Abstract: To investigate the impact of dry-wet cycles on damage and failure characteristics of karst-fissured limestone, we prepared limestone specimens with fracture-shaped, elliptical, mushroom-shaped, and dumbbell-shaped karst fissures for uniaxial compression test. Digital Image Correlation and Acoustic Emission techniques were also employed to monitor the damage and deformation characteristics of karst-fissured limestone after 0, 3, 6 and 10 dry-wet cycles. The results showed that the dry-wet cycles and the karst fissure damage degree of limestone samples were defined based on the peak strength. The damage degree was proportional to the number of cycles and the water-rock contact area, ranging from 33.31% to 64.86% during dry-wet cycles. We expressed the coupling relationship between the damage degree of karst fissure and the dry-wet cycle. Under dry-wet cycles, the failure mode of karst-fissured limestone changed from tensile failure to tensile-shear mixed failure, and the local zone of surface strain transitioned to ductile extension. The shape of karst fissure had a dominant guiding effect on the failure path. In addition, the cumulative ringing counts of acoustic emission, as well as the crack initiation stress σ_ci and crack damage stress σ_cd decreased with the proceedings of dry-wet cycles. The research results provide scientific basis for analyzing the failure mechanism of karst-fissured limestone in the Three Gorges Reservoir area.

Key words: karst-fissured limestone, fracture evolution, mechanical damage, dry-wet cycles, uniaxial compression, digital image correlation, failure mechanism