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.

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.

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.

Concrete dams, complex structures supporting massive loads, have traditionally been assessed using simplified 2D analytical stability analyses based on the rigid body assumption. Previous studies have shown that 3D behavior, such as the interaction between the monoliths and the valley's geology, can greatly impact the load-bearing capacity of gravity dams but remains largely unexplored in buttress dams. Internal failure modes have also been shown to impact the load-bearing capacity and failure modes of concrete dams. 

The dam breach geometry and breach development time are important factors for flooding simulations used for emergency plans. There are no available methods for estimating the breach parameters for concrete dams. Instead, they are usually assumed based on simplified national recommendations, which introduces large uncertainties in the analysis. Thus, developing methods to estimate failure behavior in concrete gravity and buttress dams could significantly enhance flood simulation accuracy.

This licentiate thesis aims to develop more realistic analysis methods for determining the load-bearing capacity and failure behavior of concrete buttress dams. To achieve this aim, studies using physical model tests were conducted to determine the 3D effects of the boundary conditions and the interaction between the monoliths and verify the results from finite element simulations. Numerical studies were performed to examine the failure behavior of concrete buttress dams and to determine suitable methods for such simulations. 

The results from the physical model tests suggest that 3D effects significantly impact the load-bearing capacity and the failure behavior of concrete buttress dams. Therefore, the entire dam should be considered in stability analyses rather than just single monoliths. The numerical studies showed that finite element models could successfully simulate dam failures, including the 3D behavior of concrete buttress dams and internal failure modes. However, there remain questions about the best methods for representing phenomena such as first-order roughness, valley shape, and fracture planes in these models.

The model tests showed that while dam failures can occur abruptly with little to no initial signs of displacement, the presence of rough foundations, cohesion, and rock-strengthening measures in real-world dams suggests actual dam failures may not be as sudden. The results helped establish knowledge in the field to potentially create better alarm limits for automatic monitoring systems. 

Betongdammar är komplexa konstruktioner som bär stora laster, men traditionellt har de utvärderats med förenklade analytiska stabilitetsanalyser i 2D baserat på stelkroppsantagandet. Tidigare studier har visat att 3D-beteende, såsom interaktionen mellan monoliterna och älvdalens topologi, kan ha en betydande inverkan på lastkapaciteten hos gravitationsdammar men är i stort sett outforskat i lamelldammar. Interna brottmoder har också visats påverka bärförmågan och brottmoderna hos betongdammar.

Bräschens form och utvecklingstiden för dammbrott är viktiga faktorer för översvämningssimuleringar som används i beredskapsplanering och riskanalyser. Ingen metod finns för att uppskatta dessa parametrar för betongdammar. Istället utgår analysen från förenklade antaganden, vilka introducerar stor osäkerhet i analysen. Därmed skulle utveckling av metoder för att uppskatta brottbeteende för gravitations- och lamelldammar kunna förbättra tillförlitligheten i översvämnings-simuleringar avsevärt.

Denna licentiatuppsats, som involverar studier med fysiska modellförsök och finita element-simuleringar, syftar till att utveckla mer realistiska analysmetoder för att bestämma bärförmågan och brottbeteendet hos lamelldammar. De fysiska modellförsöken genomfördes för att bestämma 3D-effekterna av randvillkor och interaktionen mellan monoliterna och verifiera resultaten från finita element-simuleringar. Numeriska studier genomfördes för att undersöka brottbeteendet hos lamelldammar och för att bestämma lämpliga metoder för sådana simuleringar.

Resultaten från modellförsöken visade att 3D-effekter avsevärt påverkar lastkapaciteten och brottbeteendet hos lamelldammar, vilket indikerar att hela dammen bör beaktas i stabilitetsanalyser. Numeriska studier visade att finita element-modeller framgångsrikt kunde simulera dammbrott, inklusive 3D-beteendet. Dock återstår frågor om de mest effektiva metoderna för att representera fenomen som ojämn grundläggning och älvdalens topologi.

Modellförsöken visade att dammbrott kan inträffa abrupt, med liten eller ingen initial förskjutning. Dock tyder närvaron av ojämn grundläggning, kohesion och förstärkningsåtgärder i berget i verkliga dammar på att faktiska dammbrott inte är lika plötsliga som observerat i modelltesterna. Resultaten har bidragit till att utveckla kunskap inom området och kan potentiellt leda till förbättrade metoder för att fastställa larmgränser för automatiska övervakningssystem.

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.

Many of the world’s concrete dams are approaching the end of their expected service life and many of these dams are cracked due to environmental effects. It is thus desirable to be able to extend the service life of many of these dams. It is therefore important to develop reliable methods of analysis to assess the current status of these dams and to determine the safety of these, partly damaged structures. A slender reinforced concrete arch dam is used as a case study with the aim of predicting the structural response, the cracks found in-situ and of assessing the safety of the dam. This dam has cracked extensively along the downstream face primarily due to seasonal temperature variations. A detailed finite element model has been developed to simulate the history of the dam with the variations in ambient conditions that have occurred over its lifetime. The results show good agreement regarding both the crack pattern and displacement of the dam. A procedure to simulate a progressive dam failure, starting from the current state, is utilized to assess the current level of safety. The results show that the cracking has a limited effect on the safety factor of the dam. 

Dam failures are catastrophic events and in order to improve safety, engineers must have good tools for analysis and an understanding of the failure process. Since there are few cases of real failures in concrete dams, which can work as validation, physical model tests are a good way of improving numerical models and the understanding of the failure process. In this article, a physical model test of the buttress from a concrete Ambursen type dam is used as a benchmark for calibrating a FE-model. The dam failure is thereafter simulated using the concept of safety commonly used in the design codes. The advantages and drawbacks of performing load- and displacement-controlled simulations are compared. A new method for performing displacement-controlled simulations, using nonlinear springs to introduce the hydrostatic pressure and ice load is thereafter suggested and tested. The proposed method gives results which corresponds to the classical methods of analysis but has some advantages. Primarily, the new method is stable and does not suffer from convergence issues as was the case with the other methods. It is also simple to introduce in most commercial software compared to classical displacement-controlled simulations.

Dams located in cold areas are subjected to large seasonal temperature variations and many concrete dams have cracked as a result. In the 14th International Commission on Large Dams (ICOLD) Benchmark Workshop, a case study was presented where contributors should predict the cracking and displacements due to seasonal variations. In this paper, the conclusions from this case study are presented. Overall, the results from the contributors are well in line with the observations that can be made on the dam and the measurements performed. This shows that using non-linear numerical models is a suitable tool to accurately predict cracking and estimate the displacements of cracked dams. This case study also highlighted important aspects that need special consideration in order to obtain realistic results that can be used to predict the crack pattern, these being: (1) the importance of performing transient thermal analyses based on robin boundary conditions; (2) the influence of contact formulation between the concrete dam and the foundation; and (3) the use of realistic non-linear material properties. The results and conclusions presented in this paper constitute one important step in achieving best practices to estimate dam safety and better understand the potential failure modes and ageing of concrete dams.