Experimental study on anti-penetration performance of coral reef limestone

Abstract

[Objective] The anti-penetration performance of coral reef limestone is of great significance for underground engineering construction and defensive capacity enhancement on islands and reefs. [Methods] To rapidly evaluate the anti-penetration performance of coral reef limestone and establish a penetration depth calculation formula, coral reef limestone with a sandstone-gravel structure from a specific island reef in the South China Sea was used as the research object. The penetration tests with small-mass arc-shaped pointed kinetic energy projectiles within the velocity range of 500~1 100 m/s were conducted using a self-developed high-velocity impact penetration test system. The failure characteristics of the projectiles and the coral reef limestone targets at different penetration velocities were investigated, and the influence of pore structure characteristics on penetration depth and the tunnel zone was analyzed. A penetration depth calculation model was established based on the test result, and the influence of the projectile size effect on penetration depth was discussed. [Results] The results showed that with increasing impact velocity, the degree of projectile abrasion and nose bluntness significantly increased, and a mass loss rate of 7.2% was observed at an impact velocity of 1 038.96 m/s. Within the tested penetration velocity range, the projectile and target were approximately in a rigid-body penetration state, and higher impact velocities resulted in larger crater volumes. The irregular pore distribution within the coral reef limestone targets caused projectile deflection and tunnel zone bending, Resulting in a reduction in penetration depth. Furthermore, the trajectory deflection in the tunnel zone weakened with increasing penetration velocity. Based on the penetration test data of coral reef limestone, an empirical formula for calculating penetration depth was obtained using dimensional analysis and the Levenberg-Marquardt algorithm fitting. [Conclusion] The penetration depth calculation formula for coral reef limestone can guide the design of protective layer thickness and chamber burial depth, providing theoretical references for ensuring the safety of island and reef engineering.

Keywords

coral reef limestone / penetration / model test / penetration depth formula / size effect / mechanical properties / South China Sea islands and reefs / projectile erosion