考虑桩底沉渣的基桩竖向承载力目标可靠度

桩底沉渣厚度超过一定数值后,会影响基桩尤其是端承桩桩端阻力的发挥,进而对承载力可靠度指标和目标可靠度指标造成不利影响。本文利用全概率计算公式推导出考虑沉渣桩的竖向承载力可靠度指标计算公式,并利用可靠度理论和数理统计方法给出了计算公式中每个参数的计算方法。在此基础上,推到出考虑沉渣桩的承载力目标可靠度指标计算公式。通过实例分析了不同沉渣参数(厚度、压缩模量、粘聚力、内摩擦角和泊松比)条件下,竖向承载力可靠度指标的变化规律。研究了沉渣桩出现概率对考虑沉渣桩的承载力可靠度指标和目标可靠度指标的影响规律。研究表明：沉渣的存在大大降低了沉渣桩的竖向承载力可靠度指标;沉渣厚度和压缩模量对可靠度指标有显著影响,粘聚力、摩擦角和泊松比对可靠度指标影响很小。沉渣桩的出现概率对考虑沉渣桩的承载力可靠度指标和目标可靠度指标有显著影响,尤其当概率值较大时,基础会出现一定的安全隐患。

Target Reliability Index Study of piles considering Toe Debris

The tip resistance is contingent on the characteristics of toe debris when the thickness of toe debris is larger for piles, which can cause bad results to reliability index and target reliability index. This paper employs the total probability formula to derive the computation formula of reliability index for vertical pile capacity considering the attendance of toe debris piles. Each parameter in above formula is obtained according to reliability theory and mathematical statistics method. Based on case study, the influence regulations of the toe debris parameters(eg. thickness, compression modulus, cohesive strength, internal friction angle and Poisson"s ratio) on reliability index of toe debris piles are captured. Then the probability of toe debris piles is taken into account to study the reliability index and target reliability index. The results show that the reliability index of toe debris piles greatly reduces due to the attendance of toe debris. The reliability index of toe debris piles is sensitive to the thickness and compression modulus of toe debris. However, the cohesive strength, internal friction angle and Poisson"s ratio of toe debris have less influence on reliability index of toe debris piles. The probability of toe debris piles contributes greatly to the reliability index and target reliability index, especially when the probability of toe debris piles is large, the safety of pile foundation will be threatened.