考虑持时效应的地震动强度指标与场地液化触发阈值研究

Seismic liquefaction of sandy soils and its evaluation are key themes in geotechnical earthquake engineering. The timing of liquefaction has been a missing dimension in liquefaction hazard evaluation, which allows the level of loading imposed by an earthquake to be divided into pre-triggering and post-triggering portions. The use of timing information will improve both the triggering and consequence prediction of soil liquefaction, and has tremendous value in both scientific and engineering perspectives. The present project will focus on the mechanism of duration effect of strong ground motion and its cumulative damaging effect on liquefiable soils, and carry out theoretical and numerical analyses, multi-scale experimental studies and field case history investigations, to develop the composite, liquefaction-specific, evolutionary intensity measure of ground motion for liquefaction evaluation by theoretical study, to reveal the liquefaction triggering thresholds of evolutionary intensity measures of ground motion based on soil element test and establish the correlation between the thresholds and soil parameters, to carry out site response analysis for predicting the depth-variation patterns of intensity measures of ground motion by numerical simulation and obtain key response observations and validate the findings obtained at soil element scale by performing centrifuge model tests, to establish new type of field case histories containing the timing information of liquefaction by conducting field investigations on earthquake liquefaction sites, for checking the feasibility of the proposed timing procedure based on liquefaction triggering thresholds of evolutionary intensity measures of ground motion. The present study will provide the basis for the refined evaluation of liquefaction hazards and the development of performance-based liquefaction mitigation design in engineering practices.

场地液化灾变评价是岩土地震工程领域的核心课题之一，研究地震动作用过程中的场地液化触发时间，据此将地震动强度指标分为液化前、后两部分，有助于提高场地液化触发判别和液化后大变形评价的定量准确性，具有重要的科学意义和工程价值。本项目拟围绕地震动持时效应及其对场地土体累积损伤机制这一关键科学问题，开展理论与数值分析、多尺度试验及地震液化实例研究，包括：通过理论分析，发展考虑持时效应的地震动时变强度指标表征方法；开展单元体试验，揭示砂土液化触发的地震动强度指标阈值，建立触发阈值与土体参数的表征关系；开展场地地震响应的数值模拟和离心模拟试验，揭示地震动强度指标的场地时空分布特征，验证单元体尺度研究认识的合理性；开展地震液化实例研究，构建包含液化触发时间信息的新型场地液化实例数据库，检验基于触发阈值的场地液化时间确定方法的适用性，为精细化的场地液化灾变评价和基于性能的抗液化设计提供科学依据。

场地液化灾变评价是岩土地震工程领域的核心课题之一，地震引起场地液化触发的时间与地震动作用时间并不一致，据此将地震动强度指标分为液化前、后两部分，有助于提高场地液化触发判别和液化后大变形评价的定量准确性，具有重要的科学意义和工程价值。本项目围绕地震动持时效应及其对场地土体累积损伤机制这一关键科学问题，开展理论与单元体材料力学研究，物理模拟与数值分析，以及实际场地地震液化案例研究，取得了以下成果：.（1）通过理论分析发展考虑持时效应的地震动时变强度指标表征方法，揭示砂土液化触发的地震动强度指标阈值，建立触发阈值与土体参数的表征关系。提出基于应力的地震动强度指标（如峰值加速度PGA或动剪应力比CSR）的时变表达式，发展考虑持时效应的地震动时变强度指标（包括Ia、CAV、耗散能等）；在单元体尺度研究地震动时变强度指标随荷载幅值、频谱和振次（时间）的变化规律，及其与饱和砂土超静孔压和残余应变水平的关联性，比较不同地震动强度指标对砂土液化灾变过程的表征性能；揭示地震动强度指标的液化触发阈值及其与土体参数（如剪切波速、静力触探端阻或标准贯入锤击数）的相关关系；.（2）开展场地地震响应的数值模拟和离心模拟试验，揭示地震动强度指标的场地时空分布特征，验证单元体尺度研究认识的合理性。通过数值模拟研究地震动传播规律，揭示各类地震动强度指标在场地上的时间（液化前后）和空间（深度方向）分布特征，针对液化触发判别提出与各类地震动强度指标对应的深度折减因子；开展砂土地震液化模型试验，并联合监测模型土体的剪切波速和静力触探参数，在模型尺度揭示地震动强度指标的场地时空分布特征，检验地震动时变强度指标表征场地液化灾变过程的合理性与单元体尺度所揭示的触发阈值准确性；.（3）开展地震液化实例研究，构建包含液化触发时间信息的新型场地液化实例数据库，检验基于触发阈值的场地液化时间确定方法的适用性，为精细化的场地液化灾变评价和基于性能的抗液化设计提供科学依据。以实际场地和地震动为对象，建立基于地震动强度指标触发阈值的场地液化时间确定方法；开展典型强震液化事件的原位调查研究，构建包含地震动强度指标触发阈值和液化触发时间信息的新型场地液化实例数据库，识别场液化触发前、后不同的灾变阶段，为精细化界定基于场地液化实例数据库的“地震动强度指标-原位测试参数”砂土抗液化强度边界线提供依据。