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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。
The reliability analysis of single pile is the foundation of pile group reliability analysis. However, due to the different failure criteria adopted in different countries, the ultimate bearing capacity of single pile is also different, so the reliability of single pile obtained is also different. Therefore, Pile reliability is greatly affected. The failure criteria for determining the ultimate bearing capacity of single pile at home and abroad are summarized. Based on the s-lgt failure criterion adopted in China, the deviation coefficient of other failure criteria is defined. At the same time, the calculation method of pile group reliability under different failure criteria is given by using pile group effect and deviation coefficient, which provides a theoretical basis for the unified assessment of pile foundation safety. The case study shows that the reliability indexes obtained by using different failure criteria are different and vary greatly, but the reliability of group pile foundation has not changed. Therefore, when measuring the safety of group pile foundation, the failure criterion adopted must be determined first. Only using the calculation results of reliability index to measure the basic safety will bring potential safety hazard to the project. In addition, pile group effect, system effect, soil type and cap type also have a great influence on the reliability. In the reliability analysis, it is necessary to fully study and analyze it.