Study On The Behavior Of The Rigid--Pile Composite Foundation With The Upper High Building

Rigid-pile composite foundation is a new method of ground improvement, which is defined to be used to support upper loads together by reinforced concrete piles (or concrete piles) and soil around.In this dissertation, a 3-D elastic-plastic model of the whole high-building is set up to systemically analyses the behavior of the composite foundation, in which the upper structure rigidity, modulus ratio of pile to soil,sand cushion and replacement ratio are taken into accounted. Some significant conclusions are obtained as follow:(l)With the increment of upper structure rigidity, specially reaching a fixed floor, the distribution of stress and settlement in the composite foundation keeps unchanged. This shows that upper rigidity has a limit effect on the foundation.(2)There is a best modulus of pile in the composite foundation. Because with the increment of modulus of pile, the limit effect on the foundation is showed.(3)The effect of sand cushion on the foundation is in the shallow depth (within 1/2 pile length). With the increment of sand cushion, the load ratio of the piles and the soil around can be adjusted, making the axial force of piles top less and the soil load much greater. But at the same time, the whole settlement is greater too. So, in the practical engineering, the depth of sand cushion is chosen to be reasonable.(4) There is a best replacement ratio of pile in the composite foundation. Because with the increment of replacement ratio, the effect on the foundation is limit.(5)The behavior of group piles under the raft is analyzed. A single pile's axial force lied on its position of the group piles, and side frictional force becomes greater down the pile's depth.Finally, a high-building case is analyzed. The results calculated with 3-D numerical analysis are closed to the measured results.