基于不排水强度的海洋钢管桩竖向受荷设计方法及应用

su-based Design Method of Offshore Pipe Pile under Vertical Loading and its Application

海洋工程中使用最广的是钢管桩,黏土中钢管桩的竖向承载力的主要贡献为桩侧阻,侧阻的合理计算对桩基承载力十分关键。在对国外应用较广的基于不排水强度的桩基设计方法进行综述与可靠性评价的基础上,结合海洋大直径钢管桩的工程案例,分析不同设计方法在海洋大直径桩中应用的合理性与不足,提出计算参数的取值原则与试验确定方法。根据桩基数据库与海洋大直径钢管桩的工程案例分析结果,表明基于不排水强度的API法计算结果可靠性变异性较大,存在承载力计算值偏大的不安全问题,经改进后的Fugro法与NGI法相对偏安全,可应用于海洋大直径桩,但不排水强度的确定十分关键。由于海洋土易扰动,室内试验宜采用SHANSEP法来获取不排水强度,且结合原位静力触探试验来综合确定不同深度、不同土层的不排水强度。

Pipe piles are widely used in offshore project.The shaft friction in clay is essential to bearing capacity of pipe piles.Reasonable selection of design methods and parameters is very important for offshore piles.By focusing on the current popular vertical load design methods based on undrained strength for offshore piles,various design methods of pile in clay were summarized.And based on the database,the accuracy and reliability of methods were reviewed.A field test of full scale offshore pile was carried out and analyzed.By comparing the calculated and the measured capacity for each method,the reliability of various design methods was evaluated for large diameter piles,and reasonable suggestions for design methods and parameters determination are given.The results show that the API method based on undrained strength has large reliability variability,and there is an unsafe problem that the calculated bearing capacity may be a bit large.The improved Fugro method and NGI method are relatively safer and can be applied to large diameter pile,but the determination of undrained strength is very critical.Because the offshore clay is easily disturbed,the laboratory test should adopt the SHANSEP method to obtain the undrained strength,and combine the CPT to comprehensively determine the undrained strength of different depths and different soil layers.