采用不同失效准则的桩基可靠度分析

桩基的极限承载力通常是根据失效准则来确定的。由于各国采用的失效准则不同，得到的极限承载力也不同，从而获得的可靠指标也不同。因此，有必要分析和比较不同失效准则对桩基可靠性的影响，以及根据桩基技术规范采用的S-lgt失效准则确定可靠指标的状况。为此，以S-lgt失效准则为基准，引进了失效准则的偏差系数的概念，根据一组实测钻孔桩数据对另外6种失效准则的偏差系数进行了评估，进而进行了可靠度分析。结果表明，不同失效准则具有不同的偏差系数，桩基可靠度明显地受失效准则的影响。根据S-lgt失效准则确定的可靠度在7种失效准则中是偏大的，不同失效准则确定的相同名义可靠指标的桩基的实际可靠性是不一样的。

Reliability analysis of pile foundations considering different failure criteria

The ultimate capacity of piles is always determined using a failure criterion. Due to the differences in failure criteria, the ultimate capacity of piles and the reliability index obtained using different failure criteria may not be the same. It is necessary to analyze the reliability levels corresponding to various failure criteria, especially S-lgt criterion used in Chinese technical code for building pile foundations. For this purpose, a bias factor defined with respect to S-1gt criterion is introduced; and one database for static load tests of bored piles is utilized for detailed evaluation of the bias arising from failure criteria, the corresponding reliability are further analyzed. The results indicate that there is a considerable bias of different failure criteria. Moreover, the failure criteria have a significant influence on the reliability of pile foundations. The reliability index based on S-1gt criterion is on the high side among seven failure criteria used in this paper. The actual safety levels of designs with the same nominal reliability index are not the salne.