Ultimate bearing capacity of intact rocks at tip of large-diameter rock-socketed piles considering internal micro-cracks

Abstract

In the design of large-diameter rock-socketed piles, the ultimate bearing capacity of intact rocks under the pile tip (qb ) is often required to be predicted, especially for rock-socketed end-bearing piles. Existing approaches for calculating qb establish an empirical relation with the macroscopic parameters of rock layers, but the research on the microscopic parameters inside intact rocks is insufficient. This study provides a theoretical method for calculating qb from a micro perspective and implements it in MATLAB, in which the integral stress of the Mindlin solution within the circular region at the pile base was selected as the stress state of the theoretical calculation regions, and the tension– or compression–shear mixed mode I–II criterion was selected as the failure criterion of micro-cracks inside intact rocks. Six model piles with measured ultimate end-bearing capacities were analyzed to validate the proposed solution. The results showed that the failure ranges of intact rocks under an identical base load for analytical analyses are comparable with those obtained by model tests, which confirms the rationality of the theoretical approach. Then, the failure zone of intact rocks under different working loads of pile base was explored. Finally, parametric studies were conducted using the proposed solution to explore the effects of rock properties and pile dimensions.