基于海域软土孔压和残余应变模型试验的饱和土场地时域积分方法研究

At present, experimental and theoretical study on the dynamic characteristics of soil in sea area has been seriously lagged behind the soil in land area. Existed seismic response analysis methods is difficult to describe the effect of pore water pressure and the residual strain of saturated soft soil, so it is difficult to evaluate its effect on the parameters of ground motion. Our research will extend a constitutive relation which derived from the combination of the Remanent Strain Potential Model and the Dynamic Skeleton Curve to the form of considering the effect of pore water pressure. Through resonant column, dynamic triaxial and hollow torsional shear test, pore pressure model and residual strain effect of typical saturated soft soil in sea area are studied, the empirical correlation of pore water pressure development and key parameters in residual strain potential model are determined. After that, using the extended soil constitutive relations, combined with time domain step by step numerical integral method and artificial transmitting boundary, a direct-domain integral method for seismic response analysis is proposed. It can describe the effect of pore water pressure and the residual strain of saturated marine soft soil simultaneously. Finally, this method is used to study the influence of the soft soil on the ground motion parameters. The study of this project will provide experimental and theoretical basis for the treatment of common saturated soft soil in sea area, which has important theoretical significance and engineering application prospect.

目前，海域土体动力特性的试验与理论研究相对于陆域已经严重滞后，已有的场地地震反应分析方法难以考虑海域饱和软土孔隙水压的影响和明显的残余应变效应，难以评价其对地震动参数的影响。本项目将一种已得到应用的结合土体残余应变模型及动态骨架曲线的本构关系推广至可以考虑孔隙水压的情形，通过室内共振柱、动三轴、空心扭剪试验研究典型海域饱和软土孔压增长模式和残余应变效应，确定符合其动力特性的孔压增长经验关系以及残余应变势模型中的关键参数。随后，将推广后的本构关系与时域逐步积分方法和多次透射人工边界条件结合，给出适用于海域饱和软土且能同时考虑孔压及残余应变效应的土层时域积分方法。最后利用该方法研究海域软土对地震动参数的影响规律。本项目研究将为海域工程常见的软土层的处理提供试验依据与理论基础，具有重要的理论意义及工程应用价值。

目前，海域土体动力特性的试验与理论研究相对于陆域已显滞后，已有的场地地震反应分析方法难以考虑海域饱和软土孔隙水压的影响和明显的残余应变效应，难以评价其对地震动参数的影响。本项目调研和整理了海域软土动力特性相关试验与理论研究成果；基于室内土体动三轴试验给出了土体结构性、围压、固结比等试验参数对土体动力特性的影响规律；给出了循环荷载作用下海域典型饱和软土孔隙水压增长的经验关系式及相应系数、残余应变模型的关键参数；针对海域饱和软黏土、饱和砂土分别实现了考虑孔压增长模式的土体动态骨架曲线本构模型的修正；在修正的本构模型基础上发展了与时域逐步积分格式和多次透射人工边界条件相结合的一维时域土层地震反应分析方法并验证了方法的合理性与可靠性；发展了可同时考虑孔压与残余应变的土体时域地震反应分析方法；基于大量实际海域钻孔给出了海域典型软土对地震动参数的影响规律。研究表明，项目发展的时域地震反应分析方法合理可靠，能同时模拟孔压增长与土体强非线性；近海域普遍存在的厚软表层土将导致地表反应谱出现“矮胖”现象，剥离与未剥离表层软土情况下地表峰值加速度相对偏差可达到143%，特征周期相对偏差可达83%，且相对偏差主要出现在中、强地震动输入情形。本项目研究将为海域工程常见的软土层的处理提供试验依据与理论基础，具有重要的理论意义及工程应用价值。