基于细观的流固耦合方法对吸力式桶形基础土塞形成机理的研究

As the oil & gas exploration and development move to deep-sea area, the suction bucket foundation is widely applied to the construction of offshore platforms in recent years. In practice, the pull-out capacity of the bucket foundation will greatly depend on its penetration depth which is significantly influenced by the soil plug inside the bucket. In this project, a CFD-DEM coupled method, which is able to describe the meso-scale pore fluid flow and micro-scale solid phase deformation, will be developed to simulate the installation of suction bucket foundation in saturated soil in deep sea. Centrifuge tests will be utilized to validate the newly-developed numerical method. And the influence of key microscopic parameters, i.e., particle size, particle stiffness, particle-particle strength, particle-particle friction, on the soil plug inside the bucket will be investigated and the meso-scale mechanism of soil plug formation and evolution in three types of soil, such as, sand, silt and clay, will also be studied in means of numerical modelling and centrifuge tests. The aim of this project is to explore the meso-scale mechanism and mechanical effects of soil plug, and further to pave the way for solving the soil plug problem in design and construction of the suction bucket foundation in the future.

随着海洋油气资源的勘探开发逐步向深海推进，吸力式桶形基础在海洋平台结构建设中得到了广泛的应用。在实际工程中，桶基能否下贯到设计深度将直接影响到它能否发挥抗拉拔承载能力，而桶基最终贯入深度主要受桶基内部形成的土塞的影响。本项目以吸力式桶形基础沉贯过程中产生的土塞为研究对象，结合海洋土力学特点，基于CFD和DEM计算理论，拟发展一套能够从细观层面上描述土体中孔隙水与土颗粒之间相互作用的流固耦合数值模拟方法，综合离心机实验的研究手段，检验上述模拟方法的有效性和准确性，并进一步分析土颗粒粒径、颗粒刚度、颗粒接触强度、颗粒间摩擦系数等细观参数对土塞的影响，探讨土塞的力学效应以及三种不同土质（包括砂土、粉土和黏土）中形成土塞的特点。目的是从细观力学层面上探明土塞现象的形成机制和发展规律，正确评价土塞的力学效应，从而为进一步解决吸力式桶形基础设计、施工中的土塞问题建立理论基础。

本项目是在国家海洋开发战略大背景指导下，主要针对海洋油气平台锚固基础吸力式桶形基础（吸力锚）在安装过程产生的土塞现象及其形成机理所开展的一项具有科学理论创新和实际应用价值的研究。研究结合海洋土力学特点，在水与土颗粒拖曳力模型、考虑粒径差异的流固耦合算法上取得了进展，基于计算流体动力学CFD和理算元DEM计算理论，发展了一套能够从细观层面上描述土体中孔隙水与土颗粒之间相互作用的流固耦合数值模拟方法及程序；使用离心机试验研究手段，检验所开发数值模型的有效性和准确性，并进一步分析土颗粒粒径、颗粒刚度、颗粒接触强度、颗粒间摩擦系数等土体细观参数对土体宏观变形及土塞的影响；并进一步探讨土塞的力学效应以及不同土质中形成土塞的特点，从细观力学层面上探明了土塞现象的形成机理和发展规律，进而正确评价土塞的力学效应。项目研究取得的成果为进一步解决吸力式桶形基础设计、施工中的土塞问题建立了理论基础。