Abstract: 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.

Key words: Wuhan Yingwuzhou Yangtze River bridge, north anchorage, open caisson foundation, underground protective wall, FLAC^3D