Optimization and Engineering Validation of Flexible Cushion Thickness for Underwater Energy-relief Blasting

To address the challenge of controlling bedrock damage in deep-water blasting operations, this investigation utilized the Xihoumen Road-rail Bridge′s deep-water foundation blasting project as a case study. The research employed a multi-interface wave-impedance model for energy-relief charge structures, combining scaled laboratory experiments with numerical simulations. This study systematically examined the mechanism by which flexible cushion thickness affects bedrock damage at borehole bottoms during underwater energy-relief blasting operations, quantitatively analyzing the evolutionary laws of fracture characteristics, damage radius, and penetration depth across different cushion-thickness configurations. The results demonstrate that the energy-relief structure significantly attenuates shock-wave intensity at the borehole bottom, transforming the damage from localized, concentrated failure to a dispersed fracture distribution. Both the damage radius and penetration depth decrease, then stabilize as the thickness of the flexible buffer layer increases. With a 20 cm buffer thickness, the damage radius measures 27 cm, representing a 48% reduction compared to a conventional charge structure. Based on a comprehensive evaluation of damage mitigation and foundation specifications, 40 cm is determined as the optimal buffer thickness. Field applications confirm that this 40 cm flexible buffer effectively regulates bedrock damage and surface roughness while satisfying the precision requirements for deep-water foundation construction. These findings establish a scientific framework for bedrock damage control in deep-water drilling and blasting operations.