大轴重列车荷载作用下桥梁摩擦桩基力学响应与变形机理研究

With the increase of train axle load,traction tones and traffic density of the heavy haul railway in China, the dynamic responses of bridge foundation have significantly increased, particularly, some obvious dynamic accumulated settlement has happened in friction piles foundation from field tests. The methods of field tests, laboratory experiments, theoretical analysis and numeric calculation will be adopted to systematically study the main contents as follows: (1) investigation and analysis of work status and disease characteristics of the heavy haul railway bridge pile foundation; (2)study on the law of the dynamic responses of the system of bridge-pier-friction piles-foundation under heavy-axle train loading; (3) experimental study on the static and dynamic characteristics of piles-soil interface; (4) the large-scale model tests study on the deformation characteristics and fracture mechanism of of the friction pile foundation subjected to heavy-axle train loading; (5) study on the consolidation -creep settlement of the heavy haul railway bridge pile foundation; (6) numerical simulation of the heavy haul railway bridge pile foundation and prediction of the accumulated deformation. Based on these systematic studies, the mechanical response and deformation mechanism of the heavy haul railway bridge pile foundation will be brought to light, and the method of forecasting settlement of the bridge foundation under heavy-axle train loading will be proposed. These achievements can provide scientific basis for the assessment of service state of pile foundation, and give technical advice on the reinforcement design of pile foundation. Also, the study can provide significant references for the revision of relevant existing maintenance specification.

随着我国重载铁路列车轴重、牵引质量的不断提高以及行车密度的增加，观测表明桥梁地基基础的动力响应随之明显加大，特别是摩擦型桩基，不少发生了明显的动力累积沉降。本项目拟采用现场测试、室内试验、理论分析和数值计算相结合的方法，开展如下相关研究：⑴我国既有重载铁路桥梁摩擦型桩基工作现状和病害特征调查分析；⑵大轴重列车作用下梁-桥墩-摩擦型桩基-地基体系的动力响应规律研究；⑶摩擦型桩桩-土接触面静动力特性试验研究；⑷大轴重列车作用下摩擦桩基变形特性和破坏机理大比例尺模型试验研究；⑸重载铁路桥梁摩擦桩基的固结-蠕变沉降研究；⑹大轴重列车作用下桥梁桩基数值仿真及累积变形预测研究。通过系统深入研究，揭示大轴重列车作用下桥梁摩擦型桩基力学响应特性与变形机理，建立大轴重重载铁路桥梁桩基沉降变形预测评估方法。研究成果可为重载铁路桥梁桩基服役状态评估、加固强化设计和相关养护维修规范的修订提供科学依据与技术基础。

随着我国重载铁路列车轴重、牵引质量的不断提高以及行车密度的增加，桥梁基础的动力响应随之明显加大，特别是摩擦型桩基，可能出现承载不足和动力累积沉降增加的问题。课题组采用现场测试、室内试验、理论分析和数值计算相结合的方法开展了相关研究，主要研究内容和成果如下：. （1）大轴重列车引起的竖向动荷载峰值、幅值近似线性衰减。竖向动荷载峰值随轴重增大而增大。墩顶、墩底的竖向动荷载峰值范围分别为3115~4224kN和2105~3388kN。. （2）墩顶、墩底（桩基）动荷载时程曲线呈现明显的周期性，周期对应列车车长加载周期。列车车长加载频率对动荷载峰值贡献最大。墩顶动荷载放大系数与列车速度的关系式为φ=1+0.0111v。获得了墩顶和桩基顶动荷载谱Q(t)=Qa+0.5Qccos(wt+φ)及其动荷载特征参数值。. （3）大轴重列车荷载作用下产生的桩基沉降小于0.5mm，远小于规范限值50mm。现有列车荷载水平条件下，对桥梁桩身轴力、压缩变形和桩侧摩阻力的大小、分布影响甚小。. （4）提出可考虑凹槽几何参数、槽内土体扰动深度和槽宽修正的粗糙度(R)计算方法，接触面峰值应力比随lgR近似呈线性增长, 砂土的自身切剪强度不是接触面剪切强度的上限。获得了粗糙度、泥皮厚度和法向应力对接触面强度的影响规律。揭示了泥皮弱化接触面抗剪强度机理机理。建立了桩土接触面非线性本构关系，并进行了二次开发，其能更好的模拟分析桩土接触面的力学特性。. （5）建立了大轴重列车荷载作用下桥墩-桩-地基的数值仿真模型，获得了23t~40t轴重下墩底、桩顶动荷载随轴重的变化规律，不同轴重条件下动荷载、动位移沿桩身衰减规律，获得了不同轴重条件墩顶、桩基顶、基桩顶的动荷载峰值与幅值。. （6）采用循环变形图和循环交互图两种评价方法，对轴重23t~40t荷载条件下重载铁路桥梁摩擦桩基的承载变形性状进行了评估，获知桩顶不会产生明显的累积沉降，承载和变形都处于稳定状态，工作状态良好。. 研究成果可为重载铁路桥梁桩基服役状态评估、加固强化设计和相关养护维修规范的修订提供科学依据与技术基础。