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  • 1.
    Abbasiverki, Roghayeh
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Initial study on seismic analyses of concrete and embankment dams in Sweden2017Report (Other academic)
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  • 2.
    Abbasiverki, Roghayeh
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ahmed, Lamis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. Sweco.
    Analysis of load and response on large hydropower draft tube structures2019Report (Refereed)
    Abstract [en]

    In a reaction turbine, the runner outlet is connected to a diffuser which is called the draft tube. Large hydropower units with large effect and large discharge normally require large dimensions on the waterways. In some large-scale facilities, the total width of the draft tube is so large there is a need for a supporting centre wall in the draft tube. In the Swedish hydropower business, there are several cases where damages or cracks have been reported in the contact between the roof and the supporting centre wall. The most likely reason for cracking between wall and roof is when refilling the draft tube after it has been drained for inspection. A too quick refilling will give an upwards lifting force on the roof that can be larger than the capacity in the joint. There are still uncertainties regarding the risk for a long-term scenario where any operational pattern could give continued crack propagation.

    Vattenfall Hydropower has made an installation with pressure and strain sensors in one of their facilities with a centre wall supported draft tube and a cavity between the roof and the rock cavern. The aim of the project is to get a better understanding on the behaviour of the roof and centre wall during different operational events by evaluating measurements from the draft tube and investigating possible load cases that can create continued crack propagation during operation. In this regard, in this project, the measurements are analysed to discover the different operational patterns and the corresponding effect on applied pressure on draft tube central wall and roof and structure response. A simplified finite element model of the draft tube is demonstrated and the response from the structure due to extracted load patterns is compared with the measurements.

    One-year measurements of the unit operation indicated that unit operates over the whole range with many start/stops. Three major types of operation were: normal operation (working in daytime and downtime at night), continuous operation with no stop and start-stop events with sharp start/stop in the morning and afternoon. The analysis of pressure measurements indicated that the fluid motion in the straight diffuser is turbulent and possibly influenced by vortex formation under the runner. Therefore, the pressure on the right side of the central wall was higher than on the left side.

    The quality of the strain measurements showed to be of insufficient quality and lack of information regarding the set-up. This has given questions on the possibility to get reliable results in the evaluation. Nevertheless, an evaluation has been performed. The evaluation of strain measurements demonstrated higher strain values at the upstream side of the central wall and roof. Moreover, the strain on underside of the roof was higher than on the central wall. Sudden fluctuation during continuous operation and sequence of start/stop were the cases that in long-term may cause damage to the structure due to fatigue problems. The results from finite element model indicated high tensile strength at the upstream side of the straight diffuser, in contact between the roof and the central wall where a crack has been detected in the real structure.

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  • 3.
    Abbasiverki, Roghayeh
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nonlinear Behaviour of Concrete Buttress Dams under High-Frequency Excitations Taking into Account Topographical Amplifications2021In: Shock and Vibration, ISSN 1070-9622, E-ISSN 1875-9203, Vol. 2021, p. 1-22Article in journal (Refereed)
    Abstract [en]

    Concrete buttress dams could potentially be susceptible to high-frequency vibrations, especially in the cross-stream direction, due to their slender design. Previous studies have mainly focused on low-frequency vibrations in stream direction using a simplified foundation model with the massless method, which does not consider topographic amplifications. This paper therefore investigates the nonlinear behaviour of concrete buttress dams subjected to high-frequency excitations, considering cross-stream vibrations. For comparison, the effect of low-frequency excitations is also investigated. The influence of the irregular topography of the foundation surface on the amplification of seismic waves at the foundation surface and thus in the dam is considered by a rigorous method based on the domain-reduction method using the direct finite element method. The sensitivity of the calculated response of the dam to the free-field modelling approach is investigated by comparing the result with analyses using an analytical method based on one-dimensional wave propagation theory and a massless approach. Available deconvolution software is based on the one-dimensional shear wave propagation to transform the earthquake motion from the foundation surface to the corresponding input motion at depth. Here, a new deconvolution method for both shear and pressure wave propagation is developed based on an iterative time-domain procedure using a one-dimensional finite element column. The examples presented showed that topographic amplifications of high-frequency excitations have a significant impact on the response of this type of dam. Cross-stream vibrations reduced the safety of the dam due to the opening of the joints and the increasing stresses. The foundation modelling approach had a significant impact on the calculated response of the dam. The massless method produced unreliable results, especially for high-frequency excitations. The free-field modelling with the analytical method led to unreliable joint openings. It is therefore recommended to use an accurate approach for foundation modelling, especially in cases where nonlinearity is considered.

  • 4.
    Ansell, Anders
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Service-life extension of tunnel shotcrete subjected to steel fibre corrosion2022Conference paper (Refereed)
  • 5.
    Ansell, Anders
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. Sweco Energuide, Hydro Power & Dams, Stockholm, Sweden.
    Guarin, Alvaro
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Laboratory investigation of steel fibre reinforced sprayed concrete using a computed tomography method2018In: Eight International Symposium on SPRAYED CONCRETE - Modern Use of Wet Mix Sprayed Concrete for Underground Support, 2018, p. 24-38Conference paper (Refereed)
    Abstract [en]

    A laboratory method for investigation of cored samples of steel fibre reinforced sprayed concrete (shotcrete) is described. A pilot study on computed tomography (CT) has been conducted, with focus on how the technique can be used for non-destructive testing where the cores remain intact after scanning and evaluation. The CT method require advanced integrated equipment for X-ray scanning and image detection, together with a computerized visualization system that can reproduce a threedimensional virtual, transparent model of the studied object. The method is well suited to describe orientation and distribution of steel fibres within the concrete. Interfaces between rock-concrete and concrete-concrete, between layers of differentsequences ofspraying, can also be identified. The results from the CT investigations can be presented as qualitative data that in 3D shows locations of steel fibres, aggregates, etc., and also as quantitative data showing relative distributions of cement paste, aggregates, steel fibres and voids, which is here demonstrated by a selection of examples. The method is well suited for practical analysis of sprayed concrete in situ specimens and it is recommended that it is established as a standard method for special inspections and performance evaluation of rock support in tunnels and subspace structures.

  • 6.
    Ansell, Anders
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Strömberg, Larissa
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Durability of shotcrete tunnel linings due to steel fibre corrosion in cracks2020Conference paper (Refereed)
    Abstract [en]

    Steel fibre reinforcement in homogenous, intact, wet-mix shotcrete show an excellent durability against corrosion. The alkaline concrete environment gives good protection but the relatively thin shotcrete layers may crack due to shrinkage and other deformations. Durability requirements today often demands service-life of more than 100 years, which is not realistic with a maintained load-bearing capacity. Special measures must therefore be taken in the design of shotcrete rock support, such as addition of extra amount of fibres if the shotcrete is cracked or increased structural thickness, which is here demonstrated with examples. Due to the complex situation with requirements on service-life, climate impact and cost-efficiency, the design of future shotcrete supports will be optimized based on life cycle and life cycle cost analyses.

  • 7.
    Berrocal, Carlos G.
    et al.
    Chalmers University of Technology, 41296, Gothenburg, Sweden; Thomas Concrete Group AB, 41254, Gothenburg, Sweden.
    Fernandez, Ignasi
    Chalmers University of Technology, 41296, Gothenburg, Sweden.
    Löfgren, Ingemar
    Chalmers University of Technology, 41296, Gothenburg, Sweden; Thomas Concrete Group AB, 41254, Gothenburg, Sweden.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. Vattenfall AB, 16992, Stockholm, Sweden.
    Rempling, Rasmus
    Chalmers University of Technology, 41296, Gothenburg, Sweden; NCC AB, 41250, Gothenburg, Sweden.
    Strain and Temperature Monitoring in Early-Age Concrete by Distributed Optical Fiber Sensing2023In: Proceedings SynerCrete 2023 International RILEM Conference on Synergising Expertise towards Sustainability and Robustness of Cement-based Materials and Concrete Structures, Springer Nature , 2023, Vol. 43, p. 913-924Conference paper (Other academic)
    Abstract [en]

    In the way towards a carbon neutral construction industry, the partial substitution of cement clinker by alternative binders is becoming increasingly popular in the design of low-carbon concrete mixes. However, as new concrete mixes are developed, the parameters governing the risk of early-age cracking arising from restraint forces due to thermal and shrinkage deformations need to be investigated for each mix. This paper reports the results of a field test in which distributed optical fiber sensors (DOFS) were used to monitor strain and temperature in two large-scale prisms cast against the ground. One of the specimens was cast with a reference concrete mix with CEM I whereas in the other mix cement was partly replaced by fly ash. After casting, mineral wool was used to insulate the specimens in order to reproduce realistic conditions in large mass concrete elements. Temperature measurements enabled a direct comparison of the heat generated by each mix as well as the estimation of the strength development. Strain measurements, on the other hand, gave an indication of the variation of the degree of restraint along the height of the specimens. Using available models for concrete creep, the tensile stresses along the specimens were calculated at different heights and compared to the expected tensile strength in order to assess the crack risk. After removing the insulation, measured strains exhibited a strong dependence on external temperature variations. The test results proved useful to analyse the early-age behaviour of concrete.

  • 8. Blomdahl, Johan
    et al.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Minimiarmering i vattenkraftens betongkonstruktioner - Förstudie2016Report (Other academic)
  • 9.
    Bryne, Lars Elof
    et al.
    Vattenfall R&D.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Sjölander, Andreas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Load-bearing capacity for shotcrete of various fibre types and curing sequences2022Conference paper (Refereed)
  • 10.
    Bryne, Lars Elof
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. Vattenfall AB R&D, Älvkarleby, Sweden.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. Vattenfall AB R&D, Älvkarleby, Sweden.
    Expansion-joints in concrete dams2023In: 91st Annual ICOLD Meeting, Gothenburg, Sweden, 13-14 June 2023: Management for Safe Dams / [ed] Erik Nordström, Stockholm, 2023Conference paper (Refereed)
    Abstract [en]

    Hydro power facilities in Sweden are in general exposed to large temperature variations betweensummer and winter, high moisture levels and high hydrostatic pressure on water retaining structures.In concrete structures with insufficient properties these factors co-operate and can result indegradation by e.g., frost action, erosion, leaching and stresses that can aggravate leakage of waterand further degradation or cracking of the concrete material. In concrete dams and hydro power plants different kind of joints are installed. Cold joints anddilatation joints are two common types. Dilatation joints must be designed and constructed sothey are both water retaining and flexible enough to follow thermal movements of the concretewithout rupturing. A joint that is not well constructed with a good performance can jeopardize thedam safety for a hydro power facility with uncontrolled leakage, ice-formation, degradation orproblematic erosion on the down-stream side. A laboratory study of concrete from an dilatation joint has been performed in this project. Thestudied materials are taken from a larger concrete slab of a spillway sill of a concrete dam. Thescope of the project has been to study the characteristics of the concrete around the water stop anddilatation joint. The goal was to learn more about the mechanisms behind the degradation andleaking of expansion joints.

  • 11.
    Enzell, Jonas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Sjölander, Andreas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    FOI, Totalförsvarets forskningsinstitut.
    Modellförsök stärker betongdammars säkerhet2023In: Bygg och Teknik, ISSN 0281-658X, E-ISSN 2002-8350, Vol. 115, no 6Article in journal (Other (popular science, discussion, etc.))
    Abstract [sv]

    Dammhaverier är mycket ovanliga och därför är kunskapen om brottförloppet vid ett potentiellt dammbrott begränsad. Uppstår brottet utan förvarning, eller finns tidiga tecken på allvarliga problem? Hur utvecklas brottsbräschen under brottförloppet? Detta är frågor som blivit än mer aktuella efter tre internationella dammhaverier under 2023. För att söka svar har en serie skalmodellförsök utförts där haverier av betongdammar simuleras. En viktig parameter vid säkerhetsbedömningen av en betongdamm består i att utvärdera dess stabilitet. Förenklat görs dettag enom att jämföra om dammkroppens vikt är tillräcklig för att stå emot lasten från vattnets tryck. Traditionellt beaktas enbart en mindre del av en betongdamm när dess stabilitet utvärderas men de nya försöken indikerar att det vore eftersträvansvärt att undersöka hela dammen samtidigt eftersom lasten fördelas mellan konstruktionsdelarna. Många betongdammars tillstånd övervakas idag genom automatiska mätningarav till exempel vattenstånd, förskjutningar och grundvattentryck. Dock finns det ingen standardiserad metod för att definiera larmgränser,vilket detta projekt syftar till att utveckla i framtiden.

  • 12.
    Enzell, Jonas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hellgren, Rikard
    Svenska kraftnät, Norrköping, Sweden.
    Malm, Richard
    FOI Swedish Defence Research Agency, Stockholm, Sweden.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Sjölander, Andreas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Realistic numerical simulations of concrete dam failures2023Conference paper (Refereed)
    Abstract [en]

    Dam failures may have catastrophic consequences, including the release of largeamounts of water, significant property damage, and loss of life. However, safety assessments ofconcrete gravity and buttress dams often rely on simplified methods that do not consider the interactionbetween monoliths, the shape of the foundation or the presence of stiff abutments. Numericalmodeling can be a valuable tool for analyzing the stability of these dams, but it can bedifficult to validate these models due to a lack of documented dam failures. This paper presentsthe results of a numerical study examining the ability of dynamic finite element analyses to simulatedam failures. The study used the results from a series of physical model tests as a case studyfor validation. It was found that the numerical model was able to accurately reproduce the failuremode and breach development observed in the physical model tests and capture the effect of theloading rate on the failure mode and time for the failure to develop. Simulations were also performedin prototype scale to verify that the model tests were representative of a real dam failure.Further research is needed to determine the reliability of the numerical models under differentloading conditions and in realistic geological settings. However, these findings suggest that numericalmodeling can be a valuable tool for analyzing the stability of concrete gravity and buttressdams and predicting the development of failures.

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  • 13.
    Enzell, Jonas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Methods for assessing the failure process of concrete dams founded on rock2021Report (Other academic)
  • 14.
    Enzell, Jonas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Sjölander, Andreas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    Department for Weapons, Protection and Security, FOI Swedish Defence Research Agency, Olof Arrhenius väg 31, 137 94 Norra Sorunda, Sweden.
    Physical Model Tests of Concrete Buttress Dams with Failure Imposed by Hydrostatic Water Pressure2023In: Water, E-ISSN 2073-4441, Vol. 15, no 20, article id 3627Article in journal (Refereed)
    Abstract [en]

    Although the failure of a concrete dam is a complex and highly dynamic process, the current safety assessments of concrete gravity and buttress dams rely on a simplified 2D stability analysis, which neglects the load redistribution due to 3D monolith interactions and the valley shape. In addition, the estimation of breach parameters in concrete dams is based on assumptions rather than analyses, and better prediction methods are needed. Model tests have been conducted to increase the understanding of the failure behavior of concrete dams. A scale model buttress dam, with a scale of 1:15, consisting of 5 monoliths that were 1.2 m in height and 4 m in width, was constructed and loaded to failure using water pressure. The model dam had detachable abutment supports and shear keys to permit variations in the 3D behavior. The results showed that the shear transfer was large between the monoliths and that the failure of a single dam monolith is unlikely. A greater lateral restraint gives not only a higher failure load but also a better indication of impending failure. These findings suggest that the entire dam, including its boundary conditions, should be considered during a stability assessment. The results also suggest that the common assumption in dam safety codes that a single monolith fails during flooding analysis is not conservative. The dataset obtained provides a foundation for the future development of dam-monitoring alarm limits and for predictive models of dam-breaching processes.

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  • 15.
    Friborg, J
    et al.
    Guideline Geo.
    Emilsson, J
    Guideline Geo.
    Nordström, Erik
    Vattenfall, Sweden.
    Gustavsson, J
    Guideline Geo.
    Securing hydropower production using airborne Gpr2022Conference paper (Refereed)
    Abstract [en]

    Hydropower is an essential source of renewable energy. To secure power production in cold climates, it is of vital importance to continuously collect information regarding ice build-up around the power plant. The amount of ice, and the quality of the same, can cause significant loss in power production. Ice loads on dam structures are complicated to model and predict without plenty of data points. Traditionally this is performed by foot and using drilling, which is not only a safety issue but usually delivers too few data points to obtain an accurate model of the ice load. With recent developments of airborne GPR equipment, hazardous areas can be investigated safely and efficiently. Furthermore, in comparison to traditional methods airborne GPR collects vast amounts of data points, thus helping create better and more stable models for ice-loads. This paper covers a study from around a hydropower plant in northern Sweden. The study discusses the pros and cons of using air borne GPR equipment for securing hydropower production in cold climate areas.

  • 16.
    Gasch, Tobias
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hassanzadeh, Manouchehr
    Lund University, Division of Building Materials.
    Non-linear analyses of cracks in aging concrete hydro power structures2016In: Dam Engineering, ISSN 0958-9341Manuscript (preprint) (Other (popular science, discussion, etc.))
    Abstract [en]

    The concrete structures at Swedish hydro power facilities were built during the early to mid-20th century and many of them are starting to exhibit age related wear and deterioration. It isimportant to ensure the integrity of these concrete structures from a dam safety perspectiveand also to secure a safe operation of the power facility in the future. With the latter in mind,this paper aims to study the concrete structures that house the power generating machinery ofthe facility, especially the parts close to the generator where the loads from the power unit aresupported. Cracks observed in these structures will reduce its stiffness, which affects theoperation of the rotating machinery. This paper presents and discusses some generalconsiderations and loads that are of importance for this type of structures and highlights sometypical cracks that have been observed in Swedish hydro power facilities. To complement thisdiscussion, a case study is presented of a hydro power facility where cracks have been foundin the concrete support structure of the power unit, especially at the interconnections betweenthe unit and the concrete. The most likely cause of these cracks are investigated through nonlinearfinite element analysis considering mechanical loads as well as physical loads such asdrying shrinkage and temperature variations. It is concluded that the long-term physicalloading is the most probable cause of the observed cracks. However, the operation of thepower unit and changes in its operational pattern can cause further propagation of thesecracks. Finally, suggestions on possible enhancement of the analysis methods used in the casestudy are proposed and discussed for further studies of this type of concrete structures.

  • 17.
    Gasch, Tobias
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hassanzadeh, Manouchehr
    Lund University, Division of Building Materials..
    Non-linear analyses of cracks in aging concrete hydro power structures2016In: Dam Engineering, ISSN 0958-9341, Vol. 26, no 3, p. 1-26Article in journal (Refereed)
    Abstract [en]

    The concrete structures at Swedish hydro power facilities were built during the early to mid-20th century and many of them are starting to exhibit age related wear and deterioration. It isimportant to ensure the integrity of these concrete structures from a dam safety perspectiveand also to secure a safe operation of the power facility in the future. With the latter in mind,this paper aims to study the concrete structures that house the power generating machinery ofthe facility, especially the parts close to the generator where the loads from the power unit aresupported. Cracks observed in these structures will reduce its stiffness, which affects theoperation of the rotating machinery. This paper presents and discusses some generalconsiderations and loads that are of importance for this type of structures and highlights sometypical cracks that have been observed in Swedish hydro power facilities. To complement thisdiscussion, a case study is presented of a hydro power facility where cracks have been foundin the concrete support structure of the power unit, especially at the interconnections betweenthe unit and the concrete. The most likely cause of these cracks are investigated through nonlinearfinite element analysis considering mechanical loads as well as physical loads such asdrying shrinkage and temperature variations. It is concluded that the long-term physicalloading is the most probable cause of the observed cracks. However, the operation of thepower unit and changes in its operational pattern can cause further propagation of thesecracks. Finally, suggestions on possible enhancement of the analysis methods used in the casestudy are proposed and discussed for further studies of this type of concrete structures.

  • 18.
    Hassanzadeh, Manouchehr
    et al.
    Lund University, Building Materials.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Analysis of Displacements and Crack Formations in Foundations for Hydropower Generators2012Conference paper (Refereed)
    Abstract [en]

    A rather extensive program for improvement of the Swedish hydropower plants is ongoing. The aims are to secure future production and to maintain and further develop an already high dam safety. In connection with earlier work, which dealt with assessment of an existing buttress dam where a non-linear finite element model was applied to determine the cause of the observed cracks. The results showed that the non-linear finite element method is a powerful tool to determine the structural behaviour of large concrete structures. The study in this paper is a continuation of the previous project, aiming at applying the method to other parts of dam structure such as foundation supporting the generator (stator and rotor), rotor spider, turbine shaft, spiral casing, turbine and draft tube.

    The hydropower plant, which is studied, was constructed in the early forties. During the inspection, structural damages (cracks) were discovered around some of the stator and rotor spider supports. The cracks were believed to be related to the function of the stator supports and to new patterns of generator operation. In earlier times, the generators ran continuously, while nowadays there are many stops and starts, some times even several times during one day. The purpose of this study is to illuminate the complex stress conditions in the generator foundations of a hydropower plant and to reveal the causes of the stresses and to verify their role in formation of the cracks.

    The structural behaviour of a foundation has been analysed taking into account the transient thermal gradients in combination with dead loads and some of the operational loads imposed to the foundation. A three dimensional non-linear finite element model has been applied in order to analyse formation and propagation of the cracks. The analyses showed that based on the assumption made, the concrete foundation cracks mainly on the outside but also near some of the stator supports due to the combination of mechanical and thermal loads. However, the studied loads cannot explain all of the types of damages that can be found in-situ. It is likely that especially the drying shrinkage may be the one of the reasons for the cracks that has been found near the stator supports and especially the rotor spider supports.

    It is important from a dam safety perspective to determine the causes of the structural cracks that have been found in-situ and also to evaluate the effect of the reduced stiffness due to cracking, since a reduced structural stiffness can result in larger loads imposed on the structure from the magnetic eccentricity and turbine imperfections or alternatively lead to a fatigue failure of for instance the reinforcement.

  • 19.
    Hellgren, Rikard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Enzell, Jonas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Estimating the ice loads on concrete dams based on their structural responseManuscript (preprint) (Other academic)
    Abstract [en]

    In the assessment of concrete dams in cold climate, it is common that the theoretical stability becomes insufficient for load cases that includes ice loads. However, the magnitude and return period of these ice loads have a high degree of uncertainty.  This study estimates the magnitude of ice loads on eight concrete dam monoliths using measurements of their displacement from 29 winters. In the displacement signals, events are identified and assumed to be caused solely by ice loads. The observed displacement during an event is interpreted as an ice load using a load-displacement relationship derived from FE simulations of each dam. These simulations show that ice loads of the magnitudes given in design guidelines and recorded in previous measurements would significantly affect the structural response of the studied dams. However, only small traces of ice loads can be found in the observed responses of the studied dams. The estimated ice loads are significantly lower than the ice loads recorded in traditional ice load measurements. These results indicate that the average magnitude of ice load on an entire monolith is significantly lower than the measured local pressures. This would imply that ice loads may be a smaller concern regarding the dam safety than previously believed.

  • 20.
    Hellgren, Rikard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Enzell, Jonas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Estimating the Ice Loads on Concrete Dams Based on Their Structural Response2022In: Water, E-ISSN 2073-4441, Vol. 14, no 4, article id 597Article in journal (Refereed)
    Abstract [en]

    In the assessment of concrete dams in cold climate, it is common that the theoretical stability becomes insufficient for load cases that include ice loads. However, the magnitude and return period of these ice loads have a high degree of uncertainty. This study estimates the magnitude of ice loads on eight concrete dam monoliths using measurements of their displacement from 29 winters. In the displacement signals, events are identified and assumed to be caused solely by ice loads. The observed displacement during an event is interpreted as an ice load using a load-displacement relationship derived from FE simulations of each dam. These simulations show that ice loads of the magnitudes given in design guidelines and recorded in previous measurements would significantly affect the structural response of the studied dams. However, only small traces of ice loads can be found in the observed responses of the studied dams. The estimated ice loads are significantly lower than the ice loads recorded in traditional ice load measurements. These results indicate that the average magnitude of ice load on an entire monolith is significantly lower than the measured local pressures. This would imply that ice loads may be a smaller concern regarding dam safety than previously believed.

  • 21.
    Hellgren, Rikard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Fransson, Lennart
    Luleå University of Technology.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Westberg Wilde, Marie
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Measurement of ice pressure on a concrete dam with aprototype ice load panelManuscript (preprint) (Other academic)
    Abstract [en]

    This paper presents the development and installation of a prototype ice load panel andmeasurements of ice load from February 2016 to February 2018 at the Rätan hydropower damin Sweden. The design of the 1x3 m2 panel enabling direct measurement of ice pressure on theconcrete surface is based on previous experience from similar measurements with sea ice.Important features of the design are sufficient height and width to reduce scale effects and tocover the ice thickness and variations in water level. The Rätan dam was chosen based onseveral criteria so that the ice load is considered to be reasonably idealized against the damstructure.For the three winters 2016, 2016/2017, 2017/2018, the maximum ice load recorded was 161kN/m, 164 kN/m and 61 kN/m respectively. There were significant daily fluctuations duringthe cold winter months, and the daily peak ice loads showed a visual correlation with the dailyaverage temperature and with the daily pattern of operation of the power station with itscorresponding water level variations

  • 22.
    Hellgren, Rikard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Modeller för övervakning av betongdammar: Energiforskrapport 2019:5802019Report (Other academic)
    Abstract [en]

    In the field of dam surveillance, alert and alarm values are used for error detection to notify about the discovery of a potential dam safety risk. Alarm values are used to notify that a dangerous behavior have been reached. Alert values (warnings) are used to notify that the measured data is out of the expected range. Dam surveillance can thereby be considered as a classification problem where every measured response should be classified as safe or unsafe, or alternatively as expected or unexpected. Dangerous behavior implies that the safety of the dam may be compromised (e.g. the coefficient of safety may be surpassed), while an unexpected value occurs when the dam no longer acts according to the predicted behavior based on current conditions. Such a discrepancy does not necessarily mean that the dam safety is compromised, but could indicate that the dam is damaged.In order to determine the expected behavior, some type of prediction model is required that can predict the dam behavior based on ambient conditions. In this report, the prediction models are defined as either theory-based or empirical. The theory-based models are based on physics with correlation between ambient conditions such as water level and temperatures and the response of the dam. In the empirical models, this coupling is purely empirical without any physical meaning.There are several types of sensors that can be used for dam surveillance. In this report, the instruments commonly used within the field of dam engineering and their expected accuracy are discussed. In addition, the use of different sensors based on their purpose in the surveillance program is discussed where sensors are denoted as detectors or support instruments. The detectors are considered as sensors suitable to be used to monitor a potential failure mode while the purpose of the support instruments is to provide additional information about the dam response or the ambient conditions.Every type of model has unique properties with different pros and cons. It is therefore important to choose the type of model based on the need and purpose of the monitoring or evaluation of the dam response. A finite element model gives good possibilities to interpret the results and find the physical meaning of a specific behavior, but is not as good to give exact predictions. The most advanced empirical models are defined without any physical meaning, but are capable to give precise predictions of the expected response. To choose one type of model over another can thereby be described as choosing between understanding and performance. Luckily, the use of one model does not exclude the use of others. The models based on physics helps us understand and interpret the dam behavior and will therefore always have a use in the dam safety work. It is also the type of model that best can be used to study scenarios during dam failure and thereby to define alarm values. As a compliment to these, the empirical models can be used to give early warnings when the dam behavior is out of the ordinary and is therefore most suited for definition of alert values. These models generally perform better and has smaller deviation than the corresponding theoretical models.The case studies presented in this report shows that the simple empirical models with some physical meaning gives very good predictions of the expected behavior.

  • 23.
    Lagerlund, Johan
    et al.
    Vattenfall Research and Development AB.
    Bernstone, Christian
    Vattenfall AB.
    Viklander, Peter
    Vattenfall Research and Development AB.
    Nordström, Erik
    Vattenfall Research and Development AB.
    Embankment test dam of Älvkarleby: Description of installed defects and their position2022Other (Other academic)
  • 24.
    Lagerlund, Johan
    et al.
    Department of Civil, Environmental and Natural Sources Engineering, Division of Mining and Geotechnical Engineering, Luleå University of Technology, Luleå, Sweden;Vattenfall Research & Development, Civil Engineering, Älvkarleby, Sweden.
    Laue, Jan
    Department of Civil, Environmental and Natural Sources Engineering, Division of Mining and Geotechnical Engineering, Luleå University of Technology, Luleå, Sweden.
    Viklander, Peter
    Vattenfall Vattenkraft AB, Luleå, Sweden;Department of Civil, Environmental and Natural Sources Engineering, Division of Mining and Geotechnical Engineering, Luleå University of Technology, Luleå, Sweden.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Testing of a low-mobility grout material for permeation grouting in embankment dams2023In: Geotechnical Research, E-ISSN 2052-6156, p. 1-11Article in journal (Refereed)
    Abstract [en]

    Embankment dams can be damaged by internal erosion, which ultimately leads to a failure. When internal erosion occurs, finer soil particles from the core soil are washed out. To restore the function of the core, injection grouting can be undertaken. Grouting the core of an embankment dam should be performed with a grout material with characteristics similar to the core soil, such as a low-mobility grout. This type of grout material has similarities to a fine-grained moraine core soil given its stiffness, but it has difficulties permeating the damaged core soil. A modified low-mobility grout material containing gravel, sand, limestone filler, bentonite, plasticizer, air release agent, and water has been tested in the laboratory with focus on permeation. Injection was done on different-sized aggregates. The impact of paste-to-aggregate ratio, grout consistency, maximum grain size of grout material, particle size distribution of injected material, and injection method was tested. Higher paste-to-aggregate ratios, lower viscosity and lower yield strength of the grout material improved the permeation.

  • 25.
    Malm, Richard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Fransson, Lennart
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Westberg Wilde, Marie
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Hellgren, Rikard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Lastförutsättningar avseende istryck2017Report (Other academic)
  • 26.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Evaluation after 17 years of field exposures on cracked steel fibre reinforced shotcrete2017In: Proceedings of XXIII Nordic Concrete Research Symposium in Aalborg, Denmark, 2017, p. 111-114Conference paper (Refereed)
  • 27.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. Vattenfall R&D, Sweden.
    Management for Safe Dams2023Conference proceedings (editor) (Refereed)
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  • 28.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Strategi för förvaltning av inre vattenvägar2021Report (Other academic)
    Abstract [sv]

    Inre vattenvägar i ett vattenkraftverk är vanligtvis svåråtkomliga förinspektion och vissa delar är aldrig inspekterade efter idrifttagning.Många vattenkraftföretag saknar en systematisk förvaltning av de inrevattenvägarna.Föreliggande projekt har därför bestått i att söka beskriva hur ett system förstrategisk förvaltning av de inre vattenvägarna bör vara uppbyggt. Beskrivningaroch exempel är till stora delar generella och bör anpassas efter företagsegnaprocesser, system och rutiner samt till företagets storlek på anläggningsportföljen.De inre vattenvägarna är av tunneltyp, i berg eller betong, och kan vara helt ellerdelvis fyllda med vatten. Beskrivningarna är till stora delar även tillämpbara påbottenutskov med tillhörande tillopps- / utloppstunnel.En viktig del i systemet är dokumentation av vilka anläggningsdelar som ingår,deras uppbyggnad konstruktivt och vilken inbördes konfiguration de har. Det gervägledning både kring vilken access de olika delarna har och hur en avställning förinspektion påverkar driften. I rapporten ges exempel på hur grundläggande ochdetaljerad anläggningsinformation kan sammanställas.Utöver rena tunnelras är det vanligaste scenariot att förändringar i strukturerna ärlångsamma och därför behöver tidigare genomförd tillståndskontroll varasammanställd för att kunna bedöma ev. skadeutveckling. Planeringen avinspektionsintervall måste också baseras på kännedom om status.En plan för, och differentiering av, inspektionsintervall bör byggas upp utifrån enbedömning om vilken risk för produktionsbortfall varje enskild vattenväg utgörp.g.a. problem i densamma. En mycket rudimentär riskanalysmodell baserad påpotentiell konsekvens och bedömd sannolikhet för problem presenteras irapporten. Konsekvenserna baseras på indata gällande enskilda aggregatsproduktionsvärde, vattenvägarnas konfiguration (gemensamma tunneldelar ellerej) och längden på tunnlarna. Sannolikheterna bedöms utifrån ev. identifieradeproblempartier redan från byggtiden, förväntade egenskaper hos ingåendekonstruktionsmaterial efter lång tid, konstaterade svagheter vid inspektioner ochom ev. riskkonstruktioner förekommer i vattenvägen.Intervallen för inspektion måste också baseras på att accessen till de inrevattenvägarna är olika. En grov indelning har gjorts mellan de delar som inrymsmellan intagslucka och sugrörslucka för ett enskilt aggregat och de delar som ärutanför dessa. De förstnämnda omfattas av en liten inspektion vilken kan göras medintervall om 6-12 år. De senare som kan orsaka större produktionsbortfall ellert.om. kräver tillfälliga avstängningar för ev. torrläggning omfattas av en storinspektion. vilka föreslås genomföras med ett intervall om 25-50 år.I rapporten ges slutligen övergripande råd för inspektioner gällande planering,lämpliga kompetenskrav, genomförande, värdering av svagheter och denslutgiltiga rapporteringen.

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  • 29.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Temperaturrelaterade sprickor i vattenbyggnadsbetong: Alternativa metoder för riskreduktion2019Report (Other academic)
    Abstract [sv]

    Betongkonstruktioner inom vattenbyggnad utgörs till stor del av massiva betongkonstruktioner med grova dimensioner. Temperaturutvecklingen som ges av cementets hydratationsprocess ger höga temperaturer inne i konstruktionerna. Mothåll från berggrund och omgivande konstruktioner, såväl som de gradienter som uppstår mellan de grova konstruktionernas inre och yttre delar, ger en risk för sprickbildning främst under avsvalningsskedet. Sprickbildning kan ge kostnader för reparationer men också läckage och beständighetsproblem som följd av detta. Vanligtvis används efterkylning genom installation av kylrör för cirkulerande kylvatten i de grova konstruktionerna, men installationerna kan vara kostsamma.På uppdrag av Vattenfall AB har KTH Betongbyggnad gått igenom befintliga regelverk och standards som reglerar de möjligheter man har att justera andra ingående parametrar för att sänka risken för temperaturrelaterad sprickbildning. Målsättningen i uppdraget har varit att utveckla ett betongkoncept för anläggningsbyggande inom vattenkraft som kan implementeras vid ombyggnationerna av utskovsdammen i Lilla Edet, Göta Älv år 2020. Arbetet har utgjort en förstudien inför projektering och upphandling av arbetena i det anläggningsprojektet.

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  • 30.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Utvärdering efter 17 års fältexponering av sprucken stålfiberarmerad sprutbetong2016Report (Other academic)
    Abstract [sv]

    Rapporten redovisar resultaten från den senaste utvärderingen av en fältexponeringsserie som startades 1997 som en del av författarens doktorandprojekt. Föreliggande utvärdering har finansierats av BeFo och Energiforsk. Stålfibrer har vanligen både syftet att vara sprickfördelande/sprickviddsbegränsande i bruksgränstillstånd  och  att  ge  residualbärförmåga  och  duktilitet  i  brottgränstillstånd.  Studien   har   primärt   inriktats   på   om,   och   under   vilka   förutsättningar,   som   stålfiberkorrosion   riskerar   uppstå   i   sprickzonen.   Ett   vanligt   livslängdskrav   för   anläggningskonstruktioner är 100 år. Fältproverna har exponerats i tre vanligen förekommande miljöer, nämligen vägmiljö (Rv40, Borås), tunnelmiljö (Eugeniatunneln, Stockholm) och älvmiljö (Älvkarleby). De materialparametrar som varierats är sprutbetongtyp (våt-/torrsprutad), fiberlängd, acceleratortillsats och sprickvidder. Samtliga  provplatserna  uppvisar  korrosion  efter  17  års  exponering,  men  i  mycket  begränsad  omfattning  i  älvmiljön.  Korrosionsangreppet  är  kraftigast  vid  Rv40  som  utgör en miljö med kombinationen av hög fuktighet och relativt hög kloridbelastning. Tydligaste påverkan av mixtypen erhölls av prover med långa fibrer som korroderade betydligt  fortare  än  de  kortare  fibrerna  vilket  fortsatt  stärker  vikten  av  förhållandet  mellan  anod  och  katod.  Provernas  sprickvidd  hade  mest  betydelse  för  tiden  till  initiering  av  korrosion,  men  efter  initiering  utvecklas  korrosionen  i  ungefär  samma  hastighet.  Det  finns  en  tydlig  koppling  mellan  en  mer  utvecklad  fiberkorrosion  och  förlust  av  bärförmåga  vilket  blir  särskilt  tydligt  vid  utvärdering  av  bärförmågan  vid  stora  deformationer  (brottsgräns).  För  små  deformationer  (bruksstadium)  och  små  sprickvidder  (0,1  mm)  kunde  en  ökning  av  bärförmågan  ses  som  verkar  bestå  även  efter 17 års exponering.  I Dalälvsproverna noterades en urlakad zon på ca.10 mm efter 17 år. Det konstaterades också att den våtsprutade betongen utan accelerator visade ett något bättre motstånd mot urlakning och den torrsprutade bäst motstånd även om några mm urlakning kunde ses.  Kloridmängderna  i  proverna  vid  Rv40  och  Eugeniatunneln  är  höga  efter  exponeringen  och  i  tunnelmiljön  mycket  höga  vilket  accelererat  den  initierade  korrosionen   kraftigt.   Sannolikt   sker   en   ackumulering   eftersom   betongen   är   regnskyddad inne i tunneln. Det   är   tydligt   att   den   förstörande   utvärderingstekniken   inte   är   optimal   när   korrosionsprocessen gått långt p.g.a. att ”bevismaterialet” inte längre kan identifieras. De  senare  resultaten  där  korrosion  pågått  en  längre  tid  riskerar  att  underskatta  det  verkliga angreppets omfattning. Sammanfattningsvis  kan  konstateras  att  stålfiberkorrosion  i  sprucken  sprutbetong  exponerade  för  kloridutsatta  miljöer  måste  förväntas  uppträda  med  de  vanligast  förekommande  fibertyperna.  Det  är  inte  rimligt  att  anta  100  års  livslängd  med  bibehållen bärförmåga i de provade kloridutsatta miljöerna.

  • 31.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Vägledning för val av ballast i konstruktioner för vattenbyggnad2016Report (Other academic)
    Abstract [sv]

    Det har i vattenbyggnadsbranschen uppdagats ett behov av vägledning vid val av ballast för betongkonstruktioner i Sverige med avseende på risken för alkali-silika-reaktioner (ASR). Då målsättningen för vattenbyggnadskonstruktioner vanligtvis är en livslängd på minst 100 år bör därför valet av ballast vara konservativt tills det finns forskningsresultat som bringat reda på under vilka förutsättningar som ASR uppstår.

    Föreliggande interimistiska vägledning är framtagen inom Energiforsks betongtekniska program vattenkraft i väntan på en nationell vägledning på området.

    I vägledningen rekommenderas att inte högre halt än 15 vikt-% av reaktiva eller potentiellt alkalireaktiva ballastpartiklar ska användas i betong för vattenbyggnadskonstruktioner. Rekommendationen gäller alla konstruktioner som är:

    • dämmande (eller stödjande till dämmande)

    • aggregatnära

    • exponerade för vatten från reservoar

    • del av inre/yttre vattenväg

    • utsatta för nederbörd (Omgivningsklass E2 och E3).

    Rekommendationen gäller även i kombination med användning av lågalkaliska cement, och efter redovisade resultat från funktionsprovning enl. t.ex. RILEM AAR-3.

  • 32.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Bryne, Lars-Elof
    Vattenfall R&D.
    Långtidsexponering av vattenbyggnadsbetong med SCM2021Report (Other academic)
    Abstract [sv]

    Långtidsexponering av betong med inblandning av SCM monterade påfältstationen vid Vattenfall R&D i Älvkarleby.Betongbyggnadsbranschen i Sverige strävar efter att minska klimatbelastningen frånny betong. Det relativt stora CO2-avtrycket från betong beror främst på utsläppensom uppstår vid cementproduktionen. Branschen söker nu minska detta, blandannat genom användning av alternativa bindemedel/tillsatsmaterial och puzzolaner(Supplementary Cementitious Materials, SCM). På den svenska marknaden finns tretyper av SCM tillgängliga kommersiellt. Flygaska från stenkolpulvereldning (importfrån till exempel Tyskland eller Turkiet), mald granulerad masugnsslagg (inhemsk,fransk) och silikastoft från ferrokiselindustrin (Norge).Syftet med projektet är att kunna möjliggöra användning av SCM där så bedömslämpligt och där krav på beständighet kan vidmakthållas under mycket lång tid.Målet med projektet är att genom långtidsexponering av betong med SCM vidfältstationen i Älvkarleby skapa beslutsunderlag kring vilka alternativabindemedel/bindemedelskombinationer som kan vara lämpliga förvattenbyggnadskonstruktioner.För långtidsexponeringen har kiselrik stenkolflygaska (flygaska) och maldgranulerad masugnsslagg (slagg) valts ut. Flygaskan valdes eftersom den ärtillgänglig idag via import och att den är mycket vanlig internationellt idammbyggnadssammanhang. Dessutom är den väldigt potent för att minska riskenför temperaturrelaterad sprickbildning. Slagg produceras åter i Sverige igen efter enlängre tids uppehåll och finns således tillgänglig för överskådlig tid framöver.Fyra olika betongblandningar har använts för att tillverka provkropparna tilllångtidsexponeringen. En traditionell vattenbyggnadsbetong som referens ochdärefter en flygaskabetong med 20% av cementet ersatt med flygaska och tvåslaggbetonger där 20% respektive 35% av cementet ersatts med slagg. För att hagod kontroll på den betong som exponeras har en omfattande karaktärisering avde olika provkropparna genomförts. Syftet är att i de framtida utvärderingarna haen bättre möjlighet till att detektera och förklara eventuella förändringar jämförtmed startläget före exponering. Hållfasthetsegenskaper som tryck-/spräckhållfasthet och dynamisk E-modul har kontrollerats. Vidare har defuktmekaniska förutsättningarna och parametrar som kan påverka en eventuellframtida nedbrytning av frost eller urlakning undersökts genom analys avbetongens kapillaritet, vattenmättnadsgrad vid start, karaktärisering avluftporsystemet och traditionell frostprovning med den s.k. Boråsmetoden. I tillägghar även struktur- och kemanalyser gjorts på tunnslipsprover och betong för attbelägga startläget före exponering.Proverna sitter sedan hösten 2020 monterade vid fältstationen i Älvkarleby vidVattenfall R&D. Ungefär halva provet exponeras i luft och halva nere i älven. Detfinns provkroppar för uttag av borrkärnor till minst tre framtida tillfällen beroendepå omfattning. Det rekommenderas att första utvärdering görs tidigast om 5 år,men kanske ännu hellre efter ytterligare tid.

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  • 33.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Eriksson, Daniel
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Inventering av inre vattenvägsbesiktningar2019Report (Other academic)
    Abstract [en]

    The water is transported by the waterways from the reservoir, past the dam and further downstream in a hydropower station. Generally, the waterways can be categorized to be either of channel-type or tunnel-type. The waterways of tunneltype include a number of different structures such as intakes, headrace tunnels, penstocks, intake sumps, spirals, draft tubes, surge shafts, surge galleries and tailrace tunnels. These structures are usually either fully or partially filled with water, which means that they in many cases are hard to inspect. Moreover, it is seldom financially justifiable to drain the tunnels solely to perform an inspection due to the loss of energy production that this measure entails. However, in connection to stoppage of the energy production to repair, inspect or replace some of the energy-producing parts, an opportunity to inspect the waterways of tunneltype is usually given.

    In this study, a review of documentation from inspections of waterways of tunneltypes has been performed on behalf of Energiforsk to improve the state of knowledge regarding common damage types and deterioration mechanisms in this type of waterways. The collection of data has been performed by inquiring data from representatives of the utility companies in the steering committee of the research program for concrete in hydropower at Energiforsk. The obtained material includes both reports from inspections as well as compilations of observed damage in the waterways for a total of 53 different hydropower stations in Sweden.

    From the analysis of the obtained material in this study, it could be concluded that erosion was the most common type of damage observed in waterways of tunneltype if all types of such structures are considered. However, the results become a bit different if the different types of structures are studied individually, even though erosion often is observed to be one of the most commonly observed damage types. Previous research has, however, shown that an observed damage often is a consequence of a series of deterioration mechanisms that together cause a degradation of the material. Therefore, it is hard to isolate one single deterioration mechanism that is the only reason why erosion is the most commonly observed damage type in waterways of tunnel-type. Furthermore, it could be concluded that the documentation of performed inspections generally is inadequate at the utility companies and consequently also the documentation of observed damage and defects in the waterways. It should, however, be noticed that all companies stated that they have performed inspections but that the documentation from these is either missing or hard to find.

    With results from the study in mind a need for improvement in the management of the inner waterways is obvious. Especially regarding the knowledge on the status of long headrace and tailrace tunnels in rock with different degree of support. For facilities with common head-/tailrace tunnels for several units, the consequences of a larger failure could be substantial in terms of financial losses from no production. It is recommended to develop a strategy for management of inner waterways.

  • 34.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hassanzadeh, Manouchehr
    Sweco.
    Inblandning av flygaska i vattenbyggnadsbetong2018Report (Other academic)
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  • 35.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hassanzadeh, Manouchehr
    SWECO.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ekström, Tomas
    AFRY.
    Janz, Mårten
    AFRY.
    Structural safey of cracked concrete dams2019Report (Other academic)
    Abstract [en]

    Cracks and cracking in concrete dams can give a need to determine the current status from a dam safety perspective and an estimation on remaining service-life taking the cracks in to consideration. A comparison between the current status and the formal requirements should be made. Condition control is a prerequisite to define the current status and future development and to do this there is a need for knowledge on what type of cracks has occurred and the reason for cracking. To do this there is a need to combine observations, sampling, measurements and theoretical models/ analysis. A previous project within Dam Safety Interest Group (DSIG) resulted in a seven- step-method to analyse cracked concrete dams [1] and the current work is taking this forward to adapt the methodology to Swedish conditions. The goal has been to develop a Swedish guideline to define status and both current and future safety level for a cracked concrete dam with the purpose to create a uniform and reliable methodology for condition control and guidance for planning of measures. The disposition of the report is based on a management process with the parts REQUIREMENTS-INVESTIGATIONS-ANALYSIS-MEASURES and in the report also with REFERENCE PROJECTS exemplifying the recommendations given in the report. Recommended requirements for concrete dams can be found in the Swedish power industry guideline RIDAS [3], [4], with focus on water-tightness, stability, load-bearing capacity and limited deformations. Investigations is best performed stepwise from a visual inspection to a more or less detailed investigation with sampling depending on how unclear the conditions are regarding mechanical properties, crack extent, reason for cracks etc. The results are commonly used later when analysis is performed and therefore it is preferred to plan them in cooperation with the person that will do the analysis later.Analysis can be anything from simple behavior models via analytical calculations to advanced numerical simulations. The purpose with the analysis is to investigate if the dam fulfills the requirements. The results can also be used to suggest further investigations, monitoring or strengthening measures. Measures are taken when the deviation from the requirements are not acceptable (now or in the future). It is often a matter of reducing the load, slow down the development or increase/restore the performance. Surveillance with planned inspections, or monitoring, can be used for evaluating any crack propagation and is sometimes selected instead of a physical measure. The compilation of reference projects shows that a common reason for critical cracks often origins from movement due to seasonal temperature variations. Insulation of the dam body to minimize the impact from this is effective. Indoors also cracking from shrinkage is common. Many of the cases have the cause for cracking and damages from frost or ASR. Generally, it is also common with cracks from the time of construction that will not develop further.

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  • 36.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hassanzadeh, Manouchehr
    Lund University, Building Materials.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ekström, Tomas
    Janz, Mårten
    Strukturell säkerhet hos spruckna betongdammar2019Report (Refereed)
  • 37.
    Nordström, Erik
    et al.
    Sweco Energuide AB.
    Krogh, Peter
    Sweco Energuide AB.
    Nilsson, Ola
    Sweco Energuide AB.
    Sjödin, Gunnar
    Vattenregleringsföretagen.
    Stenberg, Rickard
    Vattenregleringsföretagen.
    Hautakoski, Marcus
    Vattenregleringsföretagen.
    Upgrading of the Lossen and Ransaren dams in Sweden2015Conference paper (Refereed)
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  • 38.
    Nordström, Erik
    et al.
    Vattenfall, Sweden.
    Löfgren, Ingemar
    Thomas Concrete Group, Gothenburg, Sweden.
    Berrocal, Carlos Gil
    Thomas Concrete Group, Gothenburg, Sweden.
    Klimatförbättrad vattenbyggnadsbetong utan kylbehov2022In: Bygg & teknik, ISSN 0281-658X, no 6Article in journal (Other (popular science, discussion, etc.))
    Abstract [sv]

    Sedan 2021 pågår byggfasen i ett projekt med fokus på flödesanpassning och delförnyelse av utskovsdammen vid Vattenfalls anläggning Lilla Edet i Göta älv. Till den nya dammdelen kommer cirka 8000 m3 betong att användas under uppförandet. För att minska koldioxidavtrycket från den betong som ska användas och för att reducera risken för temperaturrelaterad sprickbildning har en klimatförbättrad betong med mindre cement utvecklats.

  • 39.
    Nordström, Erik
    et al.
    Vattenfall R&D, Sweden.
    Löfgren, Ingemar
    Thomas Concrete Group, Gothenburg, Sweden.
    Berrocal, Carlos Gil
    Thomas Concrete Group, Gothenburg, Sweden.
    Larsson, Andreas
    Vattenfall Hydro, Trollhättan, Sweden.
    Wolfsborg, Romanas
    Vattenfall Hydro, Stockholm, Sweden.
    Climate enhanced concrete and eliminated need for post cooling in the new Lilla Edet spillway dam, Sweden2023In: 91st ICOLD Annual MeetingSymposium 13–14 June, 2023 Gothenburg, Sweden: Management for Safe Dams / [ed] Erik Nordström, Stockholm, 2023, p. 1380-1389Conference paper (Refereed)
    Abstract [en]

    Dam safety measures on the Vattenfall hydropower facility Lilla Edet, in Sweden are, ongoing by replacing parts of the old spillway dam from the 1920s to increase discharge capacity. A climate enhanced concrete without needs for any post-cooling to avoid thermal cracking has been developed for the project. A series of tests from initial laboratory tests via development of a production mix and a full-scale mock-up preceded the construction works on site. Increase of the maximum aggregate sizes from today’s commonly used 27 mm up to 45 mm was introduced to reduce the cement content. Basic tests to verify fresh properties, air void content, strength development, shrinkage etc. was done for a series of different supplementary cementitious materials before selecting fly ash from combustion of pulverized hard coal (PFA) as cement replacement. Examination of the durability aspects like freeze-thaw and carbonation resistance by accelerated test showed no or limited impact on the properties. Development and optimization of the production mix, with use of locally available materials, was done in cooperation with the concrete supplier. The mock-up tests included two large size beams, one with reference concrete and one with the developed concept concrete. Representative reinforcement (dimensions and spacing) was installed, a full-scale concrete pump used and workers from the project executed the casting. The outcome was successful without blockage during pumping, no honeycombing and happy workers. By using installed gauges and optic fibers, early age behavior in terms of temperature and strain development was measured to be able to estimate the risk for thermal cracking. The concept concrete showed to give a substantially reduced riskfor early age thermal cracks in comparison to the reference concrete. With support from the investigations, a decision to deviate from accepted levels of cement replacement in standards was taken. This was possible since the concrete concept proved to fulfill requirements on expected service-life and robustness during construction without cost increase. By using fly ash from combustion of pulverized hard coal as cement replacement, a reduction of the CO2-emissions by almost 30% has been possible and the need for post-cooling has been eliminated completely.

  • 40.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Blomdahl, Johan
    Sweco.
    Tornberg, Robert
    Sweco.
    Nilsson, Carl-Oscar
    Uniper.
    Optimization of dam monitoring for long concrete buttress dams2015Conference paper (Other academic)
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  • 41.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hassanzadeh, Manouchehr
    Sweco.
    Ekström, Tomas
    ÅF.
    Janz, Mårten
    ÅF.
    Guideline for structural safety in cracked concrete dams2019In: Sustainable and safe dams around the world : proceedings of the ICOLD 2019 symposium, (ICOLD 2019), June 9-14, 2019, Ottawa, Canada = Un monde de barrages durables et sécuritaires : publications du symposium CIGB 2019, Juin 9-14, 2019, Ottawa, Canada, CRC Press, 2019, p. 1681-1696Conference paper (Refereed)
    Abstract [en]

    Several concrete dams show cracking, and their condition and remaining service

    life must be determined. Assessment and service life prediction of cracked dams should include an investigation to determine the cause and consequences of cracks. Cracks can be caused by different mechanisms, which also may act together. Some mechanisms act during a short period of time, e.g. in the beginning after construction, while other mechanisms may influence the dam during the whole service-life. Therefore, it is important to combine observations, measurements, laboratory tests and theoretical analyses investigating the causes of the cracks, their future development and the influence they may have on the performance of the dam. Lessons learned and knowledge concerning crack propagation in concrete and rock, general material engineering, durability concerns caused by cracks, structural analysis issues connected to cracks, field measurements and design of remedial measures has been compiled in a Swedish guideline. The guideline highlights issues that should be looked for in inspections and contains a methodology to determine the residual strength and serviceability of cracked concrete dams and how to review dam safety criteria’s. This in turn will provide the dam owner with a better means to manage and prioritize rehabilitation and maintenance work.

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  • 42.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Ligier, Pierre-Louis
    Lier, Öyvind
    Betongdammars brottförlopp2015Report (Other academic)
  • 43.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Rosenqvist, Martin
    ÅF.
    Sjödin, Gunnar
    Vattenregleringsföretagen.
    Hautakoski, Marcus
    Vattenregleringsföretagen.
    Field investigations on the risk for ASR when using potentially reactive aggregates and low alkali cements: Results after 50 years in Sweden2013Conference paper (Refereed)
    Abstract [en]

    The adverse effects from reactions of reactive aggregates in concrete dams are well known worldwide. The mechanisms ruling alkali silica reactions (ASR) are partly but not fully understood. A majority of the Swedish concrete dams are so far considered to be protected from ASR due to the common use during the 50:s, 60:s and 70:s of the Swedish low alkali cement Limhamn LH. Today there is a discussion if it still is possible to develop ASR after very long time in dams with reactive aggregates and use of low alkali cement. Via selection of seven facilities in the Swedish alpine area, where reactive aggregates are common, the current paper is aiming to compile experiences from almost 50 years of exposure. In the paper two examples on ASR in spite of use of low alkali cement are shown.

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  • 44.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Tornberg, Robert
    Sweco.
    Kamanga, Romas
    Zesco.
    Management of ASR affected spillway structures at Kafue Gorge, Zambia2019Conference paper (Refereed)
    Abstract [en]

    The Kafue Gorge dam along Kafue River in Zambia was commissioned in 1971. In 1988 one of the spillway gates was jammed due to concrete expansion. Measures were taken, but signs of expansion and cracking continued. After rehabilitation works on one of the spillway gates in 2011 five stop-logs were stuck in position due to concrete expansion. In 2012, ZESCO and SWECO performed an in-depth assessment of the spillway structure with crack mapping and core sampling. Extensive cracking on the upstream side of the spillway piers with crack widths of up to 30 mm was found under water. Concrete analysis verified ongoing ASR. Numerical simulations on the behavior of the dam (with major cracks and ASR-expansion) showed that there was a need for stabilizing measures. SWECO designed remedial measures to restore full integrity of the dam and resolve the problem with the jammed stop-logs that caused reduced discharge capacity. During 2019 post-tensioned tendons are installed to ensure a monolithic behavior of the structure and improve the stability. All major cracks will be sealed to reduce the contact area of concrete and water. Finally, the jammed stop-logs will be removed to restore the discharge capacity of the spillway.

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  • 45.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Tornberg, Robert
    Sweco.
    Kamanga, Romas
    Zesco.
    Management of ASR-affected spillway structures at Kafue Gorge, Zambia2019Conference paper (Other academic)
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  • 46.
    Rosenqvist, Martin
    et al.
    Vattenfall Research & Development, Älvkarleby.
    Nordström, Erik
    Sweco Infrastructure, Gävle, Sweden.
    Hassanzadeh, Manouchehr
    Vattenfall Research & Development, Stockholm.
    Fridh, Katja
    Lund University, Lund, Sweden.
    Observations and investigations of frost damage mechanisms of concrete dams in Sweden2013Conference paper (Refereed)
    Abstract [en]

    The major part of the Swedish hydro power development took place between 1945 and1975. At that point of time, significant progress had been made regarding the use of highquality concrete for hydraulic structures. In spite of the progress made, deterioration ofconcrete due to freezing and thawing is still frequent. Superficial damage at the waterlineand spalling of concrete far below the water level on the upstream face of concrete damshave been observed. Knowledge about the deterioration processes is important in order toimprove the efficiency of maintenance of hydro power plants. Results obtained from twoexperimental studies of frost damage mechanisms are presented in this paper.

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  • 47.
    Sjölander, Andreas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. Vattenfall R&D Laboratories.
    Data from structural testing of sprayed and cast shotcrete reinforced with fibres of steel, basalt and synthetic material2022Data set
    Abstract [en]

    In this dataset, data from experimental testing of fibre-reinforced shotcrete is presented. The dataset contains five different fibres made of steel (Dramix 3D, Dramix 4D and Dramix5D), synthetic (BarChip R54) and basalt (MiniBar). Preparation of specimens and testing were performed by Vattenfall R&D in Älvkarleby, Sweden. This first version of the dataset contains the results for shotcrete specimens prepared through casting. The same shotcrete mix was used for all specimens, and three different dosages were used for each of the fibres except for Dramix 5D, for which only two dosages were tested. The dataset contains the shotcrete mix and standard output for the test of compressive strength according to EN 12390-3, residual flexural strength according to EN 14488-3 and energy absorption according to ASTM C1550. This dataset can be used to study how the structural toughness of fibre-reinforced shotcrete is affected by the dosage of fibre. Moreover, the data can be used to compare the structural performance of fibres of different materials. The data also provide a foundation to select a reasonable dosage of fibres to fulfil the structural requirements put on shotcrete in the design phase.

  • 48.
    Sjölander, Andreas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. Vattenfall R&D Laboratories.
    Effective use of fibres of various types and material for shotcrete in rock support for tunnels.2023In: ITA‐AITES World Tunnel Congress / [ed] Georgios Anagnostou, Andreas Benardos, Vassilis P. Marinos, London: Taylor & Francis Group, 2023Conference paper (Refereed)
    Abstract [en]

    Large volumes of steel fibre reinforced shotcrete (sprayed concrete) and steel bolts are commonly used to support tunnels in hard rock. This generates a high CO2-footprint which must be reduced in order to decelerate the continuously increasing average temperature worldwide caused by the emissions of greenhouse gases. Thus, alternative design methods and the possibility to use other materials than steel are currently investigated. Work is ongoing on testing the load-bearing capacity of shotcrete reinforced with fibres of steel, basalt and synthetic materials. This also includes a comparison between tests using Round Determinate Panels (RDP) and four-point bending of beams. Moreover, the practical use of RDP testing as a quality control methodology is also investigated in situ. Here, the goal is to identify several shotcrete mixes suitable for use in tunnelling so that the right material and fibre volume can be used in the right place.

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  • 49.
    Sjölander, Andreas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Effective use of fibres of various types and material for shotcrete in rock support for tunnels2023In: Expanding Underground - Knowledge and Passion to Make a Positive Impact on the World- Proceedings of the ITA-AITES World Tunnel Congress, WTC 2023, Informa UK Limited , 2023, p. 932-939Conference paper (Refereed)
    Abstract [en]

    Large volumes of steel fibre reinforced shotcrete (sprayed concrete) and steel bolts are commonly used to support tunnels in hard rock. This generates a high CO2-footprint which must be reduced in order to decelerate the continuously increasing average temperature worldwide caused by the emissions of greenhouse gases. Thus, alternative design methods and the possibility to use other materials than steel are currently investigated. Work is ongoing on testing the load-bearing capacity of shotcrete reinforced with fibres of steel, basalt and synthetic materials. This also includes a comparison between tests using Round Determinate Panels (RDP) and four-point bending of beams. Moreover, the practical use of RDP testing as a quality control methodology is also investigated in situ. Here, the goal is to identify several shotcrete mixes suitable for use in tunnelling so that the right material and fibre volume can be used in the right place.

  • 50.
    Sjölander, Andreas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    On the Design of Permanent Rock Support Using Fibre-Reinforced Shotcrete2023In: Fibers, E-ISSN 2079-6439, Vol. 11, no 2, p. 20-Article in journal (Refereed)
    Abstract [en]

    Fibre-reinforced shotcrete (sprayed concrete) is one of the major components in the support system for tunnels in hard rock. Several empirical design methodologies have been developed over the years due to the complexity and many uncertainties involved in rock support design. Therefore, this paper aims to highlight how the choice of design methodology and fibre type impacts the structural capacity of the lining and the emission of greenhouse gases (GHG). The paper starts with a review of different design methods. Then, an experimental campaign is presented in which the structural performance of shotcrete reinforced with various dosages of fibres made of steel, synthetic and basalt was compared. A case study is presented in which the permanent rock support is designed based on the presented design methods. Here, only the structural requirements were considered, and suitable dosages of fibres were selected based on the experimental results. The emission of GHG was calculated for all design options based on environmental product declarations for each fibre type. The result in this paper indicates that synthetic fibres have the greatest potential to lower the emissions of GHG in the design phase. Moreover, the choice of design method has a significant impact on the required dosage of fibres.

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