Automated performance monitoring of concrete dams

Sammanfattning: The Swedish hydropower industry operates a large number of power plants and dams geographically spread over the country. The level of safety of a specific dam is to a large extent determined during the design and construction phases that in the case of Swedish hydropower plants took place several decades ago. Condition monitoring of concrete dams, or hydropower concrete structures, has until recently been an area of relatively low priority. Nevertheless, these structures represent a significant economical value. From a dam safety perspective, the reasons for condition monitoring are not significant. But as high availability has high priority, condition monitoring should be considered as one of the tools to use for assuring this. The objectives of the research carried out within the scope of this Ph.D. thesis have been to adapt and develop cost-effective methods and methodology for the automated performance monitoring of concrete dams and their foundations, with specific attention paid to prioritised damage types. The objective has also been to build new knowledge regarding sensor technology. By doing this, the thesis contributes to improving current praxis for the condition monitoring of concrete structures. The thesis covers a series of tasks that are central to condition monitoring: - The introductory chapter of this thesis is devoted to the set automated performance monitoring of hydropower concrete structures in context: The operation and maintenance of hydropower infrastructure are outlined. Statistics about the dam population are given, together with an outline of the main types of ageing processes and an international outlook on concrete dam condition monitoring. Included is also a condensed state-of-the-art review of instrumentation. An outline is given of how the information gained can be used as part of the technical management of hydropower concrete structures. - The methods-chapter includes the choice of deterioration mechanisms and the methods for monitoring the progress of damage. Each method is described, together with identified requirements for development. - The results-chapter builds upon five technical papers. The results achieved in developing the chosen technologies to the state that they can be applied to real structures in the field are summarised. Results from tests in both the laboratory and in the field are presented. - The discussion and conclusions chapter discuss the results versus the goals, and concludes the improved knowledge established. The barriers to employment are discussed, and the drawings of conclusions about how the results can be used to assist improved decision support regarding maintenance measures are made. Finally, there is a discussion about future improvements. Based on three country reviews of the status of concrete dams, three prioritised damage mechanisms have been identified to be followed up by condition monitoring: crack growth, uplift pressure, and dam-crest deformation. Research has been directed to technology options that have proven records in other applications. Based on the state-of-the-art review, three methods were chosen for further development: Time-domain reflectometry (TDR), Digital imaging together with Image processing, and GPS. An assessment of costs shows that the most cost-effective method is digital imaging and image processing, while the most expensive method is GPS. In total, four condition-monitoring investigations have been demonstrated. These include (i) uplift pressure and (ii) dam crest investigations of the Storfallsdammen in River Dalälven, and crack growth/deformation investigations of (iii) draft tube wall of a hydropower plant (Porjus) and (iv) a commuter bridge (Alvik). In cooperation with other research projects, it has been shown that reliability-based stability safety analysis is a good tool for assessing existing concrete dams. Overall, the work contained in this research contributes to improving the knowledge base on how owners of hydropower concrete structures can incorporate condition monitoring into their regular maintenance work. As a result of the research project, it is judged that the introduction of new tools for the maintenance work practised within the Swedish hydropower industry may be possible with, once installed, only a minor increase in the workload of the maintenance organisations.