AbstractThe stability of concrete dams is commonly evaluated in terms of sliding, overturning, and bearing capacity. Although these failure modes are simple to evaluate analytically, they may not accurately reflect a dam’s actual failure behavior because of inherent idealizations and assumptions. Previous studies have shown that the failure mechanism for dams often involves both sliding and overturning, particularly in dams with uneven rock-concrete interfaces and large-scale asperities. This article presents results from 1:5 scale model tests of a buttress dam, conducted to investigate the behavior and failure mechanism of dams featuring large-scale asperities in the rock-concrete interface. Each of the twelve scale models incorporated a specific combination of interface geometry, rock bolts, reinforcement, and rock joints. The results were compared with FEA and analytical estimates for sliding, overturning, and combined sliding and overturning failure. The scale models failed through a combination of sliding and overturning, with significant strain concentrations observed at the asperities’ upstream faces and the toe at peak load, indicating reliance on these regions for force transfer. The presence of rock bolts and a rock joint altered the load capacity but generally did not affect the overall failure mechanism. The results indicate that dams with irregular interfaces may exhibit significant overstrength compared to current assessment practices in dam safety guidelines.