强震作用下饱和砂砾土液化的细观力学机制研究

Gravelly soil is often mistaken as a non-liquefied soil and has been widely used in the engineering. However, gravelly soil liquefaction is one of the prominent features of the hazards in the Wenchuan earthquake, and it is still a lack of meticulous cognition about its liquefaction mechanism. The typical liquefied gravelly soil in Wenchuan earthquake regions is studied by combination of the macro-mesoscopic methods, and a series of large dynamic triaxial tests, CT scan tests and PFC numerical simulations are carried out to study the meso-mechanism of saturated gravel soil liquefaction under strong earthquakes based on its multi-scale structures of particle-force chain-system. The main research contents include the followings: (1)the liquefaction characteristics tests of saturated gravelly soil are carried out to establish the energy-based model of pore water pressure development, and the evolution characteristics of gravelly soil meso-fabric during liquefaction is analyzed by the CT scan technique; (2)by means of the discrete lattice Boltzmann method, the immersed moving boundary method is introduced to develop solid-liquid bidirectional coupling analysis program on basis of the Particle Flow Code (PFC) so as to realize the simulation of gravelly soil macroscopic liquefaction tests; (3)a reasonable criterion for the force chain networks is proposed so as to study the law of their dynamic evolution during the gravel soil liquefaction, and a structural mechanics analysis model based on force chain buckling deformation is estiblished to reveal the liquefaction meso-mechanism of saturated gravelly soil under strong earthquakes. Findings could not only improve the cognitive level of saturated gravelly soil liquefaction, but also provide a scientific foundation for the seismic design and safety evaluation of the hydraulic and civil foundation engineering.

砂砾土常被误作为非液化土体在工程中广泛应用，然而砂砾土液化是汶川大地震突出的致灾特征之一，对其液化机理尚缺乏精细化认知。项目以汶川地震区典型液化砂砾土为对象，采用宏细观结合的方法，借助大型动三轴、CT扫描试验和颗粒流数值模拟，基于其"颗粒-力链-体系"的多尺度结构，阐明强震作用下饱和砂砾土液化的细观机制。主要内容包括：（1）进行饱和砂砾土液化特性的大型动三轴试验，建立孔压-能量增长模式，借助CT试验分析其细观组构的演化特征；（2）利用离散格子玻尔兹曼法，通过浸入运动边界法，进行基于PFC的固液双向耦合分析的二次开发，实现宏观液化试验的细观颗粒流模拟；（3）构建合理的力链网络判据，探讨砂砾土液化进程中力链网络的动态演变规律，建立基于力链压曲变形的结构力学分析模型，揭示其液化特性的细观力学机制。研究成果有望提升对砂砾土液化的认知水平，且可为我国水利、土木工程的抗震设计与安全性评价提供科学依据。

砂砾土常被误作为非液化土体在工程中广泛应用，然而砂砾土液化是汶川大地震突出的致灾特征之一，而关于砂砾土振动液化机理的研究则鲜见报导，尤其从细观尺度来揭示饱和砂砾土的液化机制尚缺乏深入和系统的研究。本课题基于砂砾土液化的研究现状以及颗粒介质细观力学机制研究的最新进展，将颗粒物质力学与土力学理论相融合，开展饱和砂砾土动三轴液化试验、CT扫描试验和细观颗粒流数值模拟，以颗粒细观力学理论为基础，从细观组构和力链的演化出发，深入研究饱和砂砾土地震液化的力学响应机理。研究成果可为我国水利、土木工程的抗震设计与安全性评价提供科学依据。主要工作内容如下：.（1）采用CT技术，对饱和砂砾土试样进行初始状态扫描，4种级配的试样制备都比较均匀。同一相对密实度的砂砾土，当含砾量较低时，砂粒填充在骨架孔隙内并部分悬浮在砾粒骨架间，将砾粒之间的接触分隔开来，随着含砾量的增加，砂粒完全填充在骨架孔隙内，砾粒与砾粒之间的接触逐渐增强。.（2）利用全自动三轴仪进行了饱和砂砾土固结不排水剪切试验，在同一围压，同一相对密实度情况下，随着含砾量的增加，饱和砂砾土应力应变关系由应变软化型向应变硬化型转变，同时峰值强度明显提高，且随着含砾量的增加逐渐升高；孔压则随含砾量的增加呈下降的趋势，剪胀趋势更加明显。.（3）利用GDS循环三轴仪进行了一系列饱和砂砾土等应力和等应变加载动三轴液化试验，研究了饱和砂砾土在两种加载方式作用下的液化特性，分析了含砾量对饱和砂砾土动强度和动孔压的影响规律，并从粒间状态参量出发，分析了含砾量对饱和砂砾土动强度和动孔压的影响机制。.（4）采用fish语言开发了不同粒组级配土样离散元仿真模拟分析方法与细观组构参量统计分析的子程序，在此基础上对饱和砂砾土的液化过程进行了细观颗粒流数值模拟，获得到了细观组构和力链的演化规律，揭示了强震作用下饱和砂砾土液化的多尺度力学机制。