Abstract: The dynamic equations for the horizontal vibration of outer soil and inner soil of pipe pile are developed with considering the layered characteristics of soil. The stiffness and damping coefficients of pipe pile-soil dynamic interaction are obtained using potential function, boundary conditions and parity of the radial and circumferential displacements of outer soil and inner soil. The soil is simulated as a continuous-distribution spring-damper, and a horizontal vibration equation of the pipe pile is developed under the forces of outer soil and inner soil. The horizontal vibration is solved by the initial parameter method and the transfer-matrix method, and the dynamic horizontal impedance of pipe pile at pile head is obtained. The influences of shear modulus of soil layer, pipe pile wall thickness, outer and inner soil shear modulus ratio and thickness of soil layer on the dynamic impedance of pipe pile are obtained through numerical analysis. It is found that within the range of low frequency, the horizontal vibration of pipe pile in layered soils is mainly affected by the shear modulus of soil layer, pipe pile wall thickness and outer and inner soil shear modulus ratio, while the lateral vibration of pipe pile is influenced by the thickness of soil layer in a wide frequency range. As the thickness of the pipe pile wall and the shear modulus of soil around the pile increase, the absolute value of the lateral dynamic impedance of pipe pile increases.

Key words: layered soil, horizontal vibration, pipe pile, transfer-matrix formulation