大厚度湿陷性黄土场地铁路桥梁灌注桩负摩阻力计算方法  

Calculation Method of Negative Skin Friction of Railway Bridge Cast-in-Situ Pile in Large Thickness Collapsible Loess Area

作　　者：张延杰[1] 杨成成 王旭[1,2] 杨少军 蒋代军 ZHANG Yanjie;YANG Chengcheng;WANG Xu;YANG Shaojun;JIANG Daijun(School of Civil Engineering,Lanzhou Jiaotong University,Lanzhou Gansu 730070,China;National and Provincial Joint Engineering Laboratory of Road&Bridge Disaster Prevention and Control,Lanzhou Gansu 730070,China;China Railway First Survey and Design Institute Group Ltd,Xi′an Shaanxi 710043,China)

机构地区：[1]兰州交通大学土木工程学院,甘肃兰州730070 [2]道桥工程灾害防治技术国家地方联合工程实验室,甘肃兰州730070 [3]中铁第一勘察设计院有限公司,陕西西安710043

出　　处：《中国铁道科学》2023年第5期94-102,共9页China Railway Science

基　　金：国家自然科学基金资助项目(52268058);中央引导地方科技发展资金资助项目(22ZY1QA005);兰州交通大学“天佑青年托举人才计划”基金资助项目。

摘　　要：当铁路桥梁桩基穿越大厚度湿陷性黄土场地时,桩基负摩阻力和中性点深度的合理取值与计算,是目前需要解决的工程难题。针对现行规范的不足,在分析总结湿陷性黄土场地桩基浸水试验结果的基础上,采用抛物线拟合负摩阻力达到稳定状态时的分布,并对中性点深度比、负摩阻力最大值出现深度、负摩阻力最大值与平均值等参数进行分析与探讨;根据负摩阻力的力学机理与分布模式,考虑湿陷性土层厚度对动摩擦系数的影响,提出负摩阻力计算方法。结果表明:浸水前桩顶承受一定竖向荷载时,湿陷性黄土层下限深度采用室内试验计算值,确定的中性点深度比与现行规范推荐值较为一致;负摩阻力最大值出现深度基本为中性点深度的0.5倍,负摩阻力最大值为其平均值的1.5倍;采用该方法计算的负摩阻力平均值与《湿陷性黄土地区建筑灌注桩基技术规程》推荐值较为一致,可作为大厚度湿陷性黄土场地灌注桩单桩竖向承载力计算时的特征值,研究结果可为湿陷黄土地区的桩基工程设计提供参考。When the pile foundation of a railway bridge crosses large thickness collapsible loess site,the reasonable value and calculation of negative skin friction and neutral point depth of pile foundation are key engineering challenges that need to be resolved at present.In view of the shortcomings of the current specifications,based on the analysis and summary of the immersion test results of the pile foundation on the collapsible loess site,parabola is used to fit the distribution of negative skin friction when it reaches a stable state,and the parameters such as the depth ratio of the neutral point,the depth of the maximum negative friction,the maximum and the average values of negative skin friction are analyzed and discussed.According to the mechanical mechanism and distribution mode of negative skin friction,considering the influence of collapsible soil thickness on dynamic friction coefficients,the calculation method of negative skin friction is proposed.The results show that when the pile top bears a certain vertical load before immersion,the neutral point depth ratio determined with the lower limit depth of collapsible loess layer calculated by laboratory test is consistent with the recommended value of the current specification.The depth of the maximum negative friction is about 0.5 times the depth of the neutral point,and the maximum value of negative skin friction is 1.5 times of its average value.The average value of negative skin friction calculated by the proposed method is consistent with the recommended value in“Technical Specification for Building Cast-in-Situ Pile Foundations in Collapsible Loess Regions”,which can be used as the characteristic value for calculating the vertical bearing capacity of single pile in large thickness collapsible loess sites.The research results can provide reference for the engineering design of pile foundation in collapsible loess areas.

关 键 词：铁路桥梁 桩基 湿陷性黄土 灌注桩 负摩阻力 

分 类 号：U443.15[建筑科学—桥梁与隧道工程]