液化场地桩基桥梁抗震设计方法研究

Pile foundations have suffered extensive damage in liquefiable and laterally spreading soil during earthquakes around the world. China is an earthquake-prone country, and a large number of bridges were built in high seismic intensity coastal area with a great quantity of liquefiable fields. So the liquefaction effects on earthquake safety of bridges cannot be ignored. Although there are extensive previous researches on soil-pile-interaction in liquefiable fields around the world, the achievements are not enough to support the seismic design of bridges located in liquefiable fields. The objective of this project is to reveal the damage mechanism of bridge piles in liquefiable site, and to establish the seismic design method for bridges founded on piles in liquefiable field, taking in account the effects of liquefiable and laterally spreading soil. The main researches contain:1) The effect of liquefied and lateral spreading ground on the seismic responses of pile foundation and superstructure of bridges will be analyzed, then the characteristics of seismic response of bridges founded on piles in liquefiable field will be summarized; 2) A shaking table test of piles-pier models in liquefiable soil will be carried out, based which the damage mechanism of pile foundations will be investigated, and the theoretical simulation model will be verified; 3) The problem of the simplified calculation and combination method of soil-pile inertial interaction and geometric interaction in liquefiable site will be solved, then a simplified method for seismic response analysis of bridges founded on piles in liquefiable site will be proposed; 4) A Pushover analysis of pile-pier system in liquefiable site will be carried out, then damage mechanism of pile foundations will be investigated, and lateral deformation capacity of pile foundation will be calculated, finally seismic check targets of bridges founded on piles in liquefiable site will be proposed.

土体液化导致的桩基桥梁地震震害非常常见。我国地震多发，而桥梁众多的沿海地区地震烈度高，又存在大量可液化地带，砂土液化对桥梁抗震安全性的影响不容忽视。国内外对液化场地中桩-土相互作用已经进行了大量的研究，但对于桥梁的抗震设计，研究成果还远远不够。本项目的目标是考虑液化产生的地面大变形影响，揭示液化场地桩基桥梁的地震破坏机理，并建立抗震设计方法。主要研究内容有：1) 考虑液化大变形，分析液化对桩基、桥梁上部结构地震反应的影响，总结液化场地桩基桥梁的地震反应特性； 2）考虑液化大变形，进行液化场地桩基桥梁单墩模型振动台试验，研究桩基地震破坏机理并验证理论计算模型；3）解决液化场地桩土惯性相互作用和几何相互作用的简化计算及组合方法，建立液化场地桩基桥梁地震反应的简化分析方法；4）进行液化场地桩基桥墩系统Pushover分析，研究地震破坏机理以及地震变形能力，提出液化场地桩基桥梁的抗震验算指标。

近数十年来，由于地震引发的砂土液化所导致的桥梁结构损毁的震害在全球范围内屡有报道，而我国桥梁众多，且多数处于地震烈度较高的沿江沿海地区，存在大量可液化地带，故而砂土液化对桥梁抗震安全性的影响不容忽视。国内外学者已经对液化场地中土体液化机理和桩-土相互作用进行了大量的研究，但对于桥梁结构的抗震设计，研究成果还远远不够。本项目的目标是考虑液化产生的地面大变形影响，揭示液化场地桩基桥梁的地震破坏机理，并建立抗震设计方法。围绕这样的研究目标，课题组采用理论分析结合试验研究的方法开展了如下研究：首先，提出了可考虑液化土层局部剪切变形特性的二维场地、三维结构的多尺度有限元模型，并采用国外离心机试验验证了数值模型。在此基础上，进行了液化场地桩基桥梁地震反应的参数敏感性分析。根据分析结果，选取高敏感性参数，进行了振动台试验的设计，通过试验结果，揭示了液化场地桩基桥梁的地震破坏机理。而后，建立了能够代表液化场地-桩基桥梁结构的单墩简化模型，并进行大量的数值参数分析，总结地震反应规律，并提出了简化的抗震设计方法。最后，依托实际工程，建立了场地-全桥的有限元模型，研究了桥梁结构各部件在液化场地的地震反应特性，数值结果与实际震害相吻合。本项目的研究成果可为我国桥梁抗震设计规范的改进提供有力的支持。