Abstract: Variable stiffness optimization design is always an important and difficult problem for large-scale pile-raft foundations in complex environments. In this article, a two-stage optimization method was developed using finite element analysis, According to the stress distribution on top of piles in the traditional design with uniform pile arrangement, the pile groups are divided into several sub-groups firstly. Then the adjustment coefficient of the number of piles is determined according to the relationships among the pile top stresses of every sub-group. Finally, by adjusting the spacing of piles to change the number of piles in each sub-group, the variable stiffness optimization design can be realized. This procedure is used to optimize the large-scale piled raft foundations with non-uniform superstructure loads in multi-layer soils. The results show that after optimal design, the differential settlement of the raft, the average overall bending moment and the differential stress at the top of the pile are significantly reduced. The method is simple in calculation and wide in application, and is not limited by complex soil conditions, non-uniform superstructure loads and the size and shape of the pile foundation.

Key words: variable stiffness optimization design, change pile spacing, large-scale pile-raft foundation, complex soil layer, non-uniform loads