Dynamic behaviors of RC caisson subjected to underwater explosions

Due to the vulnerability of wharves against accidental attacks, the reinforced concrete (RC) caisson quay wall, as a widely adopted wharf form, is faced with the potential threat of underwater explosions. The present work aims to study the dynamic responses and damage modes of caisson against underwater explosions through the underwater explosion test and numerical simulations. Firstly, four shots of underwater explosion test were conducted, including two cases for different focuses, i.e., two shots of the free field underwater explosion with a charge weight of 0.2 and 1 kg respectively, and another two shots of a 1/5 reduced scale caisson specimen subjected to the underwater explosion with a charge weight of 0.2 and 1 kg successively. The underwater explosion overpressure-time histories and periods of bubble pulsation, as well as the deflection-time histories and damage modes of caisson specimen were experimentally obtained. Then, the refined finite element (FE) models were established, including the 1D model for explosion loading and the 3D model for predicting the dynamic behaviors of caisson with adopting the Coupled-Eulerian-Lagrangian algorithms and remapping technology, which were validated by comparing with the test data. Finally, the influences of explosion conditions, such as explosion standoff, depth of burst, and charge weight on the dynamic behaviors of caisson specimens were numerically discussed. It derives that, the existing calculation formulas of overpressure and period of bubble obtained from the spherical charge are also applicable to the group charge; the reflection coefficient of hydraulic RC structure is around 1.7; the bubble pulsation induced by the underwater explosion could further deteriorate the damage level of RC caisson when the blast wave has already led to an inelastic structural response. The present work could provide beneficial references for the blast-resistance evaluation and design of hydraulic RC structures against underwater explosions.