Seismic Response Of Composite Cement Mixing Pile Foundation With History Analysis Method

The study on the seismic response of cement mixed pile foundation with earthquakes load is of great theoretical and practical importance in seismic design of engineering. The present state of research on cement mixed pile foundation is summarized in this paper firstly, then the paper points out that the effect on dynamic properties for the composite foundation from different superstructure, the modulus of compressibility of compound soil, the modulus of compressibility of soil and the depth of cement mixed pile, which are not properly solved in engineering practice nowadays. Thus the research purpose and the practical meaning of this paper are point out.This paper defines the compound soil as the cement pile and soil among piles. Also a body system of FEM on superstructure-foundation-composite foundation is established. In which we take the compound soil and soil as visco-elastic material, and superstructure and foundation as elastic material. By parametric study and comparative analysis, the paper studies the effect on dynamic properties for the composite foundation from different superstructure, on which we consider the effect of which is zero floor, one floor, three floors and seven floors;the modulus of compressibility of compound soil, on which we consider the effect of which the value is 60MPa, 120MPa, 240MPa;the modulus of compressibility of soil, on which the effect of which is 4MPa, 8MPa, 16MPa and the depth of cement mixed pile on which the effect of which is 7m and 15m.Some significant conclusion can be drawn in this paper:(1) Compared with free field, considering the interaction of superstructure-foundation-composite foundation, the effect of the displacement, the velocity and the acceleration decrease dramatically. With the increment of floors of superstructure, the peak value of the displacement, the velocity and the acceleration of the cement mixed pile foundation are decreasing gradually, and in the same floor the reduction extent of these peak values inside the improved area are further than that outside. The peak values get its maximum value close to the ground. Besides, the closer site to the ground, the bigger value of peak displacement and peak acceleration we will get.(2) To the modulus of compressibility of compound soil, with its increment the peak value of the displacement, the velocity and the acceleration decrease dramatically inside the improved area. In the same time this trend becomes more distinct with the increment of floorsof superstructure. While outside the improved area, the peak value of the displacement and the velocity is decreasing, and the peak value of acceleration is increasing.(3) To the modulus of compressibility of soil, inside the improved area the peak value of the displacement decreases dramatically and that for the velocity and the acceleration are increasing with the increment of the modulus of compressibility of soil. This trend becomes more distinct than it with the modulus of compressibility of compound soil, which should pay attention in the practical design of engineering. While for the non-improved area, the effect is due to superstructure.(4) Increasing the improving depth of the cement mixed pile can dramatically decrease the peak value of the displacement and the acceleration inside the improved area. But the effect becomes unconspicuous outsides.All the conclusion above offer a theoretical basement to the design of foundation engineering.