开口管桩循环打入过程及竖向承载特性大比尺模型试验研究  

Large-scale model experimental study on cyclic penetration process and vertical bearing characteristics of open-ended pipe piles

作　　者：朱怀龙 朱碧堂 罗如平 徐长节[1,2,4] ZHU Huai-long;ZHU Bi-tang;LUO Ru-ping;XU Chang-jie(State Key Laboratory of Performance Monitoring Protecting of Rail Transit Infrastructure,East China Jiaotong University,Nanchang,Jiangxi 330013,China;Engineering Research&Development Center for Underground Technology of Jiangxi Province,Nanchang,Jiangxi 330013,China;Jiangxi Vocational and Technical College of Communications,Nanchang,Jiangxi 330013,China;Research Center of Coastal and Urban Geotechnical Engineering,Zhejiang University,Hangzhou,Zhejiang 310058,China)

机构地区：[1]华东交通大学轨道交通基础设施性能监测与保障国家重点实验室,江西南昌330013 [2]江西省地下空间技术开发工程研究中心,江西南昌330013 [3]江西交通职业技术学院,江西南昌330013 [4]浙江大学滨海和城市岩土工程研究中心,浙江杭州310058

出　　处：《岩土力学》2024年第11期3173-3184,共12页Rock and Soil Mechanics

基　　金：国家自然科学基金项目(No.52020105003,No.52208343);江西教育厅科技项目(No.GJJ2205202)。

摘　　要：深入认识桩打入过程的桩-土作用机制对准确计算打入桩的竖向承载力十分重要。为探究砂土中开口管桩在循环打入时桩-土作用机制及打桩结束后的竖向承载特性,开展了直径为0.273 m的开口钢管桩静压循环打入过程的大比例尺(1:10)模型试验,砂土的相对密实度约为40%,通过采用光纤光栅(fiber Bragg grating,简称FBG)应变传感器和薄膜压力传感器等先进监测手段,研究循环打桩过程中土塞高度、桩身应变、轴力和侧摩阻力以及桩-土界面应力变化规律。打桩结束后,进行了休止时间分别为10d和30d竖向受压静载试验。随后,将基于静力触探试验CPT的ICP-05法和UWA-05法预测桩竖向承载力与静载试验测量的承载力进行对比分析。结果表明:开口管桩在静压循环打入过程中土塞效应逐渐增强,贯入结束后土塞呈部分闭塞状态;随着贯入深度的增加,靠近桩尖的应变会出现“反点”,即由贯入最后阶段的压应变转为静止稳定阶段的拉应变,而桩尖处的应变在两个阶段均为拉应变;桩身径向应力在桩尖处最大,随着h/R(h为传感器距桩尖的高度,R为桩半径)的增加而逐渐减小,具有明显的h/R效应;休止时间为10 d和30 d的极限承载力分别为289 kN和323 kN,承载力提高约12%,桩承载力具有明显的时间效应;采用ICP-05法和UWA-05法预测桩尖附近的侧摩阻力被低估,而桩尖以上侧摩阻力与实测值吻合较好,ICP-05法和UWA-05法预测桩基承载力偏保守,UWA-05法更接近实测值。It is extremely important to understand the mechanism of pile-soil interaction during pile installation for accurately predicting its bearing capacity.This paper presents a large-scale(1:10)model test to investigate this interaction specifically for open-ended pile penetrating sandy soil.The study focuses on pile with a diameter of 0.273 m penetrating sandy soil having a relative density of approximately 40%.Advanced monitoring techniques,including fibre Bragg grating(FBG)strain sensors and thin-film pressure sensors,were employed to meticulously analyze changes in soil plug height,strain,axial force,shaft resistance,and pile-soil interfacial stress throughout the cyclic penetration process.Following pile installation,vertical compressive static load tests were conducted with intervals of 10 and 30 days,respectively,to assess the long-term performance of the piles.Subsequently,the ICP-05 method and UWA-05 method,which are based on CPT to predict the vertical bearing capacity of piles,were compared with the bearing capacity measured by static load test.The results indicate the following:Firstly,the soil plug effect of open-ended pipe piles gradually increases during cyclic penetration,and the soil plug is partially occluded at the end of penetration.Secondly,as the depth of penetration increases,an“inverse point”of strain near the pile tip emerges.Specifically,the compressive strain at the final stage of penetration changes to a tensile strain during static stabilization,while the strain at the pile tip remains tensile at both stages.Thirdly,the radial stress of the pile body peaks at the pile tip and gradually tapers off as the h/R(h is the height from the sensor to the pile tip,R is the radius of the pile)ratio increases,indicating a significant h/R effect.Fourthly,the bearing capacity of the pile increased by approximately 12%,from 289 kN after 10 days to 323 kN after 30 days,demonstrating a notable time effect.Finally,both the ICP-05 and UWA-05 methods underestimate the shaft resistance near the pile tip,w

关 键 词：开口管桩 静压循环打入 光纤光栅应变传感器 土塞效应 竖向承载力 

分 类 号：TU473[建筑科学—结构工程]