Research On Horizontal Dynamic Interaction Between Pipe Pile And Saturated Soil

With the rapid development of pile foundation in my country’s construction field in recent years.Large-diameter pipe piles are widely used in southeast coastal areas and offshore facilities due to their outstanding performance,simple construction process,high single pile bearing capacity,high bending and crack resistance,good durability,concrete saving,and economic benefits.In the southeast coastal area,the water level is high and the soil is mainly saturated soil,so the influence of saturated soil parameters on pile bearing capacity should be considered in the calculation process.Under the action of horizontal dynamic load,the pipe pile in saturated soil is not only affected by the resistance of the pile side soil,but also by the resistance of the core soil for the pipe pile with large inner diameter.Therefore,the force composition of large-diameter pipe piles and small-diameter pipe piles is different.In the model calculation process of small-diameter pipe piles under the action of horizontal loads,only the effect of the side soil of the piles needs to be considered.In the process of model calculation of large-diameter pipe piles,both the pile side soil and the pile core soil need to work together.The resistance of the pile side and the core of the saturated soil is not only related to the length of the pile and the inner diameter of the pipe pile,but also to the porosity,compressibility,permeability and liquid modulus of the saturated soil.Therefore,it is of great significance to study the interaction of pile side soil,pile core soil and pipe pile,and the dynamic response of the joint coupling of pile side soil,large diameter pipe pile and pile core soil.In addition,it is necessary to propose a simplified calculation method for designers to refer to solve the pile foundation dynamic problem.Based on field tests of single piles and pile groups,combined with theoretical analysis,the pile head stiffness,interaction factor and soil displacement of small-diameter pipe piles,large-diameter pipe piles,small-diameter group pipe piles and largediameter group pipe piles are studied.The main work and research results are as follows:(1)In order to analyze the dynamic interaction relationship of pile groups,single-pile,two-pile,three-pile and four-pile dynamic tests were carried out,and the curves of acceleration and displacement amplitude of pile head with time and frequency were obtained.The pile head stiffness of the single pile and the pile group is calculated by the displacement amplitude curve combined with the "Testing Specification for Dynamic Characteristics of Ground"(GB/T50269-2015),and the pile head stiffness of the single pile and the pile group is given.Based on the pile head stiffness of single pile and pile group,the calculation formula of dynamic efficiency coefficient of pile group is given.(2)In order to obtain a simplified calculation method of the horizontal dynamic stiffness of single pile and pile group in multi-layer soil under horizontal load,a simplified calculation model of horizontal pile head dynamic stiffness of single pile and pile group in multi-layer soil is established.The calculation formula of pile head stiffness of single pile and pile group is given by formula derivation,and the simplified analytical solution expressions of pile group interaction factor and pile group dynamic efficiency coefficient are obtained through calculation.The results obtained from the field test in Chapter 2 are compared with the calculation results obtained from the simplified model to verify the correctness of the calculation model.The variation law of the stiffness of the single pile head,the pile head stiffness of the pile group,the interaction factor of the pile group and the dynamic efficiency coefficient of the pile group with the frequency,the distance between the piles,the direction of horizontal vibration and the angleθ between the connecting lines of the two piles is analyzed.(3)In order to study the soil resistance of the pile under the horizontal load of the pile side and the pile core saturated soil,based on the Biot poroelasticity theory,the Helmholtz decomposition method and the separation variable method were used to obtain the saturated soil dynamic control equation.Combined with the boundary conditions of the pile side soil and the pile core soil,the analytical solutions of the displacement and stress of the pile side soil and the pile core soil under the horizontal load are obtained,and then the soil resistance expressions of the pile side soil and the pile core soil are obtained.Numerical examples are used to analyze the influence of the porosity,compressibility,permeability,liquid density and liquid modulus of saturated soil on the resistance coefficient of pile side soil and pile core soil with the change of frequency.The influence of saturated soil parameters on the resistance of pile core soil with the change of inner diameter is studied.(4)In order to study the dynamic response of small-diameter pipe piles and largediameter pipe piles in saturated soil under horizontal load,based on the mathematical model of the saturated soil resistance of the horizontal vibration pile on the pile side and the core of the pile proposed in Chapter 4,the coupling relationship between the pile and the saturated soil is considered.The calculation models of pile side saturated soil-small diameter pipe pile,pile side soil-large diameter pipe pile-pile core soil are established,and then the analytical solutions of the horizontal pile head stiffness of small diameter pipe pile and large diameter pipe pile are obtained.The results obtained in this chapter are compared with the existing calculation model and the single pile stiffness of the pipe pile obtained by the test in Chapter 2 through numerical examples to verify the correctness of the proposed calculation model.The variation law of shear stiffness,flexural-shear stiffness and bending with saturated soil parameters porosity,compressibility and void liquid bulk modulus under the action of horizontal dynamic loads for small and large diameter pipe piles was analyzed.(5)In order to study the dynamic response of small-diameter group pipe piles and largediameter group pipe piles in saturated soil under horizontal load,based on the expression of the resistance of the pile side saturated soil and the expression of the pile core soil resistance given in Chapter 4,a computational model for a small diameter pipe piles and large diameter groups of pipe piles.The expressions of the horizontal pile head stiffness,pile group interaction factor and soil displacement attenuation function of small-diameter group pipe piles and largediameter group pipe piles in saturated soil are obtained through formula derivation.The results obtained in this chapter are compared with the existing calculation model and the pile head stiffness obtained from the test in Chapter 2 through numerical examples to verify the correctness of the proposed calculation model.The influence law of the parameters of saturated soil,pile spacing and pile diameter on the horizontal stiffness of pile head,soil displacement attenuation function of pile side and pile group interaction factor of group pipe piles and largediameter pile group piles in saturated soil is studied.The effects of considering pile core soil and not considering pile core soil on the horizontal stiffness of pile head,pile side soil displacement attenuation function and pile group interaction factor of large-diameter pipe piles are considered.