Progressive failure and fracture characteristics of coral reef limestone under triaxial compression

Coral reef limestone (CRL) is a distinctive type of rock formation characterized by a highly developed pore structure that exhibits inherent anisotropy, resulting in mechanical behaviors that differ from traditional terrestrial limestone. This study investigates the mechanical properties and progressive failure characteristics of two types of CRL: one with fine pores (CRF) and the other with coarse pores (CRC), using triaxial compression tests combined with CT scanning techniques. The study explores the influence of pore structure characteristics and discusses differences in microstructure, mechanical properties, and failure modes between coral reef limestone and terrestrial limestone. The results reveal that the stress–strain behavior of CRL exhibits distinct multi-peaks and relatively high residual strength, following a recurring four-stage failure phenomenon attributed to the continuous load-bearing of the residual skeleton. The peak strength of CRF is positively correlated with density and confining pressure, while CRC exhibits a stronger structural dependence, with peak strength and longitudinal wave velocity significantly influenced by the inclination angle of growth lines. CRF tends to fail in regions with a dense distribution of pores, resulting in a complex crack network, while CRC’s failure is concentrated in weak zones between large defects and growth lines. By defining multi-stage damage factors, the study quantifies the damage extent at each stage, which correlates with the number of main cracks. These findings provide new insights into the failure mechanisms of coral reef limestone in complex stress environments and offer important theoretical support for related engineering design.