Vibration Response Analysis Of CFG Pile-Gravel Pile Composite Foundation In Liquefiable Field

Foundation treatment can avoid the harm of sand liquefaction caused by earthquake.Multi-pile composite foundation can combine the advantages of different piles.Some scholars have obtained results on static problems of multi-pile composite foundation,but there are few dynamic analyses.In this paper,the dynamic response of CFG pile-gravel pile composite foundation in soil containing silty and fine sand interlayer is analyzed under earthquake action.Gravel pile mainly plays the role of dissipating pore water pressure,and CFG pile mainly provides bearing capacity ability.Fluid-solid analysis and dynamic analysis are involved in the process of sand liquefaction caused by earthquake.The interaction between structure and soil is inevitable when structure exists in soil,and there is also mutual influence between different structures.The finite difference software FLAC3 D is used in this paper.A CFG pile-gravel pile composite foundation model is established to simulate the coupling of fluid and dynamics,and the interaction between soil and structure.The anti-liquefaction performance,bearing capacity and stress of pile of composite foundation are discussed The main content of this article is:(1)The research progress and achievements of seismic liquefaction and multi-pile composite foundation are summarized and analyzed.The idea of establishing the model is introduced,the realization mode of soil-structure interaction and the key method of fluid and dynamic coupling are described.(2)A few-pile model of the CFG pile-gravel pile composite foundation is established.It is found that the liquefaction level in the middle of the liquefiable layer is the highest,the anti-liquefaction effect of the gravel pile is the best within the range of about 3 times of the pile diameter,and the multi-pile composite foundation has a better foundation treatment effect.(3)The peak acceleration of seismic wave,the imposed load and the length of gravel pile are taken as the influencing factors.With the increase of peak acceleration,the liquefaction level increases and develops deeper.The increase of the imposed load weakens the liquefaction level of the site,but the foundation settlement increases.The antiliquefaction performance of long gravel pile on deep foundation soil decreases with time,and two kinds of piles with long and short length can be used for staggered arrangement.(4)A pile group model of CFG pile-gravel pile composite foundation is established.The liquefaction resistance and bearing capacity are improved,and the outside action range of the gravel piles is increased to 5 times the pile diameter.The vertical stress of CFG side pile distributed along the direction of seismic wave acceleration is the largest after vibration.The maximum bending moment of CFG pile occurs at the boundary of soil layer,the property of soil layer has great influence on the distribution shape of pile bending moment.The seismic damage of composite foundation can be weakened by increasing the strength of gravel pile,increasing the strength of CFG pile or laying protective piles in the periphery of foundation.