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  • Sundell, Jonas, et al. (författare)
  • Comprehensive risk assessment of groundwater drawdown induced subsidence
  • 2019
  • Ingår i: Riskhantering vid grundvattensänkning i sättningskänsliga områden: Kostnads-nyttoanalys av säkerhetshöjande åtgärder i infrastrukturprojekt.
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a method for risk assessment of groundwater drawdown induced land subsidence when planning for sub-surface infrastructure. Since groundwater drawdown and related subsidence can occur at large distances from the points of inflow, the large spatial extent often implies heterogeneous geological conditions that cannot be described in complete detail. This calls for estimation of uncertainties in all components of the cause-effect chain with probabilistic methods. In this study, we couple four probabilistic methods into a comprehensive model for economic risk quantification: a geostatistical soil-stratification model, an inverse calibrated groundwater model, an elasto-plastic subsidence model, and a model describing the resulting damages and costs on individual buildings and constructions. Groundwater head measurements, hydraulic tests, statistical analyses of stratification and soil properties and an inventory of buildings are inputs to the models. In the coupled method, different design alternatives for risk reduction measures are evaluated. Integration of probabilities and damage costs result in an economic risk estimate for each alternative. Compared with the risk for a reference alternative, the best prior alternative is identified as the alternative with the highest expected net benefit. The results include spatial probabilistic risk estimates for each alternative where areas with significant risk are distinguished from low-risk areas. The efficiency and usefulness of this modelling approach as a tool for communication to stakeholders, decision support for prioritization of risk reducing measures, and identification of the need for further investigations and monitoring are demonstrated with a case study of a planned railway tunnel in Varberg, Sweden.
  • Acuña, José, 1982- (författare)
  • Distributed thermal response tests New insights on U-pipe and Coaxial heat exchangers in groundwater-filled boreholes
  • 2013
  • Ingår i: EFFSYS. - Stockholm : KTH Royal Institute of Technology. - 978-91-7501-626-9
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • <p>U-pipe Borehole Heat Exchangers (BHE) are widely used today in ground source heating and cooling systems in spite of their less than optimal performance. This thesis provides a better understanding on the function of U-pipe BHEs and Investigates alternative methods to reduce the temperature difference between the circulating fluid and the borehole wall, including one thermosyphon and three different types of coaxial BHEs.</p><p>Field tests are performed using distributed temperature measurements along U-pipe and coaxial heat exchangers installed in groundwater filled boreholes. The measurements are carried out during heat injection thermal response tests and during short heat extraction periods using heat pumps. Temperatures are measured inside the secondary fluid path, in the groundwater, and at the borehole wall. These type of temperature measurements were until now missing.</p><p>A new method for testing borehole heat exchangers, Distributed Thermal Response Test (DTRT), has been proposed and demonstrated in U-pipe, pipe-in-pipe, and multi-pipe BHE designs. The method allows the quantification of the BHE performance at a local level.</p><p>The operation of a U-pipe thermosyphon BHE consisting of an insulated down-comer and a larger riser pipe using CO<sub>2</sub> as a secondary fluid has been demonstrated in a groundwater filled borehole, 70 m deep. It was found that the CO<sub>2 </sub>may be sub-cooled at the bottom and that it flows upwards through the riser in liquid state until about 30 m depth, where it starts to evaporate.</p><p>Various power levels and different volumetric flow rates have been imposed to the tested BHEs and used to calculate local ground thermal conductivities and thermal resistances. The local ground thermal conductivities, preferably evaluated at thermal recovery conditions during DTRTs, were found to vary with depth. Local and effective borehole thermal resistances in most heat exchangers have been calculated, and their differences have been discussed in an effort to suggest better methods for interpretation of data from field tests.</p><p>Large thermal shunt flow between down- and up-going flow channels was identified in all heat exchanger types, particularly at low volumetric flow rates, except in a multi-pipe BHE having an insulated central pipe where the thermal contact between down- and up-coming fluid was almost eliminated.</p><p>At relatively high volumetric flow rates, U-pipe BHEs show a nearly even distribution of the heat transfer between the ground and the secondary fluid along the depth. The same applies to all coaxial BHEs as long as the flow travels downwards through the central pipe. In the opposite flow direction, an uneven power distribution was measured in multi-chamber and multi-pipe BHEs.</p><p>Pipe-in-pipe and multi-pipe coaxial heat exchangers show significantly lower local borehole resistances than U-pipes, ranging in average between 0.015 and 0.040 Km/W. These heat exchangers can significantly decrease the temperature difference between the secondary fluid and the ground and may allow the use of plain water as secondary fluid, an alternative to typical antifreeze aqueous solutions. The latter was demonstrated in a pipe-in-pipe BHE having an effective resistance of about 0.030 Km/W.</p><p>Forced convection in the groundwater achieved by injecting nitrogen bubbles was found to reduce the local thermal resistance in U-pipe BHEs by about 30% during heat injection conditions. The temperatures inside the groundwater are homogenized while injecting the N<sub>2</sub>, and no radial temperature gradients are then identified. The fluid to groundwater thermal resistance during forced convection was measured to be 0.036 Km/W. This resistance varied between this value and 0.072 Km/W during natural convection conditions in the groundwater, being highest during heat pump operation at temperatures close to the water density maximum.</p>
  • Norrman, Jenny, 1971-, et al. (författare)
  • Integration of the subsurface and the surface sectors for a more holistic approach for sustainable redevelopment of urban brownfields
  • 2016
  • Ingår i: Science of the Total Environment. - 0048-9697. ; 563, s. 879-889
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents a holistic approach to sustainable urban brownfield redevelopment where specific focus is put on the integration of a multitude of subsurface qualities in the early phases of the urban redevelopment pro- cess, i.e. in the initiative and plan phases. Achieving sustainability in brownfield redevelopment projects may be constrained by a failure of engagement between two key expert constituencies: urban planners/designers and subsurface engineers, leading to missed opportunities and unintended outcomes in the plan realisation phase. A more integrated approach delivers greater benefits. Three case studies in the Netherlands, Belgium and Sweden were used to test different sustainability assessment instruments in terms of the possibility for knowl- edge exchange between the subsurface and the surface sectors and in terms of cooperative learning among experts and stakeholders. Based on the lessons learned from the case studies, a generic decision process frame- work is suggested that supports holistic decision making. The suggested framework focuses on stakeholder involvement, communication, knowledge exchange and learning and provides an inventory of instruments that can support these processes.
  • Karlsson, Mats, 1974-, et al. (författare)
  • Consequences of sample disturbance when predicting long-term settlements in soft clay
  • 2016
  • Ingår i: Canadian Geotechnical Journal. - 1208-6010 .- 0008-3674. ; 53:12, s. 1965-1977
  • Tidskriftsartikel (refereegranskat)abstract
    • An approach for assessing the effects of sample quality is presented. Soil samples were taken using a 50 mm Swedish STII piston sampler and the Norwegian University of Science and Technology (NTNU) mini-block sampler from a soft clay test site. Differences in laboratory test results are identified for several stress paths, assisted by simulations made using an advanced constitutive model. Hitherto such comparisons have focused on differences in basic engineering properties such as strength and stiffness. The effect of choosing alternative model parameters from piston and block samples is demonstrated through the analysis of the long-term settlement of an embankment. The simulations show that substantially larger settlements and lateral displacements are predicted using parameters obtained from the piston samples. Furthermore, the magnitude of the differences is larger than expected. This demonstrates that for this application, relatively small differences in the assessed sample quality, using traditional laboratory data interpretation methods, are amplified when applied to a prototype boundary value problem. It is suggested that a little more care in sampling and testing can result in large cost savings as a result of the more reliable model parameters that can be extracted, particularly when the improved sampling is combined with the use of an advanced constitutive model.
  • Mathern, Alexandre, 1986-, et al. (författare)
  • Experimental study of time-dependent properties of a low-pH concrete for deposition tunnels
  • 2018
  • Ingår i: Proceedings of the International Federation for Structural Concrete 5th International fib Congress, 7–11 October 2018, Melbourne, Australia.
  • Konferensbidrag (refereegranskat)abstract
    • The Swedish Nuclear Fuel and Waste Management Company developed a method for the final disposal of canisters for spent nuclear fuel in tunnels at depths of about 500 meters. The concept for closure of the deposition tunnels is based on a bentonite seal supported by a spherical concrete dome structure. In order to fulfil the requirements specific to the repository concept, a special mix of low-pH self-compacting concrete was developed. A series of large-scale castings and laboratory tests were conducted to gain experience on this low-pH concrete mix, in conjunction with the full-scale demonstration test of an unreinforced concrete dome plug in the underground hard rock laboratory in Äspö, Sweden. The laboratory tests aimed at studying the creep properties under high sustained compressive stresses of the low-pH concrete mix, its shrinkage properties and the properties of the rock-concrete interface. This paper provides an overview of these tests and analyses the latest results of the recently completed creep tests, which include 6 years of measurements. These results allow to improve understanding of the structural behaviour of the concrete plug and to assess the effects of the very high pressure acting on the plug on its deformations, cracking and water tightness.
  • Persson, Peter, et al. (författare)
  • Effect of structural design on traffic-induced building vibrations
  • 2017
  • Ingår i: Procedia Engineering. - Elsevier. - 1877-7058. ; 199, s. 2711-2716
  • Tidskriftsartikel (refereegranskat)abstract
    • Population growth and urbanization results in densified cities, where new buildings are being built closer to existing vibration sources, and new transportation systems are constructed closer to existing buildings. Potential disturbing vibrations are one issue to consider in planning urban environments and densification of cities. Vibrations can be annoying for humans but also for sensitive equipment in, for example, hospitals. In determining the risk for disturbing vibrations, the distance between the source and the receiver, the ground properties, and type and size of the building are governing factors. In the paper, a study is presented aiming at investigating the influence of various parameters of the building’s structural design on vibration levels in the structure caused by ground surface loads, e.g. traffic. Parameters studied are related to the type of construction material (if it would be a light or heavy structure), and to the slab thickness. The study is limited to the structural response at frequencies near the first resonance frequency of the soil. The finite element method is employed for discretizing the building structure that is coupled to a semi-analytical model considering a layered ground.
  • Merisalu, Johanna, 1990-, et al. (författare)
  • Hydrogeological reference conditions for assessment of environmental impact and for grouting design
  • 2018
  • Ingår i: ISRM International Symposium - 10th Asian Rock Mechanics Symposium, ARMS 2018.
  • Konferensbidrag (refereegranskat)abstract
    • Dewatering of groundwater resources induced by leakage into underground constructions can cause land subsidence, damage to constructions and their foundations and disturbances of groundwater dependent ecosystems. To reduce the environmental impacts, safety measures, e.g. sealing fractures by grouting to reduce inflow of groundwater or artificial recharge to maintain groundwater levels, must be implemented. Site investigations of the total geological and hydrogeological conditions at a site before construction is, due to financial aspects, most often not possible. To handle these uncertainties in the design- and construction process, it is suitable to use the observational method, which include the idea of identification, confirmation or rejection, and revision of the most probable and unfavorable conditions, and predefined technical design solutions for conditions that can reasonable be anticipated or foreseen. To assess the geological and hydrogeological conditions at an early stage of a project we suggest that geological and related hydrogeological reference conditions are used. Fundamental to our approach using reference conditions is the grouping of materials with similar geological and hydrogeological conditions and engineering characteristics. In this paper, we present conceptualizations of five reference conditions common in western Sweden and two examples of reference conditions in Singapore. The conceptualization of reference conditions includes a description of: the geological material; the hydrogeological properties and behavior within the environment; and the engineering characteristics related to water control and grouting. Examples of technical design solutions used to adopt to project specific requirements for inflow and drawdown for underground constructions constructed in environments representing one of the suggested reference conditions in western Sweden are also presented to exemplify the application of reference conditions for technical design.
  • Olsson, Lars (författare)
  • Rain resistance of façades with façade details: A summary of three field and laboratory studies
  • 2018
  • Ingår i: Journal of Building Physics. - 1744-2591. ; 41:6, s. 521-532
  • Tidskriftsartikel (refereegranskat)abstract
    • One of the main functions of the exterior walls and façades is to protect the indoor and the sensitive parts of construction from the outdoor climate. Exposure of driving rain is the most prominent moisture source a wall has to resist. Despite this, there is a lack of information on rain resistance. Field measurements on real-life external walls show that recurrent water leakage under driving rain conditions is observed in five out of seven new-built houses in Sweden, including those with ventilated façades. About a 100 commercial laboratory façade tests, mounted by façade suppliers, and targeted laboratory experiments showed that it is almost impossible to achieve fully tight façade solutions, and keep them sealed. Nearly, all test walls with façade details leaked, almost regardless of façade type and sealing efforts. The results from field and laboratory measurements of rain resistance in new buildings in Sweden show that façades are usually not water-tight and also that very small deficiencies can cause substantial amount of water leakage.
  • Persson, Peter (författare)
  • Vibrations in a Built Environment : Prediction and Reduction
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Vibrations in a built environment can exceed the requirements for sensitive equipment in a building or can cause annoyance to residents. Hence, there is often a need for reducing such vibrations. The vibrations can originate from ambient sources such as motorway traffic, or from internal sources such as people walking inside the building. Disturbing vibrations can be reduced by reduction measures. Vibration-reduction measures can be evaluated numerically, with for instance the finite element method, to avoid construction of expensive mock-ups. In the thesis, large finite element models involving several physical domains (e.g. road, soil, bedrock, and building parts) were developed to study the effect of vibration-reduction measures.Ground vibrations can be reduced by installing a wave barrier between an external source and a receiver. As concluded in the thesis, an empty barrier (i.e. a trench) installed in the soil has the ability to reduce the ground-vibration level by approximately 60%. If the barrier contains a solid material, however, the level of reduction is reduced to approximately 30%. At long distances, at around 500 m and longer, from the vibration source, an amplification in vibration is observed. At such distances, moreover, the ground motion follows the motion of the bedrock. Another example of a wave obstacle that is studied in the thesis involves shaping the landscape surrounding a building. The topsoil that is usually transported from the construction site can be used to construct hills and valleys that constitute the shaped landscape. However, this can result in anything from an appreciable reduction to an appreciable amplification in the ground-vibration levels, depending on how the landscape is formed. If constructed properly, the reduction in the level of vibration can reach approximately 35%. Vibrations from both external and internal sources can be reduced by modifying the properties of the concrete slabs and the soil underneath. The soil properties can be improved by mixing the soil with a binder, in order to stiffen the soil. Is is shown in the thesis that by using stabilised soil underneath a concrete slab, vibrations originating from motorway traffic can be reduced by almost 60%, and up to 80% for an internal pedestrian load. By using a time-efficient numerical model developed in the thesis, the effect by using different positions for the supports of a water-pipe system on vibrations transmitted to other parts of buildings was studied. Because frequency peaks can be avoided, a marked change of vibration characteristics can be achieved. A reduction of more than 60% in the transmitted vibrations was observed. The general methods and measures presented in the thesis are exemplified by the conceptual design process of the MAX IV Laboratory, a vibration-sensitive research facility. This laboratory exhibited the phenomena needed for selecting it as a comprehensive example case.
  • Proceedings of the 14<sup>th</sup> ICOLD International Benchmark Workshop on Numerical Analysis of Dams
  • 2017
  • Proceedings (redaktörskap) (refereegranskat)abstract
    • <p>Every second year, the Technical Committee A (Computational Aspects of Dam Analysis and Design) of ICOLD organizes an international benchmark workshop on numerical analysis of dams. The purpose is to share knowledge and experience regarding numerical modelling within the fields of dam safety, planning, design, construction as well as operation and maintenance of dams. The Terms of Reference for Committee A state; ”BenchmarkWorkshops are organised to compare numerical models between one another and/or with reference solutions, including the dissemination and publication of results”.</p><p> The 14<sup>th</sup> ICOLD International Benchmark Workshop on Numerical Analysis of Dams was held from the 6<sup>th</sup> to the 8<sup>th</sup> September 2017 in Stockholm, the capital of Sweden. It was organized by the Local Organizing Committee, on behalf of the Swedish National Committee of ICOLD (SwedCold) and the ICOLD Technical Committee A. It was hosted by KTH Royal Institute of Technology, Sweden’s largest technical research and learning institution and one of Europe’s leading technical universities. With respect to hydropower and dam engineering, KTH has for many years been active within of the Swedish hydropower Center (SVC), a key centre for research and educational activities in Sweden. SwedCOLD established in 1931, and is one of the oldest members of the International Commission On Large Dams, ICOLD. The development of hydro power for electricity production was initiated in the late 19th century and made the large scale industrialisation in Sweden possible. About 2000 hydropower plants are in operation in Sweden today, producing almost half of the total electricity supply. Considering the many and relatively old dams in Sweden, organizing the benchmark workshop was important to increase the knowledge regarding managing aging hydropower structures.</p><p>The 14<sup>th</sup> ICOLD International Benchmark Workshop has addressed current challenges regarding design and maintenance of existing dams and improved the understanding of these by exchange of experience on the use of numerical modelling for design, performance evaluation and safety assessment of dams. On behalf of the organizing committee, I would like to express my sincere appreciation to the formulators/moderators of each theme for their outstanding work to prepare the themes, reviewing the papers and evaluating the results. I also want to thank all participants to the benchmark workshop for their contributions and their presence to this benchmark workshop. Finally, the support from the Technical Committee A and the support from the companies and organizations that sponsored this benchmark workshop is gratefully acknowledged.</p>
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