Experimental Investigation of Damage Evolution Characteristics of Coral Reef Limestone Based on Acoustic Emission and Digital Volume Correlation Techniques

The variation of pore structure results in a significant difference in physical–mechanical properties within coral reef limestone (CRL). The acoustic emission (AE) and digital volume correlation (DVC) techniques were utilized to investigate the damage evolution characteristics of four structural types of CRL under uniaxial compression. The influence of pore structure on the fracture mechanism of CRL was revealed from the microscopic perspective. The results suggested that the failure patterns of CRL specimens gradually transferred from brittle tensile failure to ductile shear failure with the increase of porosity. Based on the AE technique, the damage evolution process of CRL was comparatively analyzed. The AE evolution characteristics of the coral framework limestone (CFL) and coral boulder limestone (CBL) were similar to conventional brittle rocks. Furthermore, the coral gravel limestone (CGL) and coral calcarenite limestone (CCL) stimulated a considerable amount of AE signal during the initial compression stage by adjustment of sand particles. Using the computerized tomography (CT) scanning-based DVC method, the strain field distribution after the failure of CRLs with different structures was revealed, and the interaction mechanism between pore and crack was analyzed. Finally, the crack volume strain (CVS), lateral strain response (LSR), and AE cumulative energy were used to determine the crack initiation stress range in CRLs of four structures. According to the range of crack initiation stress, the results obtained by the on-site microseismic monitoring and in-situ stress measurement can be used to determine the stress state and plastic zone extent in the coral reef strata, which provides a reference for the design of support schemes in the construction of island reefs.