桩靴基础是支撑自升式钻井平台进行海洋油气勘探的主要基础形式，但复杂的海洋土分布和恶劣海上荷载的共同作用却导致基础失效事故频频发生，由于多种失效模式并存，桩靴基础在复杂海洋土中的失效机理尚不清楚。本项目针对海洋土的复杂空间变异性（内因）和荷载的随机多向性（外因）两个方面深入研究桩靴基础的多模式失效及其机理、多元荷载下的承载力及其包络面。通过大尺度模型试验和随机场大变形数值方法，深入研究桩靴基础安装过程中剪切破坏与土体空间变异性的相互作用，进而对“复杂海床-桩靴基础-多向荷载”之间的耦合力学机理进行系统研究，揭示土体空间变异特征的作用规律，建立复杂海洋土中桩靴基础在组合载荷下的承载力包络面数学模型及置信水平，提出基础的稳定性评价方法。本研究在揭示复杂海洋土中失效机理的基础上，提出考虑土体空间变异性和多元荷载耦合效应的桩靴基础稳定性分析方法，为海洋油气勘探开发中自升式平台的风险评价提供系统方法。

Spudcan foundation is an important type of offshore foundation to support the jack-up platforms for offshore oil and gas exploration. However, this type of platforms experienced considerable fatal failures in the past few years. The main reason is that multiple potential failure modes and the corresponding mechanisms of the spudcan foundation remain unclear under the coupled effects of the complex soil properties and the harsh offshore loading environments. This project will study the multiple failure modes, the bearing capacity and the failure envelopes of the spudcan foundations considering the spatial variability of the offshore soil (internal cause) and the multidirectional random loadings (external cause). Large scale model experiments and the random large-deformation numerical methods will be developed, which provide the necessary techniques to analyze the interaction between the spatially variable soil and the shear path. The coupling effects of “complex seabed-spudcan foundation-combined loading” will be systematically studied. Based on these works, the spatial variability of the seabed will be revealed. Mathematical model for the failure envelope will be established for the spatially variable soil under combined loadings. Moreover, the confidence levels of the model will be investigated probabilistically. Finally, the risk assessment method for the foundation will be proposed. This study will provide new methods to analyze the stability of the spudcan foundation considering the coupling of the complex soil and the combined loading based on the study of failure mechanism. The results from this project will enable a rigorous risk assessment of jack-up platforms in oil and gas exploration as well as offshore site investigation.