Reliability analysis on ultimate bearing capacity calculation for vertically loaded piles

To deeply investigate the reliabilities of three typical calculation models (hyperbolic model, exponential model, and grey theory model) for the ultimate bearing capacity of vertically loaded piles, detailed analyses on the predictive uncertainties of the three vertical ultimate bearing capacity calculation models was conducted based on data from 95 test piles with measured ultimate bearing capacities. The results indicate that the three calculation models can predict the bearing capacity based on the load-settlement data of piles that have not yet reached a failure state, but the predictions still have certain uncertainties. The compiled computational program SIMUPU effectively improves the calculation efficiency of the ultimate bearing capacity of single piles and exhibits good practicality. In combination with the analysis results of the program, an analysis method is developed for evaluating the uncertainties of the calculation models. The statistical characteristics of the uncertainties in the calculation models were elucidated, and it was found that the statistical means of the uncertainty coefficients in the calculation models can be used to correct the predicted ultimate bearing capacity of a single pile and enhance the prediction reliability. Predictions based on the extreme point method of the hyperbolic model generally overestimate the ultimate bearing capacity of the pile, and exhibit a larger degree of dispersion, which tends to be unsafe. The mean uncertainty coefficient for determining the ultimate bearing capacity using the maximum curvature point method of the hyperbolic model is close to 1.0, but the reliability of the predictions is slightly reduced. The predictions from the exponential model and grey theory model generally slightly underestimate the ultimate bearing capacity of the pile, with the yielded results close to each other, and the reliability of the predicted results from these two models is superior to that of the hyperbolic model. Application analysis based on test piles in field suggests that a single calculation model may introduce significant errors. In light of the reliability analysis method, simultaneously employing the three computational models for prediction, correction, and taking the mean value can yield a more reliable ultimate bearing capacity of the pile. These findings provide a reference and basis for the analysis and determination of the ultimate bearing capacity of single piles. © 2024, Central South University Press. All rights reserved.