Toward Realistic Failure Evaluations for Concrete Buttress Dams

Abstract: 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.