Finite Element Analysis of Characteristics of Composite Foundation with Long-short-piles under High-rise Building

A case of the long and short piles composite foundation in liquefied soil under a high-rise building was taken.By using the finite element method,the effects of upper stiffness,cushion thickness,long pile length,long pile replacement ratio,short pile replacement ratio,raft thickness on average settlement,differential settlement,pile-soil stress ratio,pile-soil load-sharing ratio of composite foundation with long-short-piles were discussed separately.The results show that the upper stiffness had a limited effect on composite foundation;cushion thickness had a significant effect on the force characteristics of pile-soil;Long pile length had a significant effect on controling average settlement,and improving foundation bearing capacity and stress concentration of the top of the pile.Long pile replacement ratio varied in a reasonable range;short pile replacement ratio had a little effect on the stress and deformation of pile-soil;Differential settlement could be reduced with raft thickness increment.These conclusions provided references for future optimum design.