Nondestructive Evaluation of Limestone Damage Thresholds: A P-Wave Velocity–Based Approach Integrating Nonlinear Response and Crack Network Evolution

Understanding the damage evolution and strength degradation of limestone under external disturbances is critical for ensuring the stability of underground engineering structures. This study presents a comprehensive experimental investigation on the multiscale damage mechanisms and strength prediction of limestone through uniaxial compression, Brazilian splitting, and scanning electron microscopy (SEM) analysis, combined with systematic P-wave velocity monitoring. Six groups of predamaged specimens (0.2σ–0.85σ, where σ represents the maximum compressive strength) were prepared to quantify the interplay among mechanical degradation, acoustic wave response, and microstructural evolution. Results revealed that increasing predamage levels led to nonlinear reductions in uniaxial compressive strength (15.59%), elastic modulus (4.03%), and P-wave velocity (12.43%), with wave velocity decay strongly correlating with strength loss. A critical damage threshold at 0.5σ triggered a transition from isolated microcrack propagation to interconnected fracture networks, accompanied by macroscopic failure mode shifts from tensile splitting to shear-dominated cone failure. Microstructural analysis demonstrated three distinct damage phases: pore compaction (σ<0.35σ), cooperative crack growth (0.35σ<σ<0.75σ), and network collapse (σ>0.75σ). By establishing a physics-informed relationship between P-wave velocity attenuation and damage variables, we propose a novel strength prediction model incorporating wave velocity sensitivity coefficients. Validated against six lithologies, the model demonstrates superior adaptability to nonlinear damage behaviors (R2=0.78–0.98) while providing microstructurally interpretable parameters. This work advances nondestructive evaluation methodologies for rock engineering by bridging micro–macro damage mechanics with practical seismic wave–based stability assessment.