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| 2. |
- Bernstone, Christian
(författare)
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Automated performance monitoring of concrete dams
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Swedish hydropower industry operates a large number of power plants and dams geographically spread over the country. The level of safety of a specific dam is to a large extent determined during the design and construction phases that in the case of Swedish hydropower plants took place several decades ago. Condition monitoring of concrete dams, or hydropower concrete structures, has until recently been an area of relatively low priority. Nevertheless, these structures represent a significant economical value. From a dam safety perspective, the reasons for condition monitoring are not significant. But as high availability has high priority, condition monitoring should be considered as one of the tools to use for assuring this. The objectives of the research carried out within the scope of this Ph.D. thesis have been to adapt and develop cost-effective methods and methodology for the automated performance monitoring of concrete dams and their foundations, with specific attention paid to prioritised damage types. The objective has also been to build new knowledge regarding sensor technology. By doing this, the thesis contributes to improving current praxis for the condition monitoring of concrete structures. The thesis covers a series of tasks that are central to condition monitoring: - The introductory chapter of this thesis is devoted to the set automated performance monitoring of hydropower concrete structures in context: The operation and maintenance of hydropower infrastructure are outlined. Statistics about the dam population are given, together with an outline of the main types of ageing processes and an international outlook on concrete dam condition monitoring. Included is also a condensed state-of-the-art review of instrumentation. An outline is given of how the information gained can be used as part of the technical management of hydropower concrete structures. - The methods-chapter includes the choice of deterioration mechanisms and the methods for monitoring the progress of damage. Each method is described, together with identified requirements for development. - The results-chapter builds upon five technical papers. The results achieved in developing the chosen technologies to the state that they can be applied to real structures in the field are summarised. Results from tests in both the laboratory and in the field are presented. - The discussion and conclusions chapter discuss the results versus the goals, and concludes the improved knowledge established. The barriers to employment are discussed, and the drawings of conclusions about how the results can be used to assist improved decision support regarding maintenance measures are made. Finally, there is a discussion about future improvements. Based on three country reviews of the status of concrete dams, three prioritised damage mechanisms have been identified to be followed up by condition monitoring: crack growth, uplift pressure, and dam-crest deformation. Research has been directed to technology options that have proven records in other applications. Based on the state-of-the-art review, three methods were chosen for further development: Time-domain reflectometry (TDR), Digital imaging together with Image processing, and GPS. An assessment of costs shows that the most cost-effective method is digital imaging and image processing, while the most expensive method is GPS. In total, four condition-monitoring investigations have been demonstrated. These include (i) uplift pressure and (ii) dam crest investigations of the Storfallsdammen in River Dalälven, and crack growth/deformation investigations of (iii) draft tube wall of a hydropower plant (Porjus) and (iv) a commuter bridge (Alvik). In cooperation with other research projects, it has been shown that reliability-based stability safety analysis is a good tool for assessing existing concrete dams. Overall, the work contained in this research contributes to improving the knowledge base on how owners of hydropower concrete structures can incorporate condition monitoring into their regular maintenance work. As a result of the research project, it is judged that the introduction of new tools for the maintenance work practised within the Swedish hydropower industry may be possible with, once installed, only a minor increase in the workload of the maintenance organisations.
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| 3. |
- Bernstone, Christian, et al.
(författare)
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DC resistivity mapping of internal landfill structures: two pre-excavation surveys.
- 2000
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Ingår i: Environmental Geology. - : Springer Science and Business Media LLC. - 0943-0105 .- 1432-0495. ; 39:3-4, s. 360-371
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Tidskriftsartikel (refereegranskat)abstract
- Geophysical investigations using 2-D DC resistivity were carried out on old parts of two similar landfills, with waste of different ages. The data sets, which included high data density in both vertical and horizontal directions, were interpreted with 2-D smoothness constrained inversion. The landfills were excavated after the surveying. The objective was to test the capability of the resistivity method as a pre-characterization technique. The objectives were only partially fulfilled. First, the moisture content was the parameter that appeared to exert the dominant control over the resistivity distribution of the landfill. The most important potential information that can be recovered is, therefore, an indication of the waste piles hydraulics. Second, it was neither possible to estimate the amount of recoverable soils, nor to correlate the type of waste with the resistivity models. However, discrete anomalies were identified, and if specific materials are searched for, the resistivity models indicate possible places to search.
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| 7. |
- Bernstone, Christian, et al.
(författare)
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Image analysis for monitoring of crack growth in hydropower concrete structures
- 2009
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Ingår i: Measurement. - : Elsevier BV. - 0263-2241 .- 1873-412X. ; 42:6, s. 878-893
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Tidskriftsartikel (refereegranskat)abstract
- A digital image analysis technique for crack monitoring using a standard web-camera has been further developed to acquire continuous data sets on crack development in concrete dams. The method is based on an existing robust and straightforward non-contact method for experimental deformation analysis. It allows for the measurement of suspected serious cracks, identified from inspections, through a sequence of images captured at intervals. The crack opening displacements at the surface of investigated objects are obtained by an algorithm that makes it possible to automatically track the motions of discrete markers painted on the object surface markers and compute their centre of mass in a sequence of images. The data acquisition process is straightforward and is well suited for this type of environment. Results from laboratory experiments and a field-test on a commuter bridge in Sweden are presented. The study implies that the technique can be useful for hydropower concrete structure applications. (C) 2009 Elsevier Ltd. All rights reserved.
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| 8. |
- Bernstone, Christian, et al.
(författare)
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Structural Assessment of a Concrete Dam Based on Uplift Pressure Monitoring
- 2009
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Ingår i: Journal of Geotechnical and Geoenvironmental Engineering. - 1090-0241. ; 135:1, s. 133-142
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Tidskriftsartikel (refereegranskat)abstract
- The context of structural monitoring of concrete dams as part of hydropower assets management is described. A tool that fits well into this context is the control of the uplift pressure of concrete dams. A monitoring technique suitable for this purpose was developed based on an automated water-level measurement technique using time-domain reflectometry and standard air-dielectric coaxial cable sensors. The signal is interpreted automatically by applying a threshold method to determine the apparent water level, which is then used to calculate the uplift pressure. A field test at a concrete dam column displayed consistent results, which were used as input to a reliability-based stability safety analysis. The results show that this technique can be very useful for uplift pressure monitoring. The information determined can serve as input to the maintenance work as well as assist engineering decisions.
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| 9. |
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| 10. |
- Bernstone, Christian, et al.
(författare)
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Verifiering av struktur och fuktmekaniska beräkningsverktyg : Tillämpning på reaktorinneslutningars betongkonstruktioner, Vercors Fas 1
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Électricité de France har utanför Paris byggt en 1/3 skalmodell av en reaktorinneslutning motsvarande en fransk fullskalereaktor modell P4. Anläggningen möjliggör studier av hur åldringsprocesser påverkar förspända reaktorinneslutningar. Syftet är att efter de 7 år som ett övergripande forskningsprojektet vid på anläggningen pågår, uppnå påverkan motsvarande den åldring som en fullskalereaktor har utsatts för efter 6o års drift.Konstruktionen har försetts med ett omfattande instrumenteringsprogram som gör det möjligt att följa konstruktionens beteende i tidigt skede och över tid. Ett av anläggningens forskningsprojekt omfattar en benchmark av olika beräkningsverktygs möjlighet att kunna förutse konstruktionens beteende i tidigt skede och under själva åldrandet, dess täthet till följd av åldrandet och beteende under svåra haveriförhållanden. Denna benchmark har genomförts via en öppen inbjudning till intresserade experter att delta. I projektet, benämnt VeRCoRs , bidrar deltagande organisationer med egna modelleringsarbeten utifrån de tre olika teman. Arbetet med det första temat startade 2015 (tidigt skede), därefter följer den åldrade konstruktionen (2017) och svåra haverisituationer (2021). Denna rapport redovisar det arbete som har gjorts för det första temat (Tema 1) inom ramen för ett Energiforskuppdrag.Modelleringsarbetet har till största delen genomförts av LTH i nära samarbete med KTH och Vattenfall. Simuleringar har gjorts för den unga betongens beteende under den ett år långa byggfasen, med hänsyn tagen till betongens hydratation (temperaturberäkningar/värmeutveckling), uttorkning (självuttorkning och fukttransport) och deformationer (temperatur-, fukt-, kryp-, och spänningsrelaterade deformationer). Resultatet har jämförts mot data från anläggningens instrumentering. Dessutom så har en genomgång gjorts av resultaten från övriga deltagares arbeten i Tema 1.Sammanfattningsvis så visar resultaten på de fördelar som finns med att genom avancerade beräkningar verifiera designparametrar och prognostisering av reaktorinneslutningars funktion, men också på utmaningar. Med hjälp av FEmodellering så kan det tidiga skedet efter färdigställd konstruktion beskrivas både vad gäller temperatur- och deformationer med rimlig tillförlitlighet. Det finns dock potential till förbättringar. Även om betongens temperatur kan predikteras noggrant så kan det skilja kraftigt i uppskattningen av inducerade påkänningar. En viktig orsak till dessa skillnader beror på osäkerheter i bestämning av krypning och krympning i betongen tidiga skede.
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| 11. |
- Dahlin, Torleif, et al.
(författare)
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A 3-D resistivity investigation of a contaminated site at Lernacken, Sweden
- 2002
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Ingår i: Geophysics. - : Society of Exploration Geophysicists. - 0016-8033 .- 1942-2156. ; 67:6, s. 1692-1700
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Tidskriftsartikel (refereegranskat)abstract
- A contaminated site at Lernacken in southern Sweden, formerly used for sludge disposal, was investigated using a 3-D resistivity imaging technique. The data acquisition was carried out using a roll-along technique for 3-D data acquisition that allows using standard multielectrode equipment designed for engineering and environmental applications. The technique allows for the measurement of large true 3-D resistivity data sets, and data were measured using two perpendicular electrode-orientation directions with only one layout of the cables. The data were plotted as two sets of pseudo depth slices using the two electrode orientation directions, which resulted in markedly different plots. The complete data set was inverted to form a resistivity-depth model of the ground using a 3-D least-squares smoothness constrained inversion technique. The results obtained were compared to other geophysical and background data, and a good agreement was found. The results show that the 3-D roll-along technique in combination with 3-D inversion can be highly useful for engineering and environmental applications. However, multichannel measurement equipment is necessary to speed up the data acquisition process for routine application.
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| 14. |
- Lundin, Urban, et al.
(författare)
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Adding discharge capacity and redundancy using existing turbines
- 2021
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Ingår i: International journal on hydropower and dams. - 1352-2523. ; 28:5, s. 78-82
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Tidskriftsartikel (refereegranskat)abstract
- The ability to discharge water plays a vital role in hydropower dam safety. There are several different designs that provide discharge capacity, with the two main types being surface and bottom spillways. Here, an alternative concept is presented, whereby the regular waterway through the turbine is utilized. In the event of grid loss a local load is connected which enables the unit in question to operate isolated from the main grid. This dump-load concept has been tested at pilot scale in Sweden with positive results and therefore proposed to be applied in existing power plants. Additional discharge capacity via a dump-load has a number of benefits compared to conventional spillgates, the most obvious being its significantly lower investment cost, fast installation and provision of redundancy.
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| 15. |
- Malm, Richard, 1980-, et al.
(författare)
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Assessing the structural safety of cracked concrete dams subjectedto harsh environment
- 2019
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Ingår i: Sustainable and Safe Dams Around the World. - Canada. - 9780367334222 ; , s. 383-397
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Konferensbidrag (refereegranskat)abstract
- As the dams are aging and the design requirements continuously increase, complexanalyses may be required that consider aspects previously excluded in the original design.Due to the harsh environment in cold regions with significant seasonal temperature variations,many con- crete dams have cracked. The development of cracks may result in internal failuremodes, where parts of the dam may fail. These internal failure modes are thereby primarily governedby the material failure of reinforcement and concrete. When assessing cracked hydraulicstructures, how- ever, many design guidelines are based on global safety factors for stability failuremodes, i.e. overturning and sliding, while the partial coefficient methods are used for thestructural design related to material failures. By using a developed design methodology basedon finite element analysis, all these failure modes but also combinations of different failuremodes can be consid- ered. In this paper, the design methodology is presented and implementedto assess the structural safety of a cracked concrete spillway section. The result provides supportfor dam owners on how to manage pillars of concrete dams subjected to extensive cracking.
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| 16. |
- Norooz, Reyhaneh, et al.
(författare)
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A geoelectrical pre-study of Älvkarleby test embankment dam : 3D forward modelling and effects of structural constraints on the 3D inversion model of zoned embankment dams
- 2021
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Ingår i: Journal of Applied Geophysics. - : Elsevier BV. - 0926-9851. ; 191
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Tidskriftsartikel (refereegranskat)abstract
- Electrical resistivity tomography has potential as a complementary long-term monitoring method in embankment dams; however, the 3D character of the geometry including the shape of the embankment, its internal zoned construction and the reservoir water make interpretation challenging. To tackle this problem, a qualified inversion model considering the 3D environment is necessary. In this paper, prior information about the resistivity of different parts of a test embankment dam was used as constraints in order to increase the capability of defect detection in a complex 3D context. Five small defects were incorporated into the core of the model. Laboratory measurements were made on samples of the materials intended to be used for the construction of a test embankment dam, and resistivity values provided from the laboratory measurements were used in the forward modelling. A measurement sequence of around 8000 synthetic data points using extended gradient, crossline bipole-bipole and corner arrays between horizontal-horizontal, vertical-vertical, and vertical-horizontal lines were modelled and inverted all at once. The structural constraints were applied to increase the accuracy of inversion, using the L1 and L2 methods. Different mesh qualities with different boundaries for each region and 3D geometric factor calculation were applied for the inversion to evaluate the effects of region control incorporated in the inversion process. The results showed that L1 and L2 norm inversions combined with region control can determine the location of very small defects and finding the defects located near each other, respectively. Removing the region control from the inversion caused unrealistic resistivity prediction for some regions and the inability to discover the dam defects. Therefore, the proposed methodology can decrease non-uniqueness in the inversion and make time-lapse ERT a valuable monitoring tool that complements other instrumentation techniques and based on these results it was concluded promising to continue with the construction of the test dam using the same type of defects and electrode set-up, for verification under field-conditions.
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| 17. |
- Norooz, Reyhaneh, et al.
(författare)
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Monitoring internal erosion in embankment dams using 3D Electrical Resistivity Tomography: Älvkarleby test embankment dam
- 2023
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Ingår i: Procs. Near Surface Geoscience 2023.
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Konferensbidrag (refereegranskat)abstract
- One major risk threatening embankment dam integrity is internal erosion of the core. Internal erosion progresses inside the dam but it is difficult to detect with conventional methods. Electrical Resistivity Tomography (ERT) is a potential-based method that can sense the interior of the dam, and this study aims to evaluate the capability of ERT as a complementary monitoring technique for discovering internal erosion. A test embankment dam with some defects incorporated inside the core and fine filter in Älvkareby, Sweden, has been constructed with the purpose of assessing different monitoring techniques including ERT. Buried electrodes and sensors for other monitoring instruments were placed inside the dam. The collected ERT data were inverted using a 3D time-lapse inversion model implemented in pyGIMLI/pyBERT package. The results revealed a layered resistivity structure in the core and several unintentional anomalous zones. Furthermore 2 out of 5 defects in the core were located, namely horizontal and vertical crushed rock zones, with a slight location shift for the horizontal zone. A concrete block defect was indicated, although not as distinctly and with a lateral shift. The two remaining defects, a crushed rock zone at the abutment and a wooden block were not discovered.
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| 18. |
- Norooz, Reyhaneh, et al.
(författare)
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Monitoring of Älvkarleby test embankment dam using 3D electrical resistivity tomography for detection of internal defects
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Ingår i: Journal of Civil Structural Health Monitoring. - 2190-5452.
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Tidskriftsartikel (refereegranskat)abstract
- Electrical resistivity tomography (ERT) is a potential-based method for detecting internal erosion in the core of embankment dams using the electrodes installed outside. This study aims at evaluating the practical capability of ERT monitoring for detecting internal defects in embankment dams. A test embankment dam with in-built well-defined defects was built in Älvkarleby, Sweden, to assess different monitoring systems including ERT and the defect locations were unknown to the monitoring teams. Between 7500 and 14,000 ERT data points were acquired daily, which were used to create the distribution of electrical resistivity models of the dam using 3D time-lapse inversion. The inversion models revealed a layered resistivity structure in the core that might be related to variations in water content or unintentional variations in material properties. Several anomalous zones that were not associated with the defects were detected, which might be caused by unintentional variations in material properties, temperature, water content, or other installations. The results located two out of five defects in the core, horizontal and vertical crushed rock zones, with a slight location shift for the horizontal zone. The concrete block defect in the core was indicated, although not as distinctly and with a lateral shift. The two remaining defects in the core, a crushed rock zone at the abutment and a wooden block and a crushed rock zone in the filter, were not discovered. The results cannot be used to fully evaluate the capability of ERT in detecting internal erosion under typical Swedish conditions due to limited seepage associated with the defects. Furthermore, scale effects need to be considered for larger dams.
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| 19. |
- Norooz, Reyhaneh, et al.
(författare)
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Pre-study for geoelectrical monitoring for detection of internal defects and anomalous seepage in the Älvkarleby test embankment dam
- 2020
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Ingår i: ; , s. 11-11
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Konferensbidrag (refereegranskat)abstract
- Electrical resistivity tomography (ERT) can be used to monitor the interior of hydropower embankments dams, and thereby detect zones with anomalous material properties and flow induced variation in the resistivity caused by changes in total dissolved solids (TDS) and temperature. Furthermore, monitoring of embankment dams in connection with a substantial change in the reservoir water level can detect anomalous leakage paths via differential wetting of zones with different hydraulic properties. In Sweden, where the available hydropower energy capacity is utilised, installation of electrodes must be done post-construction of embankment dams, which for practical reasons generally means installed along its crest, in the top of the core, using a 2D ERT approach. This has the advantage of focusing the sensitivity to the core itself, which is the part of the dam that shall stay impervious over time. However, the orientation of the electrode layout in combination with the 2D approximation leads to severe 3D effects, which distorts the inverted model resistivities and geometry. Furthermore, the resolution decreases with depth, which is a major limitation for high dams. A way ahead would be if electrodes could be installed on deeper levels inside the dam close to the core, which might be possible using modern drilling technology. This electrode lay-out concept was investigated with numerical modelling using extended gradient, cross-line bipole-bipole and corner arrays between horizontal-horizontal, vertical-vertical and vertical-horizontal lines respectively. To interpret the data 3D inversion is required to handle the structure’s geometry due to the zoned construction with materials that have large contrasts in resistivity. A test embankment dam installation was built during the autumn of 2019, with electrodes and various sensors installed inside the dam to evaluate the applicability of the suggested approach. We present results of numerical modelling simulating potential defect scenarios where several measurement sequences of close to 8,000 data points using the abovementioned arrays are inverted all at once. In order to resolve subtle variations inside the core, the finite element grid design is based on prior knowledge about the internal material distribution, with broken smoothness constrains at known material boundaries. In combination with region-based control of the resistivities of the different material zones, the inversion in combination with a time-lapse approach it shows promising results.
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| 20. |
- Salas Romero, Silvia, et al.
(författare)
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Blind testing using seismic methods for detecting flaws in an experimental embankment dam in Älvkarleby, Sweden
- 2020
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Ingår i: Conference Proceedings, NSG2020 26th European Meeting of Environmental and Engineering Geophysics, Dec 2020, Volume 2020, p.1 - 5. - : European Association of Geoscientists & Engineers.
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Konferensbidrag (refereegranskat)abstract
- One of the most common failures in embankment dams is internal erosion of the body and in the foundation. Vattenfall leads a joint research project for assessing the potential of geophysical methods for detecting flaws (with unknown position and size) within the core of an experimental dam in Älvkarleby, Sweden. Equipment for measuring seismic, resistivity and temperature data were installed within the core at different depths and in other areas of the dam. In this study, seismic investigations, such as P-wave reflection seismic and P-wave traveltime tomography, focused on testing and, if possible, detecting the built-in flaws in an early stage before water filling the dam. The reflection seismic results for the top middle and upstream hydrophone lines show high resolution in the first meters of the sections. Repetition of the seismic surveys every two months may improve the identification of the defects and provide a time-lapse seismic study. Synthetic traveltime tomography results indicate the defect position, but fail in recovering its P-wave velocity and size. Acquiring seismic data once the dam reservoir is filled will provide more insights about the potential of this method.
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| 25. |
- Åhs, Magnus, et al.
(författare)
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Application of a hygrothermal model to predict temperature and humidity development in the VeRCoRs benchmark case
- 2016
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Konferensbidrag (refereegranskat)abstract
- This study presents a multiphysics model developed to predict the internal temperature and moisture development in a concrete reactor containment at an early age. The work is a part of the benchmark study, VeRCoR, provided by EDF. The model was applied on an experimental reactor containment mock-up erected in the vicinity of Paris. The 3D geometry was provided from VeRCoRs. The model includes concrete hydration, heat release, chemical moisture binding, and a moisture transport model with relative humidity as a driving potential. Results from the simulation was compared with temperature sensors located in the mock-up. The model was found to be able to predict the temperature development at early age. There was no possibility to compare the relative humidity because of lack of humidity sensors.
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| 26. |
- Åhs, Magnus, et al.
(författare)
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Modelling creep in a pre-stressed mock-up reactor containment : The VeRCoRs 2018 benchmark case
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this study, a multiphysics model is presented that predicts creep in three months old concrete cylinders subjected to drying. The model includes concrete hydration, and a moisture transport model with relative humidity as the driving potential. These parameters are important to include in order to simulate creep. The model was implemented in the finite element software COMSOL Multiphysics. The calculated axial deformation of the cylinder was compared with measurements performed on an experimental set-up. The model was found to be able to predict the axial deformations with reasonable accuracy. This study is a part of the VeRCoRs 2018 benchmark provided by the Electricité de France, EDF.
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| 27. |
- Åhs, Magnus, et al.
(författare)
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Modelling creep in concrete cylinders subjected to different relative humidity levels–the VeRCoRs 2018 benchmark
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this study, a multiphysics model is presented that predicts creep in three months old concrete cylinders subjected to drying. The model includes concrete hydration, and a moisture transport model with relative humidity as the driving potential. These parameters are important to include in order to simulate creep. The model was implemented in the finite element software COMSOL Multiphysics. The calculated axial deformation of the cylinder was compared with measurements performed on an experimental set-up. The model was found to be able to predict the axial deformations with reasonable accuracy. This study is a part of the VeRCoRs 2018 benchmark provided by the Electricité de France, EDF.
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| 28. |
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