基于透明土试验的带承台缩径基桩承载力的可靠度研究

Reliability analysis of bearing capacity for necking pile with cap assisted by transparent soil experiment

基桩易产生缩径缺陷,限制桩的侧摩阻力发挥,导致桩承载力可靠度指标降低,给工程造成安全隐患。基于透明土试验,对1根完整桩及7根带承台缩径基桩(缩径桩)进行竖向加载试验,分析缩径桩承载力折减系数的变化规律。利用全概率公式分析缩径参数(长度、位置和直径)对可靠度指标的影响规律。然后,利用MatPIV程序对桩周土体颗粒的散斑场进行处理,得到桩周土体变形规律,揭示缩径限制桩侧摩阻力发挥导致可靠度指标降低的原因。研究表明:承载力折减系数与可靠度指标变化趋势一致,随着缩径长度的增加、缩径位置距离桩顶越近、缩径直径的减小,承载力折减系数与可靠度指标越小,基桩承载力损失越严重。

It is easy that the pile develops necking which can limit pile shaft resistance and cause the reliability index of bearing capacity for piles to reduce resulting in safety hazards to the project.Transparent soil technology is incorporated to load vertically on one intact pile with cap and seven necking piles with caps and the reduction coefficient of bearing capacity is investigated.The total probability formula is employed to investigate the influences of necking parameters(length,location,and diameter)on the reliability index of pile capacity.Subsequently,the speckle field of soil around piles is treated assisted with MatPIV software to obtain the soil displacement around piles,then the reduction reasons of reliability index caused by the necking to limit piles shaft resistance is explained.The study shows that the load capacity reduction coefficient and the reliability index change in the same trend,with the increase of the neck length,the closer the neck location to the top of the pile,the smaller the load capacity reduction coefficient and the reliability index,the more severe the loss of bearing capacity of the pile.