## 4 Crack Growth Analysis  
The crack aggregation, propagation, and failure behaviors on the surface of the specimens can be precisely reflected by the evolution characteristics of the deformation field [37; 38]. Hence, the digital image correlation technique (DIC) was employed to capture the displacement variations of specimens throughout the compression process, and the alterations of the principal strain field of the three types of hole-fissured sandstones under different stress levels under uniaxial compression conditions with varying numbers of wetting-drying cycles were explored. Five stress state points (10%\(\sigma_{\rm c}\), 50%\(\sigma_{\rm c}\), 70%\(\sigma_{\rm c}\), 90%\(\sigma_{\rm c}\), 100%\(\sigma_{\rm c}\)) prior to the peak stress (\(\sigma_{\rm c}\)) were selected for analysis. Figure 5 depicts the evolution characteristics of the tensile strain of specimens with 0 wetting-drying cycles. By comparing the strain diagrams of the three types of hole-fissured samples, it can be seen that at the initial loading stage (10%\(\sigma_{\rm c}\)), the sample is in the pore-crack compaction stage, at which point the strain is small and randomly distributed. As the load increases to 50%\(\sigma_{\rm c}\), the samples at different horizontal distances exhibit different strain characteristics. For the 0 mm sample, two strain localization bands parallel to the loading direction are formed at the upper and lower rock bridges. Local strain concentration zones only formed in the 5 mm sample above and below the cavity and around the fracture. There is no obvious strain concentration in the 10 mm samples. When  
Taking the 5 mm samples as a representative case, the impact of the wetting-drying cycles on these deformation characteristics of hole-fissured sandstone was analyzed through horizontal displacement cloud maps (Figure 6). As shown in the figure, with increasing load, the horizontal displacement distribution shifts from a uniform pattern to a pronounced stratification at the rock bridge, indicating a progressive tendency for the sample to experience separation at both the left-hand and right-hand extremities. Furthermore, a comparative analysis of the displacement maps before and after the wetting-drying cycles reveals that a growing count of cycles exacerbates the left-right separation and fracture, resulting in more extensive damage to the samples. After 20 cycles, the maximum horizontal displacement exceeds 1.3 mm. Figure 5: Principal strain nephograms of specimens with different horizontal distances: (**a**) specimens with a lateral distance of 0 mm; (**b**) specimens with a lateral distance of 5 mm; (**c**) specimens with a lateral distance of 10 mm. Figure 7 illustrates the crack growth characteristics of each sample following complete failure after the wetting-drying cycles. Based on these observed crack growth morphologies, the breakdown patterns can be classified into three categories: tensile crack (T), shear crack (S), and mixed tensile-shear crack (T-S) [39]. As depicted in the diagram, the breakdown pattern of the 0 mm sample after 0 wetting-drying cycles is predominantly tensile failure, occurring parallel to the loading direction. Tensile failure cracks initiate at the rock bridge of the sample, propagating both upward and downward, ultimately spanning the entire sample. This behavior highlights the interaction between the crack growth path and the internal rock structure under tensile stress. After 10 wetting-drying cycles, combined tensile-shear fractures emerge at the external ends of the specimen fractures, accompanied by the development of a shear fracture on the left side of the specimen. This signifies that the moisture-desiccation cycles gradually change the internal stress distribution within the rock, transitioning the breakdown mode from a purely tensile breakdown to a more intricate tensile-shear combined breakdown.