考虑长径比和容许沉降影响的群桩SLS可靠度分析

Reliability analysis for serviceability limit state of pile groups considering pile length-diameter ratio and limiting tolerable settlement

考虑桩正常使用极限状态(SLS)和承载能力极限状态(ULS)模型不确定性,利用概率统计理论,给出2种极限状态下单桩可靠度指标间的线性关系式。并结合群桩ULS可靠度分析方法,提出群桩SLS可靠度评估方法。最后,利用试桩资料,研究桩长径比(L/D)和容许沉降(slt)对群桩SLS可靠度分析结果的影响。研究表明:L/D对群桩SLS可靠度影响显著。无黏性土条件下,当L/D≤10或20<L/D≤30时,都可取得较大的群桩SLS可靠度指标;黏性土条件下,当20<L/D≤30时,可取得较大的群桩SLS可靠度指标。随slt的增加,估计的群桩SLS可靠度指标逐渐增大,但增大幅度逐渐减小,特别是当slt大于25 mm以后,随slt的增加,群桩SLS可靠度指标变化很小,此时承载力因素在桩基可靠度设计中起决定作用。

The model uncertainties for serviceability limit state （SLS） and ultimate limit state （ULS） of piles were considered in order to establish a linear equation between the reliability indices for SLS and ULS of single piles using the probability and statistics theory. Then a method was presented to evaluate the reliability for SLS of pile groups in combination with the method of reliability analysis for ULS of pile groups. Finally, the influence of pile length-diameter ratio （L/D） and limiting tolerable settlement （slt） on the reliability analysis for SLS of pile groups was studied utilizing pile test data. The case study indicates that there existed the significant impact of L/D on the reliability indices for SLS of pile groups. And for non-cohesive soils, when L/D was smaller than 10 or between 20 and 30, the larger reliability indices for SLS of pile groups could be achieved. For cohesive soils, when L/D was between 20 and 30, the larger reliability indices for SLS of pile groups could be obtained. In addition, the reliability indices for SLS of pile groups generally increased with an increase of slt although the increase rate gradually diminished. Especially for slt exceeding 25 mm, the variation of the reliability indices for SLS of pile groups was very small. So for larger slt values, the ULS designs rather than the SLS designs played a decisive role in the reliability-based design of pile foundations.