打入桩承载力确定方法对安全系数的影响

Effect of driven pile bearing capacity determination methods on safety factors

在传统的容许应力设计方法中桩基承载力安全系数取决于桩基承载力的确定方法,然而,基于经验选择的承载力安全系数缺少理论依据,为此,基于贝叶斯理论和线性回归方法提出了评价桩基承载力确定方法对承载力安全系数影响的方法,给出了现行规范对于不同承载力确定方法采用不同安全系数的理论依据,阐明了桩基动力测试降低安全系数的理论依据,并以7种桩基设计方法为例,分析了承载力确定方法对安全系数的影响。结果表明,采用所提出的方法计算的安全系数基本上与现行的经验值相一致,表明精确的承载力确定方法可以有效地降低承载力安全系数,设计方法、承载力确定方法和水平都对安全系数有影响,但当承载力试验桩的数目足够多时,安全系数对于设计方法的精确性不敏感。

In the conventional allowable stress design approach for driven piles, the safety factor is highly dependent on the accuracy of pile bearing capacity determination methods. However, the empirical safety factors may not be on a reliability basis. This paper proposes a procedure to investigate the effect of pile bearing capacity determination methods on the safety factors of driven piles, and provides a theoretical basis to verify and support existing empirical safety factor used to account for the effect of pile capacity determination methods. The procedure is formalized in the Bayesian framework. In particular, how the safety factor can be reduced based on on-site dynamic pile tests are addressed. Seven design methods for driven piles are investigated to illustrate the proposed procedure. The results indicate that the required safety factors obtained from this study are consistent with the existing empirical values. The required safety factors can be reduced considerably using more accurate pile capacity determination methods, which depends on design methods, pile capacity determination methods, and the level of pile capacity verification implemented. After sufficient pile capacity determination, the required safety factors for different design methods are not sensitive to the accuracy of the individual design methods.