海洋平台大直径超长桩成桩机理研究

THE FORMATION MECHANISM OF SUPER LARGE DIAMETER AND DEEP PENETRATION PILE IN OFFSHORE PLATFORM

  • 摘要: 随着海洋平台上部结构的增大,大直径超长的钢管桩越来越多的被应用于实际工程当中。在打桩过程中,往往会因为各种原因而造成停锤。停锤后打桩的再起动问题是一个决定桩基能否打入到设计深度的关键问题,与桩的承载力恢复密切相关。为对这一问题有深入认识,通过对某实际打桩工程出现的问题进行研究,根据地质勘察结果,对该地区的土体特点进行了分析;根据打桩实测纪录,分析了桩端阻力和侧摩阻力对打桩影响。同时根据打桩记录和现场试验,计算了打桩过程中的实际土抗力并对土抗力随时间的变化进行了探讨。分析显示,桩的可打入性与土质条件密切相关;超大直径超长桩在打入过程中形成完全闭塞土塞的可能性不大,连续打桩中的侧摩阻力平均为静止侧摩阻力的0.68;打桩中6周的停锤,使得土抗力比连续打桩的土抗力至少增加了将近65%,停锤3个月后的土抗力超过了初始静承载力,桩的承载力随时间增长的趋势明显。

     

    Abstract: With the platform size increase, the super large diameter and deep penetration pipe piles are increasingly used in practice. Pile driving maybe suspended because of many reasons during installation. Whether the driving could re-strike or not is an important problem that many people concerned,and it is related to pile capacity set-up. Based on a case study, the characteristics of the soil in this area are summarized, and the influence of end bearing and skin friction on pile driving are analyze. At the same time, the soil resistance is calculated and the change of soil resistance with time is discussed according to driving record and in situ tests. It is found that the soil properties play a very important role in pile driving. For the super large diameter and deep penetration pipe pile, the soil in the pile is not plugged completely, and the average ratio of skin friction in continuous driving to static skin friction is 0.68. The soil resistance increases about 65% after a driving suspension of about 6 weeks. After 3 months driving suspended, the soil resistance is greater than the static bearing capacity, and the increment of pile bearing capacity with time is very obvious.

     

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