【作者】 陈龙伟；

【导师】 袁晓铭；

【作者基本信息】 中国地震局工程力学研究所 ， 岩土工程， 2011， 博士

【摘要】 宏观震害经验表明,地震中软弱场地、土体非线性以及可液化土层等对上部工程结构、地基基础与地下工程结构物的破坏影响很大。而地震荷载对工程结构的影响主要从惯性力和变形两个方面考虑。对地上建筑结构而言,惯性力起控制作用,土体非线性对惯性力的影响在抗震设计中由反应谱体现,此部分由地震动的加速度反应谱控制：对于地基基础和地下结构而言,土体变形作用超过了惯性力的作用,此部分由地震动中位移响应控制。土体弱化主要表现在三个方面,一是场地本身很软；二是强震下土体强非线性引起的土体软化：三是地震下土层液化导致的土体软化。这三个方面对地震动加速度反应谱和土层变形均有很大影响。这类问题实际上是不同类别的场地上地震波引起场地土体弱化,弱化土层又引起地表地震波的变化,属于典型的地震波.土层弱化动力相互作用。这种相互作用研究的关键是地震波与弱化土层特征关联性的理解及相互作用规律的掌握,但目前国内外对其机理和规律还没有形成完整的认识,土体弱化与地震动之间关联性的量化关系研究尚少,理论基础较为缺乏。本论文将土体弱化(含液化)与地震动的关系进行统一考虑,利用波动理论和动力学原理,以土体弱化和地震动关联性理论及相互作用规律为主题,提出简化理论模型并给出频域和时域解答,分析讨论各参数影响,利用理论解的优势,初步提炼土体弱化和地震动关联性的量化关系及相互作用规律,主要工作和成果如下：1.利用大型振动台试验手段研究饱和砂土液化对地表运动的影响,了解场地液化地表运动规律及孔压升高地表运动变化过程；掌握土层在动荷载作用下弱化损伤条件地面运动和变形的发展过程,提出土体弱化下土表运动变化特征。2.分析现有孔压增长模型,提出适于水平土层应力条件的修正的孔压增量计算模型,采用逐波循环(Cycle-by-Cycle)迭代法逐循环累积计算孔压比发展进程,给出随机荷载下孔压比增长计算方法,并利用振动台试验结果验证修正模型的合理性。3.建立水平工程场地土体弱化下地面运动的简化计算模型,根据稳态波频域解推导地表运动(加速度和位移)频域响应的理论解答,通过参数分析讨论土体弱化对地表运动响应的影响因素及规律,指出土体弱化过程和液化后地表响应特征。4.采用土体弱化地面运动变化过程的简化计算模型,利用Fourier正(逆)变换方法给出动荷载作用下地表运动过程描述的时域解析解答.通过数值计算,分析土体弱化对地表运动时程的影响规律和特征.并结合大型振动台试验结果验证时域解答的合理性。5.通过简化模型解析解分析提取出土体弱化特征量以及土体弱化引起地震波谱变化的特征量,提出土体弱化对地震动影响的参数指标,建立土体弱化过程与地震波特征的关联性及相互作用规律,得到土体弱化过程与地震波特征的关联性和相互作用规律定性方面的初步认识。更多还原

【Abstract】 Macro earthquake-investigation experiences demonstrate that the effects of soft sites, subsoil nonlinearity and liquefiable layers on the damage to superstructures, foundations and underground structures are tremendous. The effects of seismic loading on engineering structures mainly take the forms of inertia forces and soil deformation. To superstructures, the influence of inertia forces is predominant. The design response spectra have incorporated subsoil nonlinearity and are controlled by ground acceleration response spectra. To foundations and underground structures, however, subsoil-deformation act which is controlled by ground displacement response surpasses inertia forces.Subsoil degradation principally represents in three aspects, i.e., (1) natural soft sites; (2) soil nonlinearity induced by subsoil degradation under strong earthquakes; (3) subsoil degradation caused by liquefaction. The three aspects specially influence acceleration response spectra and soil deformation. Actually, seismic waves result in subsoil degradation; meanwhile, subsoil degradation conversely alters seismic waves. It is a typical seismic waves-subsoil degradation interaction problem. The crucial point for the interaction is to comprehend the correlation and interaction rules of seismic waves and subsoil degradation. Nevertheless, currently the mechanism and interaction rules have hardly been wholly acquainted. A quantitative relationship between soil degradation and ground motions has not yet been manifested and theoretical explanations are quite limited.In the thesis, subsoil degradation including liquefaction and ground motions are simultaneously considered. Taking correlation theories and interaction rules as a theme, simplified theoretical models and relevant solutions both in frequency domain and in time domain are proposed employing wave propagation theories and dynamic principles. The influencing parameters are analyzed individually. Preliminary quantitative correlations and interaction rules of subsoil degradation and ground motions are illustrated. The main salient points and achievements obtained can be outlined:1. By means of large shaking table tests, the influence of soil liquefaction on ground motions has been investigated along with ground motions characteristics with increasing excess pore-water pressure. Ground motions and deformation progress resulted from subsoil degradation and deterioration under dynamic loadings are described and characteristics of ground motions are presented.2. Analyzing the existing pore-water pressure buildup models, a modified pore-water pressure incremental model for horizontal strata and the relevant procedure to calculate pore-water pressure process are proposed. Using the Cycle-by-Cycle method, pore-water pressure buildup process under irregular seismic loadings can be calculated. Eventually, the modified model is testified by the large shaking table testing results.3. Simplified models, which consider subsoil degradation, are established for simulating horizontal engineering sites. By steady-state wave solutions in frequency domain the theoretical solutions for ground motions, i.e., displacement and acceleration, under harmonic waves are deduced. Through parameter analysis, the influencing factors and the influencing rules of subsoil degradation on ground motion response are discussed. The progress of subsoil degradation and postliquefaction characteristics have been elucidated.4. Exploring the proposed simplified models and Fourier and Reverse Fourier Transform methods, a theoretical solution in time domain for ground motions under dynamic loadings is presented. By numerical calculation, the characteristics and influencing rules of subsoil degradation on ground motions are analyzed. The reasonability and reliability of the solution are verified by large shaking table testing results.5. Analyzing the theoretical solutions in time domain and in frequency domain of the proposed simplified models, quantitative characteristics of subsoil degradation and seismic wave spectra are extracted. Quantitative influencing indices are defined and proposed. The correlation and interaction rules of subsoil degradation progress and seismic wave characteristics are established. Preliminary acquaintance of the correlation and interaction rules are obtained.更多还原