Papers by Christian Bernstone
Measurement, Jul 1, 2009
A digital image analysis technique for crack monitoring using a standard web-camera has been furt... more A digital image analysis technique for crack monitoring using a standard web-camera has been further developed to acquire continuous data sets on crack development in concrete dams. The method is based on an existing robust and straightforward non-contact method for experimental deformation analysis. It allows for the measurement of suspected serious cracks, identified from inspections, through a sequence of images captured at intervals. The crack opening displacements at the surface of investigated objects are obtained by an algorithm that makes it possible to automatically track the motions of discrete markers painted on the object surface markers and compute their centre of mass in a sequence of images. The data acquisition process is straightforward and is well suited for this type of environment. Results from laboratory experiments and a field-test on a commuter bridge in Sweden are presented. The study implies that the technique can be useful for hydropower concrete structure applications.
Elsevier eBooks, 2005
ABSTRACT
AGU Fall Meeting Abstracts, Dec 1, 2020
5th EEGS-ES Meeting, 1999
The Swedish hydropower industry operates a large number of power plants and dams geographically s... more The Swedish hydropower industry operates a large number of power plants and dams geographically spread over the country. The level of safety of a specific dam is to a large extent determined during the design and construction phases that in the case of Swedish hydropower plants took place several decades ago. Condition monitoring of concrete dams, or hydropower concrete structures, has until recently been an area of relatively low priority. Nevertheless, these structures represent a significant economical value. From a dam safety perspective, the reasons for condition monitoring are not significant. But as high availability has high priority, condition monitoring should be considered as one of the tools to use for assuring this. The objectives of the research carried out within the scope of this Ph.D. thesis have been to adapt and develop cost-effective methods and methodology for the automated performance monitoring of concrete dams and their foundations, with specific attention paid to prioritised damage types. The objective has also been to build new knowledge regarding sensor technology. By doing this, the thesis contributes to improving current praxis for the condition monitoring of concrete structures. The thesis covers a series of tasks that are central to condition monitoring: - The introductory chapter of this thesis is devoted to the set automated performance monitoring of hydropower concrete structures in context: The operation and maintenance of hydropower infrastructure are outlined. Statistics about the dam population are given, together with an outline of the main types of ageing processes and an international outlook on concrete dam condition monitoring. Included is also a condensed state-of-the-art review of instrumentation. An outline is given of how the information gained can be used as part of the technical management of hydropower concrete structures. - The methods-chapter includes the choice of deterioration mechanisms and the methods for monitoring the progress of damage. Each method is described, together with identified requirements for development. - The results-chapter builds upon five technical papers. The results achieved in developing the chosen technologies to the state that they can be applied to real structures in the field are summarised. Results from tests in both the laboratory and in the field are presented. - The discussion and conclusions chapter discuss the results versus the goals, and concludes the improved knowledge established. The barriers to employment are discussed, and the drawings of conclusions about how the results can be used to assist improved decision support regarding maintenance measures are made. Finally, there is a discussion about future improvements. Based on three country reviews of the status of concrete dams, three prioritised damage mechanisms have been identified to be followed up by condition monitoring: crack growth, uplift pressure, and dam-crest deformation. Research has been directed to technology options that have proven records in other applications. Based on the state-of-the-art review, three methods were chosen for further development: Time-domain reflectometry (TDR), Digital imaging together with Image processing, and GPS. An assessment of costs shows that the most cost-effective method is digital imaging and image processing, while the most expensive method is GPS. In total, four condition-monitoring investigations have been demonstrated. These include (i) uplift pressure and (ii) dam crest investigations of the Storfallsdammen in River Dalalven, and crack growth/deformation investigations of (iii) draft tube wall of a hydropower plant (Porjus) and (iv) a commuter bridge (Alvik). In cooperation with other research projects, it has been shown that reliability-based stability safety analysis is a good tool for assessing existing concrete dams. Overall, the work contained in this research contributes to improving the knowledge base on how owners of hydropower concrete structures can incorporate condition monitoring into their regular maintenance work. As a result of the research project, it is judged that the introduction of new tools for the maintenance work practised within the Swedish hydropower industry may be possible with, once installed, only a minor increase in the workload of the maintenance organisations.
Geophysical investigations were carried out on two old waste disposal sites, Lernacken and Lackal... more Geophysical investigations were carried out on two old waste disposal sites, Lernacken and Lackalänga, both situated in the province of Scania in southern Sweden. The objectives of the surveys were to map the internal structure and to delineate the extent of deposited waste, as well as to gain information about the local geology. The methods used were 2D DC resistivity, frequency domain electromagnetics (FDEM) and magnetics. The resistivity data sets were interpreted with 2D smoothness constrained inversion, and the FDEM and the magnetic data sets were contoured. The objectives were successfully met, including delineation of sludge ponds, a coastal saltwater front and geological structures, and identification of the positions of buried metal objects. In addition, at Lernacken leakage plumes were identified by the resistivity survey. The slingram EM equipment was rapid, whereas the 2D DC resistivity surveys provided valuable depth information that allowed the construction of quasi 3D models of the ground. The in-phase component in slingram measurements was especially good at localising individual metal objects, but the total field magnetic measurements also worked well.
Energy Procedia, 2013
The present paper concerns the importance of a combined modelling and experimental effort to deve... more The present paper concerns the importance of a combined modelling and experimental effort to develop physicsbased combined thermodynamic and transient flow models for CO 2-transport pipelines. Such models need to handle both multiple components and two-phase flow, which can occur both during normal operation and transient situations, such as first fill and depressurization. Moreover, these models can provide useful input to risk analyses and design of mitigation actions of undesirable incidents like pipeline rupture and well blow-outs. This paper discusses various physical phenomena, design issues and solutions by using the experience from actual cases encountered by Vattenfall, Gassco and Statoil. Among the key issues are the minimum temperature in the pipe wall during depressurization and the magnitude of pressure oscillations during transient operation.
Journal of Environmental and Engineering Geophysics, Jun 1, 1999
Summary One of the most common failures in embankment dams is internal erosion of the body and in... more Summary One of the most common failures in embankment dams is internal erosion of the body and in the foundation. Vattenfall leads a joint research project for assessing the potential of geophysical methods for detecting flaws (with unknown position and size) within the core of an experimental dam in Alvkarleby, Sweden. Equipment for measuring seismic, resistivity and temperature data were installed within the core at different depths and in other areas of the dam. In this study, seismic investigations, such as P-wave reflection seismic and P-wave traveltime tomography, focused on testing and, if possible, detecting the built-in flaws in an early stage before water filling the dam. The reflection seismic results for the top middle and upstream hydrophone lines show high resolution in the first meters of the sections. Repetition of the seismic surveys every two months may improve the identification of the defects and provide a time-lapse seismic study. Synthetic traveltime tomography results indicate the defect position, but fail in recovering its P-wave velocity and size. Acquiring seismic data once the dam reservoir is filled will provide more insights about the potential of this method.
ABSTRACT Two landfills were investigated aiming at finding out what advantages could come out of ... more ABSTRACT Two landfills were investigated aiming at finding out what advantages could come out of using two geophysical methods providing each geometrical information or mechanical information in combination. An old landfill previously characterized by 2D-resistivity ...
Journal of Geotechnical and Geoenvironmental Engineering, 2009
The context of structural monitoring of concrete dams as part of hydropower assets management is ... more The context of structural monitoring of concrete dams as part of hydropower assets management is described. A tool that fits well into this context is the control of the uplift pressure of concrete dams. A monitoring technique suitable for this purpose was ...
A relatively large 2D inverted CVES resistivity data set from a waste pond area in southern Swede... more A relatively large 2D inverted CVES resistivity data set from a waste pond area in southern Sweden was visualized as an animated 3D model using state-of-the-art techniques and tools. The presentation includes a description of the hardware and software used, outline of the case study and examples of scenes from the animation’.
Environmental geology, Jan 18, 2000
Geophysical investigations using 2-D DC resistivity were carried out on old parts of two similar ... more Geophysical investigations using 2-D DC resistivity were carried out on old parts of two similar landfills, with waste of different ages. The data sets, which included high data density in both vertical and horizontal directions, were interpreted with 2-D smoothness constrained inversion. The landfills were excavated after the surveying. The objective was to test the capability of the resistivity method as a pre-characterization technique. The objectives were only partially fulfilled. First, the moisture content was the parameter that appeared to exert the dominant control over the resistivity distribution of the landfill. The most important potential information that can be recovered is, therefore, an indication of the waste piles hydraulics. Second, it was neither possible to estimate the amount of recoverable soils, nor to correlate the type of waste with the resistivity models. However, discrete anomalies were identified, and if specific materials are searched for, the resistivity models indicate possible places to search.
Journal of Applied Geophysics, Aug 1, 2021
Abstract Electrical resistivity tomography has potential as a complementary long-term monitoring ... more Abstract Electrical resistivity tomography has potential as a complementary long-term monitoring method in embankment dams; however, the 3D character of the geometry including the shape of the embankment, its internal zoned construction and the reservoir water make interpretation challenging. To tackle this problem, a qualified inversion model considering the 3D environment is necessary. In this paper, prior information about the resistivity of different parts of a test embankment dam was used as constraints in order to increase the capability of defect detection in a complex 3D context. Five small defects were incorporated into the core of the model. Laboratory measurements were made on samples of the materials intended to be used for the construction of a test embankment dam, and resistivity values provided from the laboratory measurements were used in the forward modelling. A measurement sequence of around 8000 synthetic data points using extended gradient, crossline bipole-bipole and corner arrays between horizontal-horizontal, vertical-vertical, and vertical-horizontal lines were modelled and inverted all at once. The structural constraints were applied to increase the accuracy of inversion, using the L1 and L2 methods. Different mesh qualities with different boundaries for each region and 3D geometric factor calculation were applied for the inversion to evaluate the effects of region control incorporated in the inversion process. The results showed that L1 and L2 norm inversions combined with region control can determine the location of very small defects and finding the defects located near each other, respectively. Removing the region control from the inversion caused unrealistic resistivity prediction for some regions and the inability to discover the dam defects. Therefore, the proposed methodology can decrease non-uniqueness in the inversion and make time-lapse ERT a valuable monitoring tool that complements other instrumentation techniques and based on these results it was concluded promising to continue with the construction of the test dam using the same type of defects and electrode set-up, for verification under field-conditions.
Energy Procedia, Feb 1, 2009
In Denmark, Vattenfall has as decision support investigated different cases to build a CCS demons... more In Denmark, Vattenfall has as decision support investigated different cases to build a CCS demonstration plant. The study described here, looks into possible transportation options related to different CO 2 storage alternatives considered for two studied power plant locations. Based on this study and other decision material, a choice has been made for location and planning of the first CCS demonstration chain in Denmark, including capture, transport and storage. Studied alternative storage locations were: aquifer on the northern shore of the Danish island Sjaelland two hub locations on the Norwegian west coast aquifer offshore the Danish west coast two onshore aquifers at Jutland For these possible storage alternatives, the following transportation options were considered: pipeline onshore pipeline offshore ship, liquefied/refrigerated CO 2 ship, compressed CO 2 barge, liquefied/refrigerated CO 2 barge, compressed CO 2
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Papers by Christian Bernstone