Study on Vertical Vibration of Partially Exposed Friction Pipe Pile Groups Based on Fictitious Soil Pipe Pile Model

Regarding soil below the pipe pile as fictitious soil pipe pile, the vertical dynamic model of partially exposed friction pipe pile is established. Winkler spring-damper model is used to simulate the vertical dynamic interaction between soil around the pile and pipe pile, and between pile core soil and pipe pile by ignoring the radial displacement and circumferential displacement of soil. Considering the displacement boundary conditions of the soil around pile and pile core soil, the effects of the soil around pile and pile core soil on the pipe pile are obtained, and the complex stiffness of vertical vibration of a partially exposed friction pipe pile is obtained by using the initial parameter method and the transfer matrix method. The vertical dynamic interaction factor of partially exposed friction pipe pile-pipe pile is obtained by considering the dynamic interaction between pipe pile and pipe pile. Based on the principle of pile groups superposition and the vertical dynamic interaction factor of pipe pipe-pipe pile, the vertical vibration of partially exposed friction pipe pile groups is studied, and the vertical dynamic impedance of pipe pile groups is also obtained, and the influences of relevant parameters on the vertical dynamic impedance of partially exposed friction pipe pile groups are investigated by numerical examples of 3 x 3 pipe pile groups. The results show that the dynamic stiffness and damping of end-bearing friction pipe pile groups are larger than friction pipe pile groups, and the change of peak values of curves varying with frequency are gentler. The restraint effect of bedrock under pipe pile can increase the vertical dynamic impedance of pipe pile groups. Increasing the length of pipe pile is beneficial to increase the vertical dynamic impedance of pipe pile groups. The larger the pipe pile spacing, the sharper the peak values of curves of the dynamic stiffness and damping curves of pipe pile groups varying with frequency. The influence of pipe pile geometry on vertical vibration of pipe pile groups is greater than that of physical properties such as elastic modulus of pipe pile and shear modulus of soil.