Analysis Of Vibration Characteristics Of Pile Foundation In Layered Liquefiable Soil

As an important foundation,pile has been widely used in all kinds of building structure with good capacity and seismic performance.Under the seismic force,especially in easily liquefied soils,the continuous accident of the pile destruction make the promotion of the research and development of the pile failure mechanism in liquefied field.The carrying capacity of a pile under dynamic load is related to its mechanical performance,and the mechanical performance of the pile is mainly reflected in the dynamic properties of the pile foundation.Therefore,the study on the dynamic properties of piles in liquefied soils is the key issue for analysing the dynamic interaction of pile-soil.In recent years,the research on the dynamic properties of piles is researched extensively at home and abroad,and certain progress has been achieved.With the wide use of the pile foundation,especially in some countries of earthquakes,the problems of vibration properties of piles are brought to the attention of the scholars and experts.So the study of pile-soil interaction and vibration characteristics of the pile in liquefied soils is of great engineering significance and theoretical value.In this thesis,according to the characteristics of liquefiable soil in earthquake,the soil profile is composed of a non-liquefied crust layer at the ground surface,a liquefied layer in the middle of the soil and a non-liquefied base layer.Based on the dynamic Winkler model for the pile-soil interaction and Novak's thin layer theory,the equations of vertical and horizontal vibration of a single pile in liquefied soils is established,and the vertical and horizontal dynamic impedance of soil layer is obtained further.The present method is verified to be applicable and efficient by comparing with the existing results;The study of dynamic impedance and response of single pile is extended to pile groups in liquefied soils.With the principle of superposition based on dynamic interaction factors,the horizontal,rocking and horizontal-rocking dynamic response of pile groups in liquefied soil is analyzed,and a parametric study is conducted to analyze the effect of the liquefaction degree,liquefied soil thickness,pile-soil modulus ratio and the ratio of pile spacing and diameter on the horizontal,rocking and horizontal-rocking dynamical stiffness and damping;the influences of the number of piles on dynamic impedance is investigated by comparing with the vibration stiffness and damping factor of 2×2,3×3 and 4×4 pile group.The application scope of the vibration impedance calculation of pile groups is extended,and a theoretical basis for the vibration analysis of pile groups in liquefied soils is provided.The calculation results show that,the liquefaction degree,liquefied soil thickness,pile-soil modulus ratio and the slenderness ratio of the pile have a more significant influence on the vibration stiffness factor of single pile and pile groups,but have little effect on damping;The characteristic of horizontal vibration of pile in liquefied soil is closely related to axial force,and the effect of the dynamic impedance is weakened under axial force;The ratio of pile spacing and diameter has influence on the vibration characteristic of pile groups,and the pile-group effect will attenuate with the increscent ratio of pile spacing and diameter between piles;The horizontal,rocking and horizontal-rocking dynamic impedance of pile groups are reinforcing with the increase of group pile number,and a consistent volatility is maintained.Moreover,the dynamic response of pile groups is characterized by pile number,pile-soil properties,pile spacing and so on,instead of the simple superposition of dynamic impedance of the single pile.