Abstract: For piles above underlying karst caves, the ratio of rock-socketed depth to cave roof thickness (rock-socketed ratio) can be high in certain projects. To study the influence of karst cave roof thickness on the vertical bearing characteristics of piles with high rock-socketed ratio, load tests were conducted on model piles with a rock-socketed ratio of 0.5, while the cave roof thickness was gradually increased from one to five times the pile diameter. Based on the test results, an analysis model for the ultimate bearing capacity of the pile was proposed, and a calculation formula was derived using the limit equilibrium principle. The results show that: (1) The failure mode of karst cave roof is trumpet-shaped punching failure, and the dimensionless fitting function for the fracture surface can reasonably predict the range of roof fracture. (2) The load-displacement curve at the pile top exhibits a steep change type, with an approximately linear relationship before the steep change point. (3) As the roof thickness increases, the ultimate bearing capacity of the pile increases nonlinearly, and the proportion of pile tip resistance supporting the upper load rises from 35.4% to 72.4%. (4) The relative error between the ultimate bearing capacity calculated by the proposed method and the test value ranges from −12.8% to 12.1%, indicating the method’s good rationality.

Key words: rock-socketed pile, underlying karst cave, cave roof thickness, vertical bearing characteristics, model test