Search

The ageing of dams is one of the major challenges in specifically Slovenian and generally global dam engineering. Dams are exposed to environmental (climate) changes, as well as time-dependent effects, such as changes in the operating schedules of dams intended primarily for hydroelectric production. These changes can accelerate dams’ ageing and lead to a decrease in their structural and operational safety. Dams are an important part of the infrastructure, as they bring about numerous benefits and at the same time they are also sources of risk. For example, in the event of partial or total failure they pose significant risk to downstream areas. Aging of dams, preserving their functionality, and maintaining their structural health are currently the main challenges of dam engineering. The mean age of Slovenian dams is already over 40 years, although Slovenia is not unique in this situation. In this paper there is presented a novel methodology to monitor structural health of concrete dams, with the use of noncontact and contact measurements through observation of structural vibrations. We present the in-situ experiment on the Brežice dam that began during the dam’s construction and continued into the first year of its operation.

Heat transfer within the soil is a complex process in the presence of seepage flow. In such conditions, the soil’s thermal behavior is influenced by the thermal and hydraulic properties of the medium as well as the initial conditions and boundary conditions to which the medium is subjected. This paper presents the experimental and numerical studies of heat transfer within the sand subjected to the seepage flow. It focuses on the influence of saturated hydraulic conductivity and the porosity of medium on the heat transfer process. The temperature distribution within the sand was monitored by the optical fiber Distributed Temperature Sensor (DTS). The experiment was performed on three types of silica-dominated sands with different saturated hydraulic conductivities and different Soil Water Characteristic Curve (SWCC). In addition to the experimental study, a coupled hydrothermal numerical model was designed in FEFLOW software and validated by comparing its results with the experimental measurements. To determine the influence of porosity and saturated hydraulic conductivity on heat transfer, we analyzed the numerical models for different values of porosity and saturated hydraulic conductivity. The numerical and experimental studies showed that the thermal velocity is higher in sand with higher saturated hydraulic conductivity and temperature declination occurs more quickly due to the heat convection process. Saturated sand with larger porosity has an overall higher heat capacity, wherefore the temperature declination started later in the measuring points but dropped down lower close to the temperature of the upstream water. Přenos tepla v půdě je složitý proces za přítomnosti prosakujícího toku. Za takových podmínek je tepelné chování půdy ovlivněno tepelnými a hydraulickými vlastnostmi média, jakož i počátečními podmínkami a okrajovými podmínkami, kterým je médium vystaveno. Tento článek představuje experimentální a numerické studie přenosu tepla v písku vystavenému průsakovému toku. Zaměřuje se na vliv nasycené hydraulické vodivosti a pórovitosti média na proces přenosu tepla. Distribuce teploty v písku byla monitorována snímačem distribuované teploty z optického vlákna (DTS). Experiment byl proveden na třech typech písků s převahou oxidu křemičitého s různými nasycenými hydraulickými vodivostmi a odlišnou charakteristickou křivkou půdy (SWCC). Kromě experimentální studie byl v softwaru FEFLOW navržen spojený hydrotermální numerický model a ověřen porovnáním jeho výsledků s experimentálními měřeními. Abychom určili vliv pórovitosti a nasycené hydraulické vodivosti na přenos tepla, analyzovali jsme numerické modely pro různé hodnoty pórovitosti a nasycené hydraulické vodivosti. Numerické a experimentální studie ukázaly, že tepelná rychlost je vyšší v písku s vyšší nasycenou hydraulickou vodivostí a pokles teploty nastává rychleji v důsledku procesu tepelné konvekce. Nasycený písek s větší pórovitostí má celkově vyšší tepelnou kapacitu, proto pokles teploty začal v měřicích bodech později, ale klesl dolů níže blízko teploty vody proti proudu.

Based on published research on modifying the structure of water and water-containing systems, we assess external influence methods: temperature, magnetic field, light radiation, and their combination. We evaluate changes in the electrophysical, photo- and pH-metric biological, therapeutic, and other properties of water systems using non-destructive electrophysical research methods, i.e., thermometry, pH, laser interference, dynamic light scattering, microelectrophoresis, conductivity, surface tension, dielectric constant, polarimetric measurements, atomic force microscopy, and UV and EPR spectroscopy. The effects of temperature or magnetic field lead to a change in the content and size of water clusters, and physicochemical, biological, therapeutic, and other changes in the properties of water and water-containing systems. The combined effect of a magnetic field and curative mud and the impact of magnetised mineral water have a more pronounced therapeutic effect than only mineral water or curative mud. The data presented indirectly indicate structural changes in water and water-containing systems. We conclude that the primary mechanism of action of a magnetic field, light, or a combination of these factors on water and water-containing systems, including mineral water and therapeutic mud, is a change in the structure of water.

The paper presents the design and static analysis of a high arch dam. A feasibility study was conducted on the dam in the 90s and a preliminary layout was designed. However, the dam’s construction phase has been never started. In this paper, the design and layout of the dam under consideration are in accordance with the US manuals for the design of arch dams. The structure’s three-dimensional model was entered into the program SAP2000 and three-dimensional solid finite elements were used to discretize the model. This paper considers the hydrostatic pressure of the water reservoir and concrete self-weight. The analysis was performed for both the maximum and the minimum designed water level and for the case when the reservoir is empty. Special attention is given to the boundary conditions of the dam at its abutments and foundation. The results show that the planned layout is good for the dam’s construction. The arch dam’s curve transfers the loads to the abutments. The significant role of the foundation rigidity and the reservoir water level in the stress distribution and nodal displacements within the arch dam is observed.

The development of the hydrology of The Danube River Basin has a long tradition from nineteen century and beyond. Cooperation in hydrology science started 1961 and up to day, 28 scientific conferences have been performed. Since 1975, cooperation between hydrologists of the Danube River Basin has been conducted within the framework of the International Hydrological Programme (IHP) of UNESCO and IHP National Committees established common Cooperation of the Danube River Countries. In addition, Cooperation produce several reports and two books. Cooperation IHP Danube propose common statements for further research and appeal for development water station network necessary for measurement of anthropogenic and climate change impacts.

Seepage is the key factor in the safety of dikes and earthfill dams. It is crucial to identify and localize the seepage excesses at the early stages before it initiates the internal erosion process in the structure. A proper seepage monitoring system should ensure a continuous and wide area seepage measurement. Here, continuous monitoring of seepage at the laboratoryscale is achieved by a passive optical fiber Distributed Temperature Sensing (DTS) system. An experimental model was designed which consists of initially unsaturated sand model, water supply, seepage outflow, optical fiber DTS system, and water and air temperature measurement. Initially, the sand temperature was higher than the temperature of the seepage water. An optical fiber DTS system was employed with a hightemperature resolution, short sampling intervals and short time intervals for temperature monitoring in the sand model. In the system, the small variation in the temperature due to groundwater flow was detected. The numerical analysis was conducted for both the seepage process and the heat transfer progression in the sand model. The results of the heat flow simulation were evaluated and compared with the measured temperature by the optical fiber DTS. Obvious temperature reduction was obtained due to seepage propagation in the sand. The rate of temperature reduction was observed to be dependent on the seepage flow velocity. Proudění je klíčovým faktorem bezpečnosti hráze a přehradních nádrží. Je velmi důležité identifikovat a lokalizovat excesy prosakování v raných stádiích před tím, než zahájí proces vnitřní eroze. Řádný systém monitorování prosakování by měl zajistit nepřetržité měření prosakování - v laboratorním měřítku pomocí pasivního optického vlákna distribuovaného snímání teploty (DTS). Experimentální model byl sestaven z původně nenasyceného pískového modelu, přívodu vody, odtoku, systém optických vláken DTS a měření teploty vody a vzduchu. Zpočátku byla teplota písku vyšší, než teplota protékající vody. Systém optických vláken DTS byl použit s vysokým teplotním rozlišením, krátkými intervaly odběru vzorků a krátkým časem intervalů pro sledování teploty v pískovém modelu. Numerická analýza byla provedena pro jak prosakovací proces, tak i postup přenosu tepla v pískovém modelu. Výsledky simulace tepelného toku byly vyhodnoceny a porovnány s naměřenou teplotou pomocí optického vlákna DTS. Zřejmé snížení teploty bylo dosaženo díky prosakování v písku. Bylo pozorováno, že rychlost snižování teploty je závislá na rychlosti prosakovacího proudu.

This paper presents the first application of the Laser Doppler Vibrometer (LDV) in non-stationary conditions within a hydropower plant powerhouse. The aim of this research is to develop a methodology to include non-contact vibration monitoring as part of structural health monitoring of concrete dams. We have performed in-situ structural vibration measurements on the run-of-the-river Brežice dam in Slovenia during the start-up tests and regular operation. In recent decades, the rapid development of laser measurement technology has provided powerful methods for a variety of measuring tasks. Despite these recent developments, the use of lasers for measuring has been limited to sites provided with stationary conditions. This paper explains the elimination of pseudo-vibration and measurement noise inherent in the non-stationary conditions of the site. Upon removal of the noise, fatigue of the different structural elements of the powerhouse could be identified if significant changes over time are observed in the eigenfrequencies. The use of laser technology is to complement the regular monitoring activities on large dams, since observation and analysis of integrity parameters provide indispensable information for decision making and maintaining good structural health of ageing dams.

This study presents a procedure for modeling the heat transfer process in a concrete dam, taking into account the time-varying boundary conditions on the upstream and downstream sides of the dam (i.e., the water level of the reservoir, spillover, insolation, and shading) which affect the temperature conditions of the dam. The large concrete arch-gravity Moste Dam (in North West Slovenia) was analyzed, where an automated system for the measurement of concrete and water temperatures, and for the monitoring of meteorological effects, was installed. Thermal analyses (1D and 2D) for non-linear and non-stationary heat conduction through solids were performed using a finite element method (FEM) based program, TeEx, which was complemented by two specially developed programs for determining the effects of convection and insolation, considering also the effect of shading. A 15-day period was analyzed, as well as a period of one year. It was found that the results of the performed analyses fitted in well with the experimentally determined concrete temperature measurements. The results showed that at the insolated side of the dam, the temperature gradient was largest in a very narrow area along the concrete surface, but the temperature did not stabilize shallower than at a depth of about 6 m. As part of the thermal analyses, uncertainty analyses of the results of the calculations were also performed.

The paper presents and analyzes the results of the underwater abrasion tests of Cementitious Acrylic Coating (CAC), which was used to protect the repaired surface of concrete dam and stilling basin of power-plant Moste on river Sava in Slovenia. Behavior of the CAC obtained with laboratory tests is rather similar to the behavior obtained after 1 year of application on the power-plant. Relatively good underwater abrasion resistance of CAC was obtained. Results of bond strength show that pressure of capillary water decreases bond between CAC and concrete surface. If such coating is additional loaded with abrasion forces, bond between those two layers becomes worse. Similar conclusions can be made on the basis of the obtained results of surface resistance to freeze-thaw test of CAC has been carried out. The resistance is rather good, but CAC separated from concrete surface, when water is present in the interface between the CAC and concrete surface during freeze-thaw loading.

This paper presents development of three-dimensional characterization of concrete abrasion using the ASTM C1138 test method, which simulates underwater abrasion. To this effect, a measuring system was designed based on laser triangulation with linear illumination of the surface measured. The system allows for contactless, quick and precise measuring of average wear and other topological characteristics dependent on the type of the tested concrete. Validation results show that the system’s precision is better as conventional weighting method (

This paper presents an efficient mathematical model for studying the slip-buckling behaviour of longitudinally delaminated elastic Reissner’s two-layer composite columns. The present mathematical model is used to evaluate exact critical buckling loads of these columns for the first time. The results prove that the presence of longitudinal delamination can significantly reduce the critical buckling load. The comparison of the results show that if sections outside of full delamination are undelaminated, the results are identical to the ones in the literature. On the other hand, the significant discrepancy may exist when those sections are partially longitudinally delaminated. Moreover, the critical buckling load for shear-stiff column with almost freely sliding longitudinal delamination along the whole column length can be up to approximately 4 times smaller compared to the buckling load of the same but undelaminated column.

The paper presents a review of structural measures that were taken to cope with floods in some cities along the Danube River, such as Vienna, Bratislava, and Belgrade. These cities were also considered as case studies within the KULTURisk project. The structural measures are reviewed and compared to each other according to the type, duration of application, the return period of the design flood event, how the project measures are integrated into spatial planning and the problems that occur in the flood defences today. Based on this review, some suggestions are given on how to improve the flood risk management in flood-prone areas.

This paper deals with the heat transfer analysis of the 63-year-old and 60-m-high Moste concrete arch-gravity dam, located in Northwest Slovenia. The analysis was performed after a new sophisticated monitoring system had been established, making it possible to perform continuous measurements of the temperatures of the concrete, water, and dam surroundings, i.e., air temperatures and amount of solar insolation. An equation defining nonlinear and nonstationary heat conduction in the case of a two-dimensional space, for a homogeneous isotropic solid whose thermal conductivity is independent of temperature, was solved numerically by means of the finite-element method, taking into account appropriate boundary conditions. The latter involved the effects of changing conditions in the surroundings (i.e., shading, convection, and solar radiation) during the analyzed period of 15 consecutive clear days in the summer. The results show that the measured and calculated temperatures of the concrete at different...

A mathematical model for slip-buckling has been proposed and its analytical solution has been found for the analysis of layered and geometrically perfect composite columns with inter-layer slip between the layers. The analytical study has been carried out to evaluate exact critical forces and to compare them to those in the literature. Particular emphasis has been placed on the influence of interface compliance on decreasing the bifurcation loads. For this purpose, a preliminary parametric study has been performed by which the influence of various material and geometric parameters on buckling forces have been investigated. (C) 2009 Elsevier Ltd. All rights reserved.

Check dams as a typical torrent structure behave as retention structures typically storing torrent sediments in order to stabilise the torrential bed. If such structures are damaged and partially broke down, stored torrent sediments may cause sediment–related disasters in the downstream torrent’s reaches or on torrential fans. A field study on the status of 22 check dams in the Upper Sava River in NW Slovenia with regard to their structural stability was performed to answer a question whether they should be taken as a possible debris-flow source. For this purpose we used the existing inventory (cadastre) of water infrastructure in torrents and field survey. The resulted hazard assessment showed rather high debris-flow risk for downstream infrastructure in the lower parts of the investigated torrential watersheds. That is why we should treat some check dams as “large” dams.

Large sediment-retention dams, built in a cascade (a chain of check dams), can impose hazard (hyper-concentrated sediment flow, debris flow), if they fail during torrential flash floods or when destroyed by overtopping by a debris flow initiated on slopes or in natural torrential channels. Using estimates of specific annual sediment yields in torrential watersheds on one hand, one can use the area of the watershed and the storage volume of torrential check dams in order to estimate the maximum potential of sediment stored in the retention volume of the check dams—as a first approximation for the magnitude of the debris flows initiated by the dam failure. On the other hand, one can use debris-flow susceptibility maps to estimate likelihood for triggering of potential debris flows in torrential watersheds under investigation (we used debris-flow susceptibility map of Slovenia in the scale 1:250,000). A field study on the status of several tens of check dams in the Upper Sava River in NW Slovenia with regard to the question whether they should be taken as a possible debris-flow source was performed.

The paper deals with the issues of resistance of concrete linings to long-term abrasion loading caused by waterborne particles, particularly for the proposed hydro power plants on the Sava River in Slovenia. The main purpose of the research work was to define the possibility of forecasting the process of concrete lining wear on the Sava River dam structures based on the standard procedures of abrasion resistance testing. Abrasion resistance of concrete has been researched in accordance with the standard ASTM C 1138 and Bohme (DIN 52108) methods. The research work was based on a comparison between laboratory results and measurements of abrasion resistance of concrete under natural conditions by performing test plots in the stilling basin of the Vrhovo HPP. Concrete composites with different mechanical properties have been analysed within the research programme. The analysis showed a qualitative similarity of the level of concrete abrasion between laboratory simulations and measurements in the field, as well as suitability of the ASTM C 1138 laboratory method for the assessment of abrasion resistance of concretes in the spillway of the HPP chain on the Lower Sava River.

Construction of a chain of hydro power plants is planned on the Sava River from Medvode to the Slovenian-Croatian border which will, apart from the chain of HPPs on the Drava River, represent the linchpin of renewable energy production within the Slovenian power system. The mentioned chain of HPPs will also be one of the country's main renewable energy sources that can still be developed for power generation. Three hydro power plants, Moste, Mavccice and Medvode, are already operating on the Upper Sava River section. Construction of the chain is underway in the lower part of the stream where Vrhovo and Bosstanj HPPs are already in operation; HPP Blanca is under construction and the site planning procedures are taking place for Krsko, Brežice and Mokrice HPPs. The planned HPPs on the Middle Sava River section between Medvode and Zidani most will connect the HPPs on the Upper and Lower Sava River into a closed chain which will operate on the principle of run-of-river type power plants with daily storage. Completion of all stages will enable optimal development of available hydro potential. Apart from the energy effects, also other beneficial effects of hydro power plant construction in the region can be expected: flood protection; better water supply; waste water treatment; development of transport and energy networks as well as positive economic and social effects.

The exact analytical solution of buckling in delaminated columns is presented. In order to investigate analytically the influence of axial and shear strains on buckling loads the geometrically exact beam theory is employed with no simplification of the governing equations. The critical forces are then obtained by the linearized stability theory. In the paper, we limit the studies to linear elastic columns with a single delamination, but with arbitrary longitudinal and vertical asymmetry of delamination and arbitrary boundary conditions. The studies of quantitative and qualitative influence of transverse shear are shown in detail and extensive results for buckling loads with respect to delamination length, thickness and longitudinal position are presented. (c) 2007 Elsevier Ltd. All rights reserved.