Abstract: Coral-reef limestone, as a typical heterogeneous porous medium, possesses pore structures that undergo complex
evolution under external stress, which exerts a substantial control over its seepage and mechanical behaviors. To elucidate the stress-driven mechanisms governing pore evolution, three-dimensional digital cores of reef limestone were reconstructed from X-ray micro-computed tomography (micro-CT) scans of coral reef limestone specimens. Via image segmentation and geometric reconstruction, multi-dimensional pore-structure parameters were extracted, including fundamental geometric descriptors, Feretdiameter metrics, shape factors, structural anisotropy indices, and spatial-position parameters. Axial step-loading tests were performed on the core specimens across five stress stages spanning 0 to 5.4 MPa, with micro-CT scans performed at each loading step. On the basis of connectivity analysis, pores were categorized as connected pores and isolated pores. The results reveal that connected pores undergo pronounced compaction, fracturing, and reconfiguration during loading, and their morphological parameters exhibit highly sensitivity to stress changes. By comparison, isolated pores retain geometric stability and dominate total porosity variation. K-means clustering was employed to further classify the connected pore structures under different stress stages, yielding three representative pore classes: dense auxiliary pores, transitional transport pores, and primary skeletal channel pores. These pore types differ markedly in scale, connectivity, and morphology, recording a structural evolutionary pathway of “compression-collapse-reconnection.” This work establishes a multi-parameter clustering analytical framework, offering a quantitative support for deciphering pore-vug evolutionary mechanisms within limestone subjected to stress fields. 

Key words: coral reef limestone, stress evolution, Micro-CT, pore structure, connectivity, clustering analysis