软土震陷机理及桩土沉降控制模式

Reducing_settlement pile foundation is designed according to controlling settlement principle and is a style of foundation which consists of cap with enough base capability and groups of friction pile. Reducing_settlement pile foundation has been compiled into Code for design of building foundation in some areas and national code for building pile foundations. It has been confirmed as one style of foundation and put into practice widely. However, whether it can be used in earthquake fortifying areas and how to be used are still problems that haven't been studied deeply. Seismic settlement mechanics of soft soil and controlled-settlement mode between pile and soil are two key scientific themes. Some research should be done as follows in the project according to such scientific themes: 1. Study on seismic settlement mechanics of soft soil and evaluation. 2. Seismic response analysis of sigle pile foundation and seismic settlement evaluation of soft soil. 3. Study on interaction mechanics between reducing_settlement pile foundation and soil during earthquakes. 4. The effect of seismic settlement to the ultimate capacity and settlement of reducing_settlement pile foundation. In this project, theoretic analysis of pile-soil dynamic interaction is used, geotechnical centrifuge model test on shaking table is established，and numerical feedback analysis is used. It is expected to explore interactional mechanics between reducing_settlement pile foundation and soil during earthquakes, Safety performance of reducing_settlement pile foundation is assessed in deformation and capacity, design method is supplied for the engineering practice of reducing settlement pile foundation in earthquake fortifying areas.

减沉桩基是指按控制沉降的原则进行设计并由具有足够地基承载力的承台和较大桩距的摩擦桩群共同组成的基础形式。减沉桩基在我国已纳入部分地区地基基础设计规范和国家桩基础设计规范，作为一种基础形式已得到确认并已有广泛的工程应用。然而，在抗震设防软土地区减沉桩基能否应用及如何应用还是一个未能深入研究的问题，而软土震陷机理及其桩土沉降控制模式是其中的两个关键科学问题。本项目拟针对上述科学问题开展以下研究：1. 软土震陷机理研究及震陷量计算；2.单桩基础动力响应特性分析及土体震陷量计算；3. 震陷条件下减沉桩基与土相互作用机理研究；4. 软土震陷对减沉桩基沉降和承载力的影响。拟采用桩-土动力相互作用的理论分析，建立土工离心机振动台模型试验，并进行数值反馈仿真，探讨软土震陷机理及震陷条件下减沉桩基与土的相互作用的机理，评价减沉桩基础的抗震安全性能，为抗震设防软土地区减沉桩基础的应用提供理论基础。

本项目基于减沉桩基础在静力及地震荷载作用下的工作机理和工程应用问题开展了相关的理论计算、案例分析和试验研究，探讨了其场地适用评价标准及相关设计方法，并研究了在地震荷载作用下其抗震性能，为减沉桩基础在地震地区中的应用提供参考。.（1）基于理论研究及案例统计分析提出了减沉桩基础在不同场地下的适用标准，并根据桩-土-筏相互作用理论提出了考虑土体非线性的共同作用的实用分析方法。.（2）采用三维有限元模型确定了减沉桩基础极限承载力取值标准，并探讨了不同工况条件下基础整体安全系数与沉降之间的内在关系。.（3）基于二维Terzaghi-Rendulic固结理论，提出了考虑固结效应的减沉桩基础沉降简化分析方法，并通过与理论和实际工程案例进行对比，验证计算模型合理性及适用性。.（4）采用离心机-振动台-剪切箱试验系统进行软土地基减沉桩基础-结构体系动力离心模型试验，研究了饱和软土地基中不同桩距和桩筏连接形式下摩擦桩基础地震响应规律，揭示软土震陷条件下减沉桩基础的变形控制机理。.（5）结合工程实际建立了上海地区某12层框架结构的地基-基础-上部结构相互作用三维模型，研究了在地震荷载作用下基础连接方式对桩基内力及上部结构位移的影响，为工程设计提供参考。