<p>This study investigates the vertical bearing characteristics of single piles (cast-in-site concrete) in interactive karst foundations through indoor model tests, analyzing load–settlement curves, axial forces, average side friction distribution, end resistance and side friction proportions, and failure modes of cavity roofs. Tests covered eight conditions across three groups: single karst cavity with varying spatial distributions; interactive distribution of traversed and underlying cavities; and interactive distribution of pile-end adjacent and underlying cavities. The results revealed that: (1) At the same rock-socketing depth, compared to an underlying cavity with a roof thickness of 2d and a span of 6d, the ultimate bearing capacity for a traversed karst cavity increases by 147.1%. With an eccentric distance of 2.5d, the capacity improves by 52.9%. (2) The rock-socketed section of a traversed cavity most effectively mobilizes side friction, significantly reducing axial force there. Side friction mobilization varies considerably with the traversed cavity's position, being more effective near the pile end. Increasing the number of traversed cavities raises settlement, decreasing overall side friction mobilization and increasing end resistance. (3) Pile-end adjacent cavities have a relatively small impact on bearing capacity. However, their interactive effect with underlying cavities mobilizes side friction more effectively, though to a limited degree. With multiple cavity types present, side friction reflects combined effects. (4) For underlying cavities (2d roof thickness, 6d span), the roof failure mode is punching shear, forming a shape resembling a truncated cone. Pile-end adjacent cavities enlarge the failure zone, with a radius of at least 3d. When the underlying cavity's eccentricity reaches 2.5d, the punching shear cone expands toward the cavity interior, making the failure radius greater than 3d.</p>