Controlling blast-induced damage is important for underground construction in island and reef engineering. This paper investigates the transient strain response and damage evolution of reef limestone under radially decoupled charging through laboratory model blasting experiments and three-dimensional numerical simulations. Cylindrical reef limestone specimens with radial decoupling coefficients $K_{d}$ of 1.0, 1.25, 2.0, and 2.5 were tested. Strain gauges were used to record blast-induced strain histories, while post-blast crack patterns were analyzed using image processing and box-counting fractal analysis. The results show that $K_{d}$ has a significant non-monotonic effect on peak tensile strain, crack development, and fractal dimension. The peak tensile strain increased from 2.09 $\upmu \varepsilon $ at $K_{d} = 1.0$ to a maximum of 2.28 $\upmu \varepsilon $ at $K_{d} = 1.25$ , then decreased to 1.13 and 0.99 $\upmu \varepsilon $ at $K_{d} = 2.0$ and 2.5, respectively. The crack network also reached its highest fractal dimension of 1.5799 at $K_{d} = 1.25$ , indicating the most developed multiscale cracking pattern. Numerical simulations further show that increasing $K_{d}$ attenuates stress-wave amplitude, modifies wave propagation, and promotes a transition from extensive crack development to more localized damage near the blasthole. These findings suggest that an intermediate radial decoupling coefficient, particularly $K_{d} = 1.25$ , can provide a favorable balance between blasting efficiency and damage control in porous reef limestone. The results provide guidance for precision blasting design and damage mitigation in reef-island underground engineering.
