To overcome the shortcomings of traditional concrete coatings, such as high roughness and poor frost resistance, this study developed and evaluated a new hydrophobic coating—modified polyurea hydrophobic coating (MPHC). MPHC features strong adhesion, high hydrophobicity and excellent durability. The coating performance was evaluated through contact angle measurement, tensile bond strength test, and assessment of environmental durability under several aging conditions including immersion, heat resistance and freeze–thaw cycles. The experimental results showed that the surface contact angle of MPHC reached 131.2°, demonstrating strong hydrophobicity. After durability testing, there was no significant decrease in contact angle and bond strength, confirming the robustness of the coating. The coating combines a “dual structure” formed by polydimethylsiloxane and microsilica powder, thereby creating a hydrophobic rough surface. This structure minimizes the fluid–solid interface area and adhesion, thereby enhancing drag reduction performance. In drag reduction tests on channel model linings, compared with ordinary concrete, MPHC reduced the roughness coefficient by 10.0–11.6%, and by 7.4–7.5% compared with ordinary polyurea coatings. The outstanding hydrophobicity, durability and drag reduction performance of MPHC make it a promising solution for improving the water conveyance efficiency of concrete-lined channels.

Densely distributed small holes significantly affect the mechanical behavior and fracture characteristics of rock masses. In this study, the two-dimensional particle flow code was employed to establish a series of numerical models of dolomitic limestone, with the number of small circular holes increasing according to the sequence (2n − 1)² (n = 1–6). Comparative models with equivalent area and variable spacing were additionally designed to explore their regulatory effects. The strength, crack evolution, and contact force chain distribution of each model were systematically analyzed. The results reveal that the number of small holes exhibits an approximately linear negative correlation with the rock strength. The number of holes dominates the crack initiation location and propagation path. The crack initiation stress gradually decreases with increasing hole number, while the ratio of crack initiation stress to peak stress exhibits a V-shaped trend. As the hole number increases, the distribution of compressive force chains shifts from the sides of holes to the vertical strips between holes, and tensile force chains become significantly enhanced in the areas above and below the holes. Hole spacing and equivalent area exert only local modulating effects; the number and spatial arrangement of holes remain the dominant controls on strength deterioration and fracture evolution. These findings offer a theoretical foundation for stability assessment in rock masses characterized by densely distributed hole defects.