大跨度悬索桥嵌桩式重力锚碇承载机理和稳定性分析

Analysis of Load Carrying Mechanisms and Stability of Pile-Supported Gravity Anchorages for Long-Span Suspension Bridges

悬索桥重力式锚碇具有传力机理简单及对地质条件适应性强的优点,但其缺点是体积庞大、造价昂贵、对环境扰动大。近年来,一种旨在显著减小重力锚体积的新型嵌桩式重力锚结构引起工程界的关注,但对于此类锚碇基底摩阻力和嵌固桩所分担的抗滑力随主缆荷载的变化规律以及这种锚碇的失稳破坏机理尚不清楚。本文采用非线性弹塑性有限元方法、Drucker-Prager屈服准则以及非线性接触-摩擦单元,分析了位于中风化石英砂岩地基上大直径嵌桩式重力锚的承载机理和稳定性,研究表明:嵌固桩承担总抗滑力的70%~80%,而锚碇摩阻力承担抗滑力的20%~30%;嵌桩式重力锚的抗滑稳定性系数可以达到2.0,嵌桩式重力锚的失稳主要由锚碇后部嵌固桩周围基岩局部破坏而引起;与齿坎式重力锚相比,嵌桩式重力锚可以减小锚碇自重达20%以上,具有较好的工程应用前景。

The gravity anchorage for suspension bridges has the advantages of simple load transfer mechanisms and good adaptability to a variety of geological conditions.However,it has disadvantages of huge volume,high construction cost,and severe disturbance to the environment.In recent years,a new type of gravity anchorages,which are supported on rock-socketed piles to reduce the anchorage volume,has attracted the attention of the engineering community.Nevertheless,the proportions of the slip-resistance from the rock-socketed piles and from the friction on the bottom of the anchorage,their variation with cable force,and the stability and failure mechanism of the anchorage,have yet to be understood.In this paper,nonlinear elasto-plastic finite element method with the Drucker-Prager yield criterion and nonlinear contact-friction elements are utilized to analyze the load-carrying mechanisms and stability of the large-diameter pile-supported gravity anchorages on the mediumly weathered sandstone.It is shown that the pile generally takes 70%-80%of total slip-resistance,while the friction only takes 20%-30%of it.The anti-slip stability coefficient of the anchorage can reach 2.0,and the instability is mainly caused by the local failure of the bedrock around the rock-socketed pile at the back of the anchor.Since the pile-supported gravity anchorages can reduce the self-weight by 20%compared with the gravity anchorages with tenon,this type of anchorages has good potential to be used in the long-span suspension bridges.