采用大型有限差分软件FLAC^3D，建立了武汉鹦鹉洲长江大桥北锚碇沉井基础的整体三维有限差分计算模型。对无地下防护墙（方案1）、地下防护墙入土深度50 m（方案2）及入土深度55 m（方案3）3种不同防护措施下沉井的下沉过程进行了数值仿真研究。分析了3种方案下沉井动态施工过程中沉井结构和周围地基土体的应力和变形特征，评价了不同防护措施的防护效果，为确定合适的地下防护墙入土深度提供了依据，并对设计方案的合理性进行论证。研究结果表明：3种方案下，沉井结构和周围地基土体的应力变形随开挖步骤的变化规律基本相似，入土深度越深，沉井及周围土体的变形相对减小而应力变化不大，但程度有限。防护墙的主要作用在于防治沉井下沉过程中出现的翻砂等不利情况，因此地下防护墙的入土深度需穿过砂层，沉井下沉翻砂时切断砂源，减少防护墙外地面变形。

The present research is to investigate the protection schemes for the open caisson foundation of bridges. The north anchorage open caisson of Yingwuzhou Yangtze River bridge in Wuhan is taken as a case study. Finite difference software FLAC^3D was employed to establish a holistic 3-D finite difference computation model of the caisson. Three protection schemes were selected: open caisson with no  underground protective wall (case 1), with the underground protective wall of 50 m depth (case 2), and underground protective wall of 55 m depth (case 3). The dynamic undrained sinking process of the north anchorage caisson were simulated, and the stress and deformation characters of the structure and the surrounding soil during the sinking process were analyzed. Moreover, the effect of the protection measures were evaluated, which provided basis for the determination of appropriate depth of the underground protective wall. And the rationality of the design scheme was verified as well. Results showed that the laws of deformation and stress variation of the caisson and its surrounding soil in the three cases were generally similar: deformation of the caisson and its surrounding soil decreased slightly with the increase of buried depth of underground protective wall, while the stress remained constant. Since the protective wall is to prevent quicksand in the process of sinking, it should penetrate through the sand layer to cut off the sand source in order to reduce ground deformation.