Abstract: Optimization of group piles below a rigid raft is analyzed; and load carried by individual pile is adjusted by the length of pile, respectively. To analyze elastoplastic behaviour of piles, a “cut-off” method is adopted to limit pile capacity in the integral equation considering linear behaviour of piles; and then the optimization results are easily obtained. The analysis shows that the corner piles reached to their bearing capacity at first; and then the side piles come at their bearing capacity gradually with redistribution of extra loads of the corner piles. With the increase of acting loads, the inner piles come into ultimate state finally. In that case, the whole piled raft system reach to failure state at the same time. A “cut-off” method can be used to improve the foundation design based on the optimization of variable rigidity, which is more consistent with the actual situation.

Key words: cut-off method, long-short piles, optimization analysis, rigid cap, elastoplasticity