浅表砂层地震液化大变形物理机制与弹塑性本构研究

The proposed research is in the area of soil dynamics and sand liquefaction theory. The main focus of this project is the study of mechanism and elastoplastic constitutive model of liquefaction-induced large deformation of near-surface saturated sand before and after liquefaction. Systematic and high-precision experiments will be performed based on the latest low confining pressure static-dynamic triaxial test instrument. In the cyclic tests, the initial void ratio, initial consolidation pressure, initial shear stress ratio, dynamic shear stress ratio and frequency will be changed, and the new development laws of over consolidation, structural and stress-induced anisotropy under low confining pressures will be revealed. A modified elastoplastic model with rotation hardening which can systematically describe the monotonic and cyclic mechanical behaviors of soil combining the subloading, normal and super-loading yield surfaces will be established based on the experimental data. This model can uniquely describe the overall mechanical properties of soils under general confining pressure, without changing the values of parameters. The Green-Naghdi rate tensor will be adopted in the constitutive modeling and finite element analysis to consider the nonlinearity of both materials and geometry. In view of the new constitutive model and two-phase field theory, an effective stress-based, fully coupled, explicit finite element-finite difference method (FE-FD) will be conducted for the large-scale seismic response analysis of liquefied ground. This basic research will make a unique contribution to our understanding of the occurrence, development, spatial and temporal distribution of earthquake damages on the liquefied sites, reveal the disaster mechanisms of near-surface saturated sand. Projects from this proposed research will also provide important economic returns and social benefits for the new model can predict propagation behaviors of strong ground motions in the complex sites.

本项目旨在探索浅表饱和砂层在地震液化前后的大变形物理机制及其弹塑性本构表征这一难点问题。利用低围压静-动三轴试验仪，控制试验的初始孔隙比、固结压力、初始静剪应力比、动剪应力比和振动频率，通过系统而高精度的试验，揭示低围压下浅表砂层超固结、结构性和应力诱导各向异性在循环荷载作用下的耦联发展规律；基于张量推导，给出三者具有明确物理意义且简洁的发展式，完善基于移动硬化准则，融合修正剑桥模型和上、下负荷面剑桥模型的砂土静-动统一弹塑性本构。理论建模与有限元分析中引入能同时考虑土体材料与几何非线性、具有客观性的Green-Naghdi速率张量，实现大变形力学特性的合理描述。基于验证后的新建本构，构建新型液化场地弹塑性大变形地震反应分析程序。该项基础研究在重大自然灾害形成机理与预测领域能解决共性和关键问题，进一步提高对液化场地地震动传播行为的把握，具有重要的科学价值和社会、经济效益。

本项目意在解决浅表砂层地震液化前后的大变形物理机制及其弹塑性本构表征这一难点问题。利用低围压静-动三轴试验仪，控制试验的初始孔隙比、固结压力、初始静剪应力比、动剪应力比和振动频率，通过高精度的试验，初步揭示了低围压下砂土状态变量超固结、结构性和应力诱导各向异性在循环荷载作用下的发展规律；基于张量推导，给出了具有物理意义的发展式，完善了基于移动硬化准则，融合修正剑桥模型和上、下负荷面剑桥模型的砂土静-动统一弹塑性本构。理论建模与有限元分析中引入了能同时考虑土体材料与几何非线性、具有客观性的Green-Naghdi速率张量，实现了土体大变形力学特性的合理描述。基于验证后的新建本构，构建了液化场地弹塑性大变形地震反应分析程序。该项基础研究在重大自然灾害形成机理与预测领域能解决共性和关键问题，可进一步提高对液化场地地震动传播行为的把握，具有重要的科学价值和社会、经济效益。