软黏土中桶形基础的上限法极限分析模型及其计算

Limit Analysis and Calculation for Bucket Foundation Embedded in Soft Clay Based on the Upper-Bound Theorem

桶形基础作为近海工程一种新型结构形式,其结构与地基土体间复杂的相互作用使得此类结构的承载机理与破坏形态一直未有明确的界定,根据饱和软黏土中桶形基础的工作特点确立了其在侧向荷载作用下的一种新的三维组合破坏模式,基于塑性极限分析理论的上限法建立了受侧向荷载作用的、饱和软黏土中桶形基础的极限分析模型,运用非线性数学规划的Nelder-Mead改进单纯形法,并结合遗传算法对相关参数进行寻优,求得上述破坏机制的最危险模式及侧向荷载的最小上限解．根据桶形基础在不同插入深度时的承载机理及受力机制,将桶形基础结构划分为3种受力模式,即相对埋深小于0．52时的浅插式、相对埋深大于1．2时的深插式与介于两者之间的过渡模式,为结构整体稳定性分析计算提供了理论依据．此外,模型试验及工程实例的分析进一步证明了上述分析方法的可行性和有效性．

Bucket foundation embedded in in-place foundation soil is a new structure style of offshore engineering. Scholars have been in a puzzle about the bearing mechanism and failure mode of this structure under lateral loads especially the complicated interaction between the structure and the soil. A new combined three-dimensional failure mechanism of bucket foundation in undrained soft clay under lateral loads is established according to its performance, and based on the upper-bound theorem, the limit analysis model of bucket foundation under lateral loads is proposed. Nelder-Mead modified simplex algorithm with genetic algorithm is employed to optimize the relative parameters, then the most dangerous mode and the least upper-bound solution which is thought to be the optimal approximation to the real ultimate lateral load from the upper-bound are obtained by them. Aeeor-ding to the structure＇s bearing mechanism under different embedded depth-diameter ratios, bucket foundation is classified as three bearing modes, namely the shallow embedded bucket foundation when embedded depth-diameter ratio is less than 0.52, the deep embedded type when when embedded depth-diameter ratio is larger than 1.2, and the transitional mode between the former cases. This classification provides theoretical basis for structure＇s global stability analysis in design. It is proved from the physical model test and the practical engineering that the proposed upper-bound analysis model is feasible and valid.