赛车道软土路基PHC桩负摩阻力中性点的时间效应  

TIME DEPENDENCE OF NEUTRAL POINT POSITION IN A PHC PILE SUPPORTED SOFT SUBGRADE OF MOTOR-RACING CIRCUIT

作　　者：张先伟[1] 刘新宇 王港 常志雄 刘智海 余敦猛 李悦 ZHANG Xianwei;LIU Xinyu;WANG Gang;CHANG Zhixiong;LIU Zhihai;YU Dunmeng;LI Yue(State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences,Wuhan 430071,China;University of Chinese Academy of Sciences,Beijing 100049,China;Wuhan Smart Ecological Construction Investment Co.,Ltd.,Wuhan 430000,China;Wuhan Municipal Engineering Design&Research Institute Co.Ltd.,Wuhan 430000,China;Wuhan Zhonghe Engineering Technology Co.,Ltd.,Wuhan 430000,China)

机构地区：[1]中国科学院武汉岩土力学研究所,岩土力学与工程国家重点实验室,武汉430071 [2]中国科学院大学,北京100049 [3]武汉智慧生态建设投资有限公司,武汉430000 [4]武汉市政工程设计研究院有限责任公司,武汉430000 [5]武汉中和工程技术有限公司,武汉430000

出　　处：《工程地质学报》2024年第5期1838-1849,共12页Journal of Engineering Geology

基　　金：国家自然科学基金项目(资助号:41972285,41972293,52178372);中国科学院青年创新促进会项目(资助号:2018363);湖北省杰出青年科学基金项目(资助号:2020CFA103)。

摘　　要：武汉赛车场跑道下伏的深厚软土层给桩基的设计与施工带来不小阻碍,桩基的负摩阻力及其中性点的确定对工程的稳定性具有非常重要的影响。为检验武汉赛车场跑道软土路基的预应力高强度混凝土管桩(PHC)设计的合理性以及为后续桩基改进方案的提供技术支持,选择典型地层开展了堆载作用下桩与桩间土的沉降监测,根据桩与土的相对沉降变化规律研究负摩阻力中性点的时间效应。结果表明,该场地的PHC桩的桩周土沉降约是桩沉降的6倍,具有明显的负摩阻力特性,桩周软弱土的下限深度为13.0 m;随着时间增加,中性点向上移动;中性点深度随时间变化具有三阶段特征,采用指数函数的中性点时间效应预测模型能较好反映中性点初始值、中性点变化规律与速率以及最终稳定值,与规范法比较,预测模型计算的中性点深度具有更高的准确性,由此得到了两个试验场地的中性点稳定值分别为4.43 m与5.72 m。研究还表明三向土工格栅能有效降低桩间土的沉降,也能降低桩-土的差异沉降,使中性点上移,减小负摩阻力,提高桩的承载力。本研究对了解负摩阻力对桩基性能发挥有一定的参考价值。The thick soft soils underlying the Wuhan Motor-racing Circuit have caused substantial challenges to the engineering design and construction.Coping with these issues requires the determination of the negative skin friction force and the neutral point position.To verify the appropriateness of the PHC pile in this site and provide technical guidance for possible future piled foundation enhancement design,long-term monitoring of the settlement of the pile and the surrounding soil was performed.The time dependence of the neutral point was studied according to the settlement of the pile and surrounding soil.The results indicate that the settlement of the PHC pile is 1/6 of that of the surrounding soil,which confirms significant negative skin friction.The layered settlement observation shows that the settlement of the foundation soil is mainly caused by the compression of the soft soils within 13m depth.In the studied sites,the neutral point position is elevated with time on the pile and tends to correspond to a shallower position of the neutral point.In addition,the variation of neutral point position with time consists of three stages and can be described using an exponential model.Such a model predicts better than the construction codes do,and the predicted stable values for the neutral point position in the two test sites are 4.55m and 5.72m,respectively.The current results also confirm the effectiveness of geogrids in reducing the settlement of surrounding soil as well as the differential settlement.Besides,geogrids lead to an elevated neutral point position and reduced negative skin friction.This paper is helpful in understanding how negative skin friction affects the performance of the piled foundation.

关 键 词：软土路基 PHC桩 沉降 负摩阻力 中性点 时间效应 

分 类 号：TU447[建筑科学—岩土工程]