Influence of concrete material models on gravity dam subjected to under water explosion

Concrete gravity dams are critical infrastructures, and their structural safety under underwater explosion (UndEx) loading is a major concern. This study investigates the dynamic response of the Koyna Dam under UndEx using two non-linear concrete material models: the concrete damage plasticity (CDP) model and the Johnson–Holmquist 2 (JH-2) model. A fully coupled 3D dam–reservoir interaction is simulated using the coupled acoustic–structural approach to capture shock wave propagation and structural response. The effects of trinitrotoluene weight, detonation depth and standoff distance on dam behaviour are systematically examined. Results show that the JH-2 model captures high-strain-rate effects and fragmentation more effectively, while the CDP model predicts more gradual damage evolution with higher energy dissipation. The comparison highlights significant differences in predicted stress distribution, displacement response and damage patterns, emphasising the importance of selecting an appropriate material model for blast-resistant design of gravity dams.