砂砾土液化特性的缩尺效应及其弹塑性本构模型研究

The liquefaction of sand gravels was certificated in several earthquakes and the constitutive model is much significant theory foundation .for the evaluating the stress and deformation of sand gravel ground during liquefaction and post liquefaction.Because of the limitation of. the facilities's size, the scale grades were often used to investigate the behavior of sand gravels. However, the scale effect impact on the dilatancy and constitutive model had been investigated to a very limited extent and without careful examinations. A series of large static .and cyclic triaxial tests with different specimens sizes of the sand gravel will be performed to study the scale effect on the dilatancy,critical state and liquefaction properties. The dilatancy equation and the expression of critical state line suitable for sand gravel will be proposed .and the elasto-plastic model will be established to take into account the scale effect and various stress path. On this basis, elasto-plastic .static and dynamic analysis method and simulation software for the whole liquefaction and post liquefaction process of sand gravel will .be developed with considering the large deformation by using remesh and stress interpolation. The stress and deformation of sand gravel liquefaction triaxial tests and Hanshin earthquake will be simulated to verify and improve the model and analysis method. Based on the therical analysis and numerical simulation, the liquefaciton mechanism and development process of sand gravel will be revealed, and the discriminating standard of sand gravel liquefaction and its correlated factors will be presented. Finally, the anti-liquefation measures will .be suggested.

砂砾土发生液化已经过多次震害证实。砂砾土的本构关系是砂砾土场地液化和液化后应力与变形分析的理论基础。受试验设备的限制，常采用缩尺级配进行砂砾土液化特性研究，但缩尺效应对砂砾土的剪胀规律和本构模型影响尚不清楚。本项目拟通过不同尺寸大型静、动三轴仪，对发生地震液化的砂砾土选取代表性现场全级配，进行大量的试验研究，重点分析砂砾土的剪胀特性、临界状态特性和液化特性的缩尺效应，考虑缩尺效应和复杂加载条件，建立适合砂砾土的剪胀方程和临界孔隙比关系，据此构建砂砾土的静、动力弹塑性本构模型。在此基础上，引入网格重剖分和应力插值的大变形分析方法，建立能够描述砂砾土液化及液化后全过程应力与变形发展的数值模拟方法。通过砂砾土三轴液化试验和阪神地震砂砾土液化震害数值模拟，验证并改进本构模型和分析方法，进而揭示砂砾土的液化机理和灾变过程，提出砂砾土液化的综合判别标准，建议合理有效的砂砾土场地抗液化措施。

本项目对砂砾土开展了系统且深入的研究：把握特征状态点（相位变换点、峰值点及临界状态点）特性，构建了能够合理反映砂砾土材料剪切全过程的非线性剪胀方程；建立了饱和砂砾土实用化的静动统一弹塑性本构模型，为深入研究其液化特性及主要影响因素奠定了理论基础；开展了防波堤地震液化及液化后再固结的全过程弹塑性分析，结果表明，考虑液化后孔压消散的固结过程计算得到的地震沉降变形增加了约50%。研究成果可望为砂砾土结构，如面板砂砾石坝，人工填海，核电厂防波堤等等工程提供科学基础与技术支持。