海上隔水管锤击作业溜桩预测方法及预防措施

Prediction of slip pile during offshore riser pile driving and its preventive measures

针对海上隔水管锤击作业中的溜桩现象进行了机理分析,认为被海水饱和的、渗透性较差的粉、细砂土在隔水管的振动荷载作用下发生土液化现象是导致打桩过程中发生溜桩的原因。建立了考虑土液化现象的桩周土阻力模型,再结合波动方程提出了一种海上隔水管锤击作业溜桩预测方法。实例计算与实测结果对比显示,本文方法不仅能够更为准确地进行隔水管贯入度分析,还能成功预测打桩过程中的溜桩现象,总溜桩长度相对误差仅为2.9%,总锤击数相对误差仅为4.9%。借鉴海上风力发电机打桩过程设计了一种新的隔水管锤击作业装置,该装置能够在发生溜桩时通过及时增加锤击阻力来弥补由于土液化现象而削弱的桩周土阻力,从而阻止溜桩的发生。

Aimed at the slip pile phenomenon during offshore riser pile driving, the mechanism was analyzed and conclusion was made that saturated silt sand and thin soil with low permeability under the riser vibra- tion can generate soil liquefaction. The soil liquefaction will lead to slip pile. We integrated the liquefaction phenomenon into the traditional model of soil resistance and established a new and upgraded model. Then combining with the wave equation, we developed a prediction method for the slip pile during offshore riser pile driving. By using this new method we conducted a real case calculation and compared the calculation results with the measured results. The comparison indicated that the new method not only analyzes the riser penetra- tion more accurately but also predicts the slip pile during offshore riser pile driving successfully. The total rela- tive errors in slip pile amplitude and blow counts are 2.9% and 4.9% respectively. In addition, we designed a prototype of offshore riser pile driving equipment using pile driving for offshore wind power generators for reference. The new equipment can make up for the soil resistance slacking down, which is caused by the soil liquefaction, by increasing the resistance in time and hence prevent slip pile ultimately.