海洋平台打桩过程中溜桩对桩基影响的研究

Influence of Pile Sinking on Pile Capacity during Pile Driving on Offshore Platforms

摘要:

打桩过程中突然快速的溜桩可能造成脱锤，桩体破坏，引发安全事故。由于溜桩的产生往往造成打桩锤击数的预测值与实测值具有较大的偏差，此时准确评价溜桩后桩基承载力就成为实际工程中非常关注的问题。本文选择我国东海两个工程实例，根据现场高应变动测试验和打桩记录，研究了溜桩对桩基承载力的影响。计算分析显示，溜桩的产生会导致打桩总能量的明显降低；现场动测试验结果显示，溜桩发生后在发生溜桩的土层的桩体侧摩阻力接近于零，而桩端阻力没有明显的异常，说明溜桩导致的承载力降低主要来自于侧摩阻力的减小。在本文的实例中，溜桩导致的桩基承载力的降低最大可以达到桩基承载力计算值的17%。

Abstract:

Pile sinking during pile driving is common.A sudden drop of a pile after a strike from the hammer may cause a serious accident，such as the pile falling out of the drive cap or damage to the pile from high tension stress.Pile sinking also often causes a large deviation between the drivability prediction and the measured blow count.Therefore, an accurate assessment of pile capacity after pile sinking becomes an important problem to address in practice.In this paper，two projects in the East China Sea are chosen to analyze.Based on the results of dynamic load tests in the field and pile driving records，the influence of pile sinking on pile capacity at the end of driving （EOD）is studied.The analysis results show that pile sinking will lead to a significant decrease in the total energy used in pile driving.The results from CAPWAP show that the unit friction of a soil layer where piles run off is close to zero，while the pile end resistance shows no obvious abnormalities.This indicates that the decrease in pile capacity caused by pile sinking is mainly from friction reduction.In this instance，the pile capacity reduction resulting from pile sinking can reach a maximum of 17% of the designed value.