地震波与液化土层特征关联性及相互作用规律研究

Wave propagation in soil medium is an important scientific subject in strong motion seismology and engineering seismology. The influence of soil liquefaction on ground motion and liquefaction detection techniques based on ground motion records, which, respectively, belong to direct and inverse problems, are new proposals which need to be solved in engineering practice. Presently, the acquaintance and understanding of the problems are quite superficial as well as limited theoretical background. The keys to solve the problems depend on understanding the correlation of seismic wave and liquefied soil characteristics, meanwhile, and their interacting rules. In this project proposal, in-situ investigation documents analysis, laboratory testing and theoretical calculation are comprehensively used methods, in terms of correlation of seismic wave and liquefiable soil along with their interacting rules, to study the time variation process of ground motion records. Thereafter, the characteristics and seismic wave can be collected and furthermore their liquefaction influenced threshold values will be proposed. By establishing a liquefaction influenced theoretical model, soil property characteristics can be obtained and their liquefaction influenced threshold values will be proposed. The correlation of the characteristics of seismic wave and soil under existing liquefiable layers is studied and then corresponding correlative curves will be plotted to understand the fundamental interacting rules of seismic wave and liquefied soil. The project can promote the theory of wave propagation in complex soil medium and provide theory background for influence of soil liquefaction on ground motion and liquefaction detection techniques.

土体中波传播问题是强地震学和工程地震学的重要研究内容。土层液化对地表地震波影响以及从地表地震波识别液化是工程上新近提出需要解决的课题，分属于波正反演问题，目前均处在局限于表面现象粗浅认识阶段，理论基础匮乏，而解决这两方面问题的关键均在于地震波与液化层特征关联性的认识及二者相互作用规律的掌握。本项目从地震波-液化层关联性及相互作用角度统一考虑，采用现场资料分析、室内实验和计算分析等多种手段，研究各类土层地表地震记录时变过程，提炼液化层存在下地表地震波特征，提出地震波特征液化影响阈值；建立土层液化影响理论计算模型，获取土层性能特征，提出土层性能特征液化影响阈值；研究液化层存在下地表地震波特征量与土层特征量的关联性，建立不同条件下两类特征量变化的关系曲线，掌握地震波与液化土层相互作用的基本规律。本研究可发展复杂土层中波传播理论，并为解决液化层对地震波影响以及从地震波反演识别液化问题提供基础。

通过对几种典型场地地震动记录的对比分析，对液化场地地震特征有了深入认识。硬土场地、软土场地和液化场地上的地震动特征具有明显区别，三者层次清晰，差别显著，从地震动表现上液化场地已构成一个与常规场地并列的独立单元；以三质点体系代表具有液化夹层的普适性场地，提出了土体液化引起场地卓越周期变化的解答，得到了土层及液化层特征量对场地卓越频率的影响规律；以地震下土体剪应变衰减为出发点，对土体弱化程度进行整体等级划，采用简化理论模型，初步研究了土体不同弱化程度与地震动特征相对变化的关系。采用新型高精度动三轴仪，通过试验方法研究动荷载作用下循环最大剪切模量和循环极限剪应力随孔隙水压力变化模式和规律，寻求更符合实际的孔压增长下循环最大剪切模量和循环极限剪应力的计算公式，进而对液化场地动力反应分析方法进行了改进。通过振动台与现场激振的液化试验，研究了液化场地与非液化场上地震动的差别，分析了液化与地震动的关联特性。