Crack Initiation and Damage Evolution of Micritized Framework Reef Limestone in the South China Sea

Triaxial compression tests are conducted for the micritized framework reef limestone, which is sampled from a reef island in the South China Sea. The lateral strain response method (LSR) is applied to figure out the crack initiation stress of the reef limestone sample under different confining pressures. With a low porosity and a high dry density, the micritized framework reef limestone has higher compressive strength compared to the rudstone and bioclastic limestone from shallow reef associated strata. Under a confining pressure of 0–8 MPa, the crack initiation stress of the specimen is estimated to be 52%–69% of the peak compressive strength. The crack initiation stress increases when the confining pressure increases. Under different confining pressures, the lateral strain of the specimen when it fails is smaller than terrigenous rocks all the time. Further analysis shows that the lateral strains of the specimen when crack initiation occurs under different confining pressures are similar (with a value of < 0.0004). Between the point of crack initiation and the point of rock dilation, the lateral strain increases in a logarithmic manner under all the confining pressures. After reaching the point of rock dilation, the lateral damage variable is estimated to be 0.56–0.74, larger than the axial damage variable. Based on the analysis of the lateral strain, an empirical relationship between the lateral damage variable and the lateral strain is proposed to portray the damage evolution of the reef limestone specimen.