堆载作用下深厚软土塑流与高铁桥梁桩基相互作用机理及计算方法研究

With the rapid development of traffic construction, building and industrial activity, the permanent surcharge or the temporary surcharge is laid frequently nearby the high-speed railway line. The surcharge on deep soft soil stratum would result in soil plastic flow, and the additional displacement of pile foundation occurs consequently. As a result, the work performance of bridge pile foundation would be severely deteriorated. It affects seriously the track regularity of high-speed railway and even threatens its running safety. While the systematical research works on the interaction mechanism between pile foundation and surcharge-deduced soft soil plastic flow and its design calculation method are rare. Taking the pile foundation of high-speed railway bridge as prototype, a series of large-scale pile foundation model tests and numerical simulation will be performed to investigate the interaction mechanism between pile foundation and surcharge-deduced soft soil plastic flow in this project, the plastic flow of soft soil, the displacement of soil around the pile, the lateral stress on the pile, the internal force and deformation of the pile can be observed and monitored continuously. Then the plastic flow mechanism of soft soil around the pile can be derived. Considering loading history, a method for the progressive development of lateral displacement of soil around the pile until plastic flow will be presented, which is based on the large strain rheological analysis and seepage consolidation theory. Moreover，the interaction mechanism of lateral movement of soil-pile will be examined at each stage, with the state characteristic and quantification of demarcation index. The rule of multiple factors which influence the interaction mechanism such as design parameters of pile foundation, soil conditions and the form of surcharge will be explored. A universal equation expressing the additional horizontal stress at pile shaft for whole loading levels will be established. Furthermore, a theoretical model and algorithm for analyzing the active-passive combined piles subjected to adjacent surcharge will be proposed, which takes the nonlinear characteristic of soil resistance into consideration. Eventually, all the methods can be complied as a software to analysis the internal force and deformation of the active-passive combined piles subjected to adjacent surcharge. The findings of this project will be expected to supply the theoretical knowledge for improving the design method of bridge pile foundation, as well as developing a control criterion of adjacent surcharge to ensure the high-speed railway bridge operation with high quality.

随着交通建设、建筑与工业活动的迅速发展，高铁沿线永久和临时堆载时有发生。深厚软土地区堆载引发的土体塑性流动极易诱发桥梁桩基位移，严重影响线路平顺度，劣化其工作性状，威胁行车安全，但目前缺乏系统研究和分析方法。项目针对高速铁路桥梁桩基，开展邻近堆载与承载桩基相互作用的大比尺模型试验和数值模拟，全过程观测堆载作用下软土塑流、桩周土位移、桩侧应力、桩身内力和变形的发展规律；揭示软土塑流机理，基于大应变渗透固结流变分析，提出桩周土位移随堆载历程渐进性发展直至塑性流动的全过程分析方法；探明侧移土体-桩相互作用机理，明确其各阶段状态特征及分界指标，分析桩基设计参数、土层条件、堆载形式等因素对桩土相互作用的影响规律与阈值，建立桩侧附加水平力的全过程描述方程；构建邻近堆载作用下主被动联合受力桩的理论模型与求解算法，研发计算分析软件。研究成果将为完善高铁桥梁桩基设计方法和出台邻近堆载控制标准提供依据。

随着我国交通建设的迅猛发展，路网密集化、空间化使得高铁沿线邻近长期或临时堆载时有发生。对于深厚软土区高铁桥梁桩基而言，邻近堆载可能引发软土侧向塑流，造成桩基横向偏移，导致墩顶位移过大，影响运营品质，甚至威胁行车安全。然而受限于软土塑流的非线性变形行为及桩基的复杂受力模式，深厚软土塑流与承载桩基的相互作用机理及其计算方法仍缺乏系统研究。对此，本项目开展了系列研究，获得主要研究成果如下：（1）基于一维固结-蠕变试验，对一维Koppejan模型进行了三维扩展，基于该模型揭示了堆载条件下软土侧向变形特性；（2）开展了堆载-桩基现场原型试验，获得了不同堆载工况下桩周土位移、桩侧应力、桩身内力和变形的发展规律；（3）通过数值分析研究了侧移软土-桩基时效性相互作用过程，阐明了桩间土拱效应的弱化机制及软土塑流机理，揭示了侧移软土-桩基时效性相互作用机理；（4）采用桩-土界面黏着力ca值和外摩擦角φa值表征界面摩擦特性，推导了考虑桩-土界面摩擦影响的桩侧被动荷载计算表达式；（5）考虑软土绕流大变形特征，提出了侧移软土-桩基相互作用耦合欧拉-拉格朗日（CEL）数值建模方法，揭示了软土绕流对桩身被动荷载的影响机理；（6）针对桩侧土体处于弹性、弹塑性和极限塑流不同状态，建立了桩侧被动荷载的全过程统一描述方法；（7）引入典型黏土桩侧抗力非线性模型（p-y曲线），考虑主动荷载及“P-Δ”效应，构建了主-被动联合受力桩响应全过程计算模型，研发了计算分析软件；（8）依托典型工程案例，提出了“卸载+高压旋喷桩加固”的桥墩横移整治措施，对比讨论了微型桩及应力释放孔措施对桩基偏移的预防效果。项目执行过程中，发表学术论文17篇，其中SCI和EI检索15篇，软件著作权2项。上述研究成果提高了对邻近堆载作用下桥梁桩基工作性状的认识水平，完善了高速铁路桥梁桩基设计计算方法，能为制定深厚软土地区高铁桥梁邻近堆载的控制标准提供参考依据。