Dynamical Analysis Of The Cast-in-situ Concrete Thin-wall Pipe Pile Composite Foundation

A two-dimensional simplified model for dynamical analysis of cast-in-situ concrete thin-wall pipe pile composite foundation is advanced. The dynamic response under seismic load is calculated and the effects of the distance between each pile, the length and radius of pile, the wall thickness and the elastic ratio of the pile on the dynamic characteristics of composite foundation are explored with the FEM method. Main conclusions are described as follows:1. The dynamic response of cast-in-situ concrete thin-wall pipe pile composite foundation reactes strongly on the horizontal ground surface, and gradually decreases from the centre of the reinforced area to the marginal zone. The dynamic response on the reinforced vertical ground surface declines than former, the amplitude of dynamic response (acceleration, displacement) are smaller and are fluctuated on the surface ground of reinforced area.2. The horizontal maximum values of dynamic response declines from the top to the bottom and achieves the maximum value on the top;the dynamic response on the upper half of the reinforced area is stronger than un-reinforced area, but the lower half is opposite. The dynamic response of the pile is continuous along the length and its amplitude is smaller while that of the soil fluctuates widely.3. The horizontal dynamic deformation of the piles coincides with that of the soil, but the vertical deformation between the piles and the soil is not coincided well with that of the soil around, a difference existes.4. The maximum dynamic shear stress of the piles in the centre of the reinforced area is about half of the value of the pile on the margin in the reinforced area. The shear stress of soil in the middle of the reinforced areas is nearly equal with that of the marginal reinforced areas. The maximum dynamic shear stress in the reinforced area appeares in the 1/3 pile length under surface ground of the marginal piles.5. The dynamic response of surface gradually reduces as the distance between each pile increasing, the internal shear stress reduces as the distance increasing but increases a slight when the distance achieved to a certain value. The surface dynamic response of cast-in-situ concrete thin-wall pipe pile composite foundation on the reinforced area will decrease and the dynamic shear stress will became smaller while increasing the pile length within critical pile length, and the dynamic characteristic of the composite foundation will also increase. The dynamic response will increase at beginning and then decreases later when increasing the radius of the piles. The foundation surface dynamic response of R1.5m showes much better mechanical property. The change of the wall thickness of the pile has little effects on the dynamic response. But the maximum dynamic shear stress will decrease when the radius of the wall thickness increased. The coincident characteristics of the deformation between soil and piles under seismic load will be strengthened while the modulus of the piles decreased.