Abstract: Under large-area loading around existed pile group foundation, the pile shaft was not only loaded by negative friction, but also by extra horizontal force. With the pile group foundation of bridge passing through deep soft soil in a newly built cofferdam project for example, a 3-D finite element model was established to simulate the loading process. The simulation results indicate 1) large-area loading has negative effect on the pile foundation, and the effect is significantly dominated by pile-soil friction coefficient which is different to be determined in actual engineering; the pile-soil friction coefficient in the study case was determined in the range of 0.2-0.3 through comparison between negative friction around pile foundation in numerical simulation and standard lateral friction resistance of foundation soil in in-situ test; 2) negative friction around pile foundation can be generated by the filling materials, hence increasing the axial force of pile foundation, yet with no damage; 3) filling symmetrically and evenly could alleviate to the largest extent the uneven settlement of pile foundation and confine the horizontal diffusion of additional loads to the deeper soil; the influence on the bending moment of pile shaft can also be controlled; 4) due to the difference in spatial distribution of pile group, the compatibility of pile-soil deformation below the same cushion cap induced by the additional loads is different, hence the safety monitoring for bridge pile should be targeted.

Key words: embankment filling, large-area loading, soft soil foundation, pile group foundation, negative friction, 3D finite element