were analysed on a scanning electron microscope to verify the effect of hydrogen
Monitoring the reactivity of pozzolans by thermogravimetric method
Get PDFThis work focuses on comparing the effect of ten different types of pozzolans on the strength of lime pastes in relation to their pozzolanic activities as determined by the Chapelle test and monitoring the reactivity of these pozzolans using the thermogravimetric method. It was found that the Chapelle test can in some cases overestimate the reactivity of the pozzolan due to differences between the conditions during the test and in reality. The strengths of lime-pozzolan pastes did not correlate well with the pozzolanic activity values of the pozzolans used. On the contrary, the amount of reacted lime in the pastes, determined by the thermogravimetric method, correlated very well with the compressive strengths of the pastes
Modelling of switching arcs at short electrode distances
Get PDFProperties of the arc plasma at electrode distances below 1 mm have been studied by one-dimensional time-dependent (1D-t) fluid-Poisson model. Silver vapour is assumed to be the arc medium, as the electrodes mainly contain Ag. Pronounced voltage falls in the near-electrode regions were found. The model predicts clear thermal non-equilibrium as well as negative anode fall in case of small DC currents. For implementation in power grids simulations, a simplified arc model in form of current – voltage characteristics was derived. Predicted modelling results for electrical characteristics at various conditions have been compared with experimental results obtained for a low-voltage DC hybrid switch. A reasonable agreement between predicted and measured data was found