考虑砂土材料颗粒形态及孔隙水压的多尺度模拟

Granular sand underpins the operation and performance of key infrastructures in civil and mining engineering and petroleum industries, including buildings, highways, slopes, water dams, embankments, tunnels, on/offshore foundations and reservoir boreholes. Natural hazards involving sand, such as landslides and debris flow, constitute a major challenge for many countries around the world. Sand is multiscale and multiphase in nature. While it can be largely regarded a continuum, it is the underlying interactions and microstructural mechanisms among the constituent particles at the micro/meso scales that play a decisive role in dictating its macroscopic response. Sand is meanwhile a deformable porous medium with its pores being fully or partially saturated with water. The coupling between pore fluids and sand skeleton affects many complex behaviors in sand such as liquefaction and failure. It has been a major challenge to account for both the multiscale and multiphase natures in the modeling and characterization of sand behavior. ..The proposal aims to develop a computational framework to capture the multiscale and multiphase natures of sand response relevant to geotechnical applications. The framework will employ a rigorous hierarchical coupling between finite element method (FEM) (for the continuum scale) and discrete element method (DEM) (for the meso/micro scale) to develop a rigorous multiscale-modeling tool for sand. The new framework features a thorough consideration of realistic morphology of sand grains on the meso/micro scale modeling and incorporates a fully coupled hydro-mechanical formulation at the macro scale to account for the influence of pore water presence in saturated sand. Key effective variables and hydraulic properties required for advancing the macro FEM solution will be derived directly from the meso-scale simulations in the multiscale framework. The entire framework will then be benchmarked, calibrated and verified before being applied to solving practical geotechnical problems...The proposed research will offer an integrated and robust methodology combining the strengths of both continuum approaches and micromechanics-based ones for sand modeling and provide a powerful predictive tool for next-generation design in civil/mining/petroleum engineering. The tool will help on effective modeling, prediction and mitigation of natural geohazards commonly occurring in mainland China, Hong Kong SAR and other areas, such as landslide, debris flow and failure of earth structures.

砂土力学性质复杂，但其工程意义重大。砂土具有典型的多尺度和多相特性，其宏观特性是由细观颗粒相互作用及其细观结构所决定的，同时孔隙水与土颗粒骨架间的相互作用也影响砂土的很多复杂行为。考虑砂土材料的多尺度及多相特性一直是模拟砂土力学行为的重大挑战。本项目建议采用有限元与离散元耦合的方法对砂土进行多尺度模拟，在细观模型上考虑真实砂土颗粒形态影响，并在宏观控制方程中利用有效应力原理考虑饱和砂土的水土耦合作用。宏观有限元求解所需的关键变量如有效应力和渗透系数，将直接由细观离散元模拟所得到。该框架能有效避免传统连续介质力学的各种唯象假设，将砂土各种宏观现象与其决定性的细观物理结构及变化直接关联起来，还能够简单有效的考虑孔隙水体对土体的重要影响。该多尺度计算力学框架不仅有助于促进土力学的研究，也为未来解决岩土工程中重大疑难问题提供一种突破性的新工具。

砂土是土木、水利、矿山、地下工程及油气田开采过程中主要承受外荷载的材料，其力学性质复杂，与各种外力荷载及复杂因素密切相关，砂土破坏是诸多工程事故的首要原因。工程问题中砂土具有典型的多尺度和多相特性，其宏观特性和水力力学反应是由细观颗粒相互作用及其细观结构所决定的，同时孔隙水与土颗粒骨架间的相互作用也影响砂土的很多复杂力学行为。考虑砂土材料的多尺度及多相特性一直是模拟和理解砂土力学行为的重大挑战。本项目经过四年的研究，采用了包括有限元、物质点法与离散元耦合的方法对砂土进行多尺度模拟，通过基于聚超椭球体的颗粒形状描述，在细观模型上高效率地接近考虑真实砂土颗粒形态影响，并在宏观控制方程中利用有效应力原理考虑饱和砂土的水土耦合作用。宏观有限元或者物质点法求解所需的关键变量如有效应力和渗透系数，直接由细观离散元模拟所得到。该框架有效避免传统连续介质力学的各种唯象假设，将砂土各种宏观现象与其决定性的细观物理结构及变化直接关联起来，还能够简单有效的考虑孔隙水体对土体的重要影响。本研究建立了包括有限元与离散元耦合应用于中等变形的多尺度计算方法，同时还扩展到物质点法与离散元耦合的用于大变形破坏的计算方法。项目后期还进行了创造性的扩展，基于近场动力学与物理引擎耦合的方法对砂土颗粒破坏进行研究，同时将该多尺度计算方法扩展至考虑温度荷载的影响。该项目研究成果不仅大大促进土力学基础理论和数值方法研究的发展，也为未来解决岩土工程中重大疑难问题提供一种突破性的新工具。该项目提出的多尺度计算力学框架和方法及其扩展代表了该领域最前沿的开创性的成果，在全球范围内得到广泛承认和认可，项目的研究成果论文得到大量追踪和应用并获得各种奖项，项目负责人多次应邀在世界著名学术会议上做大会报告，并于2020年开始担任著名岩土期刊Computers and Geotechnics共同主编，项目培养的研究生和博士后也成长为国内外著名大学科研的中坚人才。