毛竹管桩基坑支护可靠性研究

Study on reliability of foundation pit support with bamboo pipe pile

为研究参数不确定性对支护桩可靠度指标的影响,以桩顶容许位移和极限承载力作为毛竹管支护桩使用功能的判定标准,利用中心点法推导出正常使用极限状态和承载能力极限状态可靠度指标的计算公式,对齿状竹桩与直排竹桩支护体系桩顶位移参数进行可靠度分析。结果表明:桩顶位移承载能力极限状态可靠度指标可由正常使用极限状态可靠度指标线性表达;桩顶容许位移与计算位移的变异系数对毛竹管桩正常使用极限状态可靠度指标呈负相关,在低变异性下影响较为显著,转折点为0.2,影响程度随着变量不确定性增加而降低;在正常使用极限状态下,齿状排桩较直排桩有更优的可靠度,随着桩顶计算位移与容许位移的变异性增加,二者可靠度指标差异性逐渐减小;毛竹管桩承载能力极限状态可靠度指标随极限位移与容许位移比不确定性的减小而增大。桩顶设计位移定量时,为满足目标可靠度,可适当提高极限位移与容许位移比或降低其变异性来满足支护需求。

To explore the influence of parameters uncertainty on the reliability of supporting pile,allowable displacement and ultimate limit capacity of moso bamboo supporting pile were considered as an assessing standard of the pile performance.The calculated equations of reliability indices under serviceability limit states and ultimate limit states were conducted by using the center-point method.The reliability of displacement of pile top was analyzed in dentate row piles and single row piles.The results showed that the reliability index of the displacement under ultimate limit states could be expressed linearly by the same reliability index under serviceability limit states.The coefficient of variation between the allowable displacement and the calculated displacement was negatively correlated with the reliability index of moso bamboo piles under serviceability limit states.The impact was significant under a low degree of variation,and the turning point was 0.2.The degree of influence decreased as the uncertainty of the parameters increased.Under the serviceability limit state,the dentate row piles had greater reliability over single row piles.As the degree of variation between the calculated displacement and the allowable displacement increased,the difference of reliability between the two types of piles was gradually decreasing.Under the ultimate limit states,the reliability index of the moso bamboo piles increased as the uncertainty of the ratio of ultimate limit displacement to allowable displacement decreased.When the displacement of the pile top was fixed,increasing the ratio of ultimate limit displacement to allowable displacement or decreasing the variation of the displacement ratio are desirable to meet goal reliability and supporting requirements.