诱发各向异性砂土液化的双向单剪实验与离散元集成方法研究

On the study of the liquefaction of sand in complex stress conditions, due to the limitations of apparatuses, the macroscopic and microscopic behaviour of sand with induced anisotropy is not well understood. In geotechnical testing, due to the limitations of boundary conditions and shape of specimens, few apparatuses are capable of applying two directional shear stresses, and the complete stress condition of the specimen is difficult to determine. This study proposed an integrated method that combines the bi-directional simple shear testing and disrete element modelling. In the study on sand, by using the testing method and macroscopic results in bi-directional simple shear testing, build and verify a 3D discrete element model, study the anisotropy of sand particles and noncoaxiality of sand, then use the macroscopic and microscopic behaviour of sand in modelling to further study the stress state in bi-directional testing. Build a new integrated method that combines the bi-directional simple shear testing and disrete element modelling for analyzing sand liquefaction in complex stress conditions. This study provides microscopic mechanic behaviour for developing constitutive soil models in complex stress conditions. Result of this study will directly facilitate the understanding of microscopic behaviour of sand liquefaction in complex stress conditions, promote the development of the mechanics of sand liquefaction, provide a new method for solving complex scientific and engineering problems.

在对复杂应力条件下砂土液化的研究中,由于实验设备的局限性,未能很好地研究诱导各向异性砂土的宏观和细观特征。岩土工程实验室实验中，由于边界条件和试样形状的限制，能够同时加载两个方向剪力的仪器十分有限，而且试样的完整应力状态很难测得。本项目研究以砂土为研究对象，采用结合双向单剪实验和离散元数值模拟的方法，基于实验室双向单剪实验的测试方法和所得宏观结果，建立并验证双向单剪实验的三维离散元模型，研究模拟中砂土颗粒细观各向异性和非共轴特性的发展规律，进而用离散元模拟的试样内力和细观结构特征对实验室双向单剪实验的应力状态进行深入研究，并最终建立结合实验和数值模拟分析复杂应力条件下砂土液化的新方法，为复杂应力条件下砂土本构模型提供细观力学的基础。研究成果直接影响人们对复杂应力条件下砂土液化的细观认知，促进砂土液化机理理论的发展，为解决复杂科学和工程问题提供新方法。

本项目以砂土为研究对象，采用结合双向单剪实验和离散元数值模拟的方法，基于实验室双向单剪实验的测试方法和所得宏观结果，建立并验证双向单剪实验的三维离散元模型，研究模拟中砂土颗粒细观各向异性和非共轴特性的发展规律，进而用离散元模拟的试样内力和细观结构特征对实验室双向单剪实验的应力状态进行深入研究，并最终建立结合实验和数值模拟分析复杂应力条件下砂土液化的新方法。研究表明：离散元方法有助于更好地了解单剪试样内的应力状态，可用于修正应力的理论计算公式以对试验中砂土试样的应力状态进行分析；当砂土中存在固结剪力时，砂土颗粒之间的接触力数量将减小，最终导致砂土更易于液化；当砂土中的固结剪力与动荷载成90度或接近90度夹角时，砂土颗粒之间的接触力数量将迅速减小，并更易于液化；在工程中应着重避免或预处理带有初始剪力的砂土，尤其是初始剪力和循环荷载垂直时，以减少动荷载对砂土地基的影响。