竖向受荷桩极限承载力计算的可靠性分析

Reliability analysis on ultimate bearing capacity calculation for vertically loaded piles

为深入探究竖向受荷桩极限承载力3种典型计算模型(双曲线模型、指数曲线模型和灰色理论模型)的可靠性,基于具有极限承载力的95根试桩数据,详细分析3种单桩竖向极限承载力计算模型预测行为的不确定性。研究发现3种计算模型均可基于未达到破坏状态单桩的荷载-沉降数据序列预测其极限承载力,但具有一定的不确定性。编制的计算程序SIMUPU有效提高了单桩极限承载力的计算效率,具有良好的实用性。结合程序分析结果,提出单桩竖向承载力计算模型不确定性的分析方法,阐明了计算模型不确定性的统计特征,发现计算模型的不确定性系数统计均值可用于修正并提高模型预测单桩极限承载力的可靠性。基于双曲线模型极值点法预测的单桩极限承载力普遍偏大,且离散性较大,偏于不安全;采用双曲线模型最大曲率点法确定单桩极限承载力的不确定性系数均值虽接近1.0,但其预测结果的可靠性略有降低。指数曲线模型和灰色理论模型的预测结果整体略偏小,且二者预测结果较为接近,预测所得单桩极限承载力的可靠性优于双曲线模型。基于工程试验桩的应用分析表明,单一计算模型可能产生较大误差,基于本文可靠性分析方法,同时采用3种计算模型进行预测、修正、取均值,可获得更为可靠的单桩极限承载力。研究成果可为单桩极限承载力的分析和获取提供参考和依据。

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.