Abstract: To investigate the failure mode of rock layers at the pile tips of row pile and group pile foundations over undulating bedrock cavities, indoor model tests were conducted on row piles and group piles. Concurrently, the limit analysis finite element method was used to analyze the variation in ultimate bearing capacity of the rock layer at the pile tip of single-row and group pile foundations under different pile spacings. The results show that: (1)The failure shape curves of the rock mass at pile tips in group piles and piled raft foundations correlate well with those of single piles. (2)The ultimate bearing capacity of rock at pile tips in group piles and piled raft foundations over cavities is reduced when pile spacing is small and is lower than the sum of the capacities of an equal number of single piles. This reduction becomes negligible when pile spacing exceeds 5d. (3)The failure mode of rock at pile tips in group piles can be approximated as that of a large equivalent pile cap. At small pile spacings, the ultimate bearing capacity depends on the total perimeter length of the pile axis connections. Different pile layouts do not affect the ultimate bearing capacity when this perimeter length remains the same. (4)For a constant number of piles, the pile group efficiency coefficient increases with larger pile spacing until reaching 6~7d, after which it approaches 1.0. For a given perimeter length of pile axis connections, a smaller number of piles yields a higher pile group efficiency coefficient. These findings provide guidance and reference for the design and construction of pile foundations in karst areas.