Study On The Vertical Vibration Of The Pipe Pile In Saturated Soil Under Soil Plug Effect

In the southeastern coastal areas of China,due to the low topography and altitudes below 10 meters,most of them are plains formed by the impact of rivers.They are rich in water resources,have a high groundwater table,and are densely populated,with many urban distributions.With the urbanization process,The construction of a large number of building facilities such as houses,factories,highways,ports,airports,etc.was started.Due to the applicable conditions of pile foundations,it was adopted in large quantities in these areas.As a new type of pile,pipe pile has many advantages:(1)Due to the high bearing capacity of a single pile of pipe piles,in the same building foundation treatment,it is possible to select pipe piles with different pile diameters for combined design,and fully The bearing capacity of each pile is exerted;(2)Compared with solid piles,pipe piles have obvious advantages of low cost;(3)After the piles are piled,the quality is higher,and the length of the pile and the quality of the pile body can be easily detected.Since the 1960 s,pipe piles have been put into use in large quantities in the southeastern coastal areas of China.During the process of driving piles into the ground,it is inevitable that pile core plugs will pile up in the piles.Currently,for saturated soils,The effect of the medium-earth-plug effect on the longitudinal vibration characteristics of pipe piles is not particularly perfect.This paper takes the theoretical research as the main part,studies the influence relationship between pipe piles and soil plugs,and conducts indoor model tests and establishes ANSYS numerical model.Comparing the experimental results with the simulation results to verify the rationality of the theoretical calculations.This article expands on the following four points:(1)Based on saturated porous medium theory,vertical vibration of pipe pile with transversal inertia effect in homogeneous saturated soil was studied.The complex stiffness of the surrounding soil was obtained firstly with Novak’s layer method and saturated porous medium theory.Then the side wall shear force and inner wall shear force were obtained with the complex stiffness.The dynamic equations of pipe pile and soil was built by one-dimensional wave theory.Then,semi analytical solution of velocity response at top of pile in time domain and analytical solution of velocity response at top of pile in frequency domain were derived by the boundary condition and initial condition.And then,the influences of relevant parameters as density,wave and height of soil plug on admittance and velocity response at top of pile in time domain were analyzed.(2)Based on saturated porous medium theory,vertical vibration of pipe pile with transversal inertia effect in longitudinal layered saturated soil was studied.The complex stiffness of the surrounding soil was obtained firstly with Novak’s layer method and saturated porous medium theory.Then the side wall shear force and inner wall shear force were obtained with the complex stiffness.The dynamic equations of pipe pile and soil was built by one-dimensional wave theory.Then,semi analytical solution of velocity response at top of pile in time domain and analytical solution of velocity response at top of pile in frequency domain were derived by the boundary condition and initial condition.And then,the influences of relevant parameters as density,wave and height of soil plug on admittance and velocity response at top of pile in time domain were analyzed.(3)A low-strain pile foundation dynamic test was performed on the concrete model pipe piles prepared in-situ.From the perspective of the test,the influence of the soil plug height ratio on the time-domain response curve of the pile top velocity was verified.Combined with the pile-soil vibration model test,the theoretical results were obtained.The fitting analysis of the test results verified the rationality of the longitudinal vibration theory of pipe piles in saturated soil based on viscoelastic support.(4)The ANSYS finite element software was used to establish a numerical model for the coupling of surrounding soil,pipe piles and soil plugs.The longitudinal vibration characteristics of pipe piles and the vertical layered saturated soils in homogeneous soils were analyzed from the perspective of numerical calculation.Considering the soil plug effect,the vertical vibration characteristics of pipe piles.Then the influence of the height and density of soil plug on the time-domain curve of pile top velocity was studied.Combined with theoretical analysis,the feasibility of ANSYS finite element software was verified.