Evaluation of prediction models for tip resistances of rock-socketed drilled shafts

This study compiled a database called CYCU/RockTip/51 consisting of 51 rock-socketed drilled shafts installed at different sites worldwide, covering a wide variety of rock properties and shaft geometries. The tip resistances from seven representative prediction models were compared with the measured values. These measured values were obtained from the load-displacement curves of field load tests using three interpretation criteria. It was found that the prediction models of Teng, Coates, Rowe and Armitage, and ARGEMA overpredicted the measured capacity, while Zhang and Einstein, Vipulanandan et al. and Zhang are less biased. These tip prediction models also could be classified according to displacement requirements. The proposed tip prediction models of this study are presented based on different interpretation methods and the displacement ranges that they are mobilized. Finally, the normalized load-displacement curve was fitted to the hyperbolic curve with two model parameters (a and b). The parameters a and b define the reciprocal of the initial slope and the asymptotic resistance, respectively. The statistics of (b, a) for rock-socketed drilled shafts in CYCU/RockTip/51 are mean = (0.76, 1.09), COV = (0.13, 0.59), and correlation coefficient = -0.79. These statistics are useful for reliability-based design.