Dynamic Response Of Pile Groups To Vertical Loadings Based On The Pile-soil Interaction

Pile foundation is widely used in soft soil layer as the support of various structures.In addition to the static load,many foundation and structure supported by pile foundation are affected by dynamic loads such as machine induced vibration,wave and earthquake.Different from the study of dynamic response of single pile,the study of vibration theory of pile group becomes more complicated due to the influence of pile group effect.At present,in the practical application of engineering,most pile foundations are in the form of group pile foundation.Therefore,it is of great theoretical significance and practical value to study the bearing mechanism and settlement calculation of pile groups under dynamic load and understand the interaction mechanism of pile soil pile.Based on the interaction between pile and soil,the dynamic response of rock socketed pile group and friction pile group under vertical excitation is studied in this paper.The main theoretical methods and achievements are as follows:(1)In view of the dynamic characteristics of rock socketed pile groups in homogeneous foundation under vertical load,an analytical calculation model of dynamic response of rock socketed pile groups under vertical load is established in this paper.Through the method of separating variables,the dynamic response of the soil around the pile is solved firstly,and the dynamic displacement of the pile foundation is expressed in different local coordinate system.Considering the pile-soil interaction,using Graf addition theorem to realize the transformation of local coordinate system of different piles,the analytical solution of displacement field of double piles is obtained,and finally it is extended to the vertical vibration analysis of pile groups.On the basis of verifying the correctness of this method,the parameter analysis is carried out.The results show that: the distance between two piles increases,and the interaction coefficient between piles decreases.The larger the slenderness ratio of pile is,the larger the interaction coefficient between two piles is.The greater the soil stiffness around the pile,the greater the interaction coefficient between the two piles.In pile group foundation,with the increase of pile spacing,the interaction coefficient between piles decreases gradually;the interaction coefficient of angle pile is the smallest,and that of middle pile is the largest.(2)In view of the dynamic characteristics of friction pile groups in homogeneous foundation under vertical load,this paper establishes an analytical calculation model for the dynamic response of friction pile groups under vertical load.Firstly,the dynamic balance equation of soil is established by wave theory,and the displacement expression of soil in local coordinate is solved by boundary condition.By using Graf addition theorem,the displacements in different coordinate systems are unified,and the expression of displacement field with unknown coefficient is obtained.The modulus function and density function are introduced to represent the elastic modulus and density of friction pile and virtual soil pile respectively,and the unified dynamic balance equation of pile and virtual soil pile is established.Combined with the condition of displacement continuity and stress coordination at the interface of pile and soil,the solution is carried out.The dimensionless parameter analysis shows that the interaction coefficient between piles is inversely proportional to the distance between piles and the ratio of pile diameter,and directly proportional to the ratio of pile-soil modulus.The dynamic stiffness of pile top is directly proportional to the distance between piles and the ratio of pile diameter,and inversely proportional to the modulus of pile-soil.The influence of the length depth ratio of pile to soil on the dynamic stiffness of pile top is weak.