基于不同失效准则的群桩可靠度分析

单桩可靠度分析是群桩可靠度分析的基础，但是由于各国采用的失效准则不同，得到的单桩极限承载力也不同，从而求出的单桩可靠度也不同，因此失效标准的选取对群桩可靠度影响很大。整理了国内外确定单桩极限承载力的失效准则，以国内习惯采用的 s – lgt 失效准则为基准，定义其他失效准则的偏差系数。同时利用群桩效应和偏差系数给出了不同失效准则下群桩可靠度的计算方法，为统一评价桩基安全提供了理论依据。算例分析表明：采用不同的失效准则得出的可靠度指标不同，且相差较大，但是群桩基础的可靠性并没有改变。因此，在衡量群桩基础的安全性时，要先确定采用的失效准则，仅利用可靠度指标的计算结果衡量基础的安全性会给工程带来安全隐患。另外群桩效应、系统效应、土体类别和承台类型对可靠度也有较大影响，在可靠度分析时，要对其进行充分的研究和分析。

Reliability analysis of pile groups based on different failure criteria

The reliability analysis of a single pile is the basis of reliability analysis of pile groups.However,the ultimate bearing capacity of the pile and the reliability index obtained using different failure criteria may not be the same due to the differences in failure criteria used in different countries.Therefore,the reliability of pile groups is various according to different failure criteria.The different failure criteria from various countries are examined,and a bias factor defined with respect to s-lgt criterion usually used in China is introduced.Meanwhile,the calculation method of reliability of pile groups considering different criteria is presented using the bias factors and pile group effect,which provides a theoretical basis to calibrate the reliability levels of pile foundation associated with various failure criteria.The results from case studies indicate that considerable reliability index of pile groups can be obtained according to different failure criteria,but the safety of pile group foundation is not variable.Therefore,before judging the safety of pile group foundation,the failure criterion should be chosen,and it can cause relatively significant loss to the project if the calculated reliability index is only used to evaluate the safety of foundation.In addition,the pile group effect,system effect,soil type and cap type have significant influences on the reliability of pile group foundation.Therefore,their contribution to the reliability should be considered in the reliability analysis of pile group foundation.