地震历史对砂土抗液化强度剪切波速表征关系的影响规律研究

Seismic liquefaction of sandy soils and its evaluation is key theme in geotechnical earthquake engineering. The development of physically meaningful and field applicable correlation between liquefaction resistance and shear wave velocity become research hotspot in recent years. For a given site, the seismic history (i.e., preshaking by previous earthquakes) is the dominant factor that influences the liquefaction potential of the critical layer soil. The study on the quantitative effect of seismic history on CRR-Vs correlation of sandy soils will provide scientific and engineering merits for improving the reliability of liquefaction evaluation in the field. The present project will focus on the mechanism of seismic history effect on soil microstructure and stress state, and carry out multi-scale experimental studies including dynamic soil element test, dynamic geotechnical centrifuge model test and field investigation with shear wave velocity measurement, to reproduce seismic history with different amplitudes and frequencies, and reveal its effects on the changes of soil microstructure and stress state; to construct the evaluating index based on earthquake intensity measures to quantify the variations of the correlation between liquefaction resistance and shear wave velocity, and therefore reveal the seismic history dependency of CRR-Vs correlation; to collect liquefaction case histories from typical big earthquakes, and develop a new type of (CSR, Vs) database containing seismic history information, which will provide the basis for evaluating the feasibility of proposed CRR-Vs correlation in the field. The present study will provide the basis for the development of liquefaction evaluation method towards the seismic history dependent one, and help to improve its reliability in engineering practices.

场地液化判别是岩土地震工程领域的核心课题之一，基于剪切波速指标建立既有物理意义又能反映原位土体抗液化强度的表征关系是近年来的研究热点。先期地震历史对场地抗液化性能有重要影响。研究地震历史对砂土抗液化强度剪切波速表征关系（即CRR-Vs相关关系）的定量影响，对提高剪切波速判别方法的可靠性有重要科学意义和工程价值。本项目拟围绕地震历史对场地土体结构性和应力状态影响机理这一关键科学问题，开展监测剪切波速的多尺度试验研究，在室内单元体和离心模型试验中重现不同幅频特性的先期地震历史，揭示其对场地土体结构性和应力状态的影响机理；提出基于地震动参数的地震历史评价指标，定量分析剪切波速表征关系的地震历史相关性和变化趋势；通过震害调查，构建包含地震历史信息的新型地震液化实例数据库，检验剪切波速表征关系在现场判别中的适用性，为推动当前场地液化判别向考虑地震历史的可靠评价发展提供科学依据。

场地地震液化判别是岩土地震工程领域的核心课题。近年来震害实例研究表明，不同地质沉积年代和地震历史对场地土体的抗液化能力影响显著。现有方法假设地震事件独立，场地土体抗液化强度不随地震历史改变，将对一定时空条件下场地液化判别带来误差。.本项目围绕地震历史对砂土抗液化强度剪切波速表征关系的影响规律，揭示地震历史对场地土体结构性和应力状态的影响机制，定量评价地震历史对砂土抗液化强度及剪切波速的影响规律，构建包含地震历史信息的新型场地液化实例数据库，检验CRR-Vs表征关系在实际场地的适用性与可靠性。通过多尺度剪切波速的多尺度试验与观测，在室内单元体和超重力模型试验重现地震事件来定量分析地震历史对砂土抗液化强度与剪切波速的协同影响。主要研究成果为：1）不同地震动强度将会显著增大或者弱化土体结构性从而影响土体的抗液化能力，并揭示了砂土结构性随地震历史演化规律；2）开展了系列时间效应和不同超固结比单元体试验，验证了CRR-Vs1表征模型的本征性；3）基于现场震害调查观测到地震历史对场地刚度演化的时间效应，构建了考虑时间效应的新型液化震害实例数据库；4）基于理论分析和实验研究建立了地震损伤与考虑时间效应的震后刚度恢复计算公式，并得到了超重力模型试验的验证，该公式为定量修正震后原位波速测试指标提供了科学依据。.本项目揭示了地震历史对土体结构性和抗液化强度的影响规律，验证了基于剪切波速抗液化模型的本证性，对提高场地地震液化判别可靠性有重要科学意义和工程价值。研究成果共发表期刊论文11篇（SCI检索8篇），国际会议论文4篇；授权国家发明专利5项、国际发明专利1项；获得省部级科技进步一等奖2项；培养研究生毕业8名、本科生毕业1名；负责人获浙江省杰出青年基金1项。