大直径钢管桩非连续打桩过程中拒锤原因的分析研究

 在大直径超长钢管桩施工过程中，往往会因为接桩或施工调配等原因出现停锤，实际工程中，由于各种原因造成停锤后桩体无法继续顺利打入的情况屡屡发生，因此对这一问题的解决就成为决定打桩工程是否成功的关键。采用有限元动力分析方法对连续打桩过程中砂土中的孔压和有效应力的变化进行研究，对停锤所造成的后续打桩困难的机制进行探讨。同时利用工程实测数据对有限元分析得到的结论进行进一步讨论和验证。动力有限元分析的结果显示，连续打桩会造成桩周土残余孔压的明显累积；如果出现停锤，砂土中超静孔隙水压力消散速度很快，导致桩端1～2倍桩径范围内的有效应力的显著变化，造成桩端阻力的明显提高，而打桩对桩侧摩阻力的影响主要集中在振源附近区域。工程实测数据证实，停锤3个月后，砂土中的土阻力增长明显，尤其是桩端处的砂土层。而处于黏土层中间的薄砂层固结程度明显降低。在进行打桩预测时，对于停锤造成的侧摩阻力的提高应该考虑打桩的影响范围和固结时间，对于桩端阻力的提高应该考虑复打过程的影响。

STUDY OF PREMATURE REFUSAL OF LARGE DIAMETER PIPE PILE CAUSED BY PILE DRIVING SUSPENDING

With the platform size increment，the large diameter pipe piles are used in practice more and more. Pile driving maybe suspended because of many reasons during installation. Whether the driving could be re-started or not is an important problem that many people concerned. In this paper，we study the change of excess pore water pressure and effective stress during continuous and discontinuous striking with dynamic FEM. Based on FEM results，the mechanics of premature refusal caused by pile driving suspending in sand layers is discussed combined with a practical case. The results of dynamic FEM present that continuous driving causes pore water pressure accumulating around the pile tip. If the pile driving suspends，the excess pore water pressure dissipate quickly to cause the effective stress changes obviously within 1–2 times of the pile diameter. The end soil resistance increase，but the change of friction is just near the vibration fountain. The measurement data of the practical case show that after 3 months suspending，the friction in sand layer recovered and exceeded initial value，especially near pile tip. The friction increment is small in the thin sand layer between two clay layers. The friction in clay layer is still lower than the initial value. When we predict soil resistance after suspending，for the friction，the effecting scale of driving and suspending time should be considered；for the end resistance，the restarting procedure is important.