Changjie Zheng

Vertical Vibration of a Pipe Pile in Viscoelastic Soil Considering the Three-Dimensional Wave Effect of Soil

AbstractAn analytical solution is developed in this paper to investigate the vertical vibration of a pipe pile in viscoelastic soil. The soil is assumed to be a homogeneous and isotropic layer. The pipe pile is considered as a one-dimensional Euler rod. Considering both the vertical and radial displacements of the outer and inner soils and the soil pile–coupled vibration, the dynamic equilibrium equations of the soil and pile are established. The dilatations of the outer and inner soil are obtained by differential transformation on the equations of soil and the variable separation method. Then, the vertical and radial displacements of the outer and inner soils are obtained. The displacement response and impedance function of the pipe pile are derived using the continuity assumption of the displacement and stress between the piles and the soils. Numerical examples are presented to analyze the vibration characteristics of the pile.

Three-Dimensional Effects in Low-Strain Integrity Testing of Large Diameter Pipe Piles

AbstractThe interpretation of low-strain integrity testing performed on piles is commonly based on methods developed from the one-dimensional wave propagation theory. However, stress waves generated from the impact of the hammer on the head of a pipe pile propagate not only along the vertical, but also the circumferential and radial directions. One-dimensional methods that ignore these waves may underestimate the amplitude of the incident wave, and fail to predict the development of high-frequency interferences that may compromise the assessment of the integrity, particularly of large-diameter pipe piles. To account for these three-dimensional effects, the authors formulate a solution for determining the vertical vibration response along the cross-section of the pipe pile head to an impact load, which robustly accounts for coupling of pipe pile and viscoelastic soil vibrations. Presentation of the method is followed by a discussion on identifying the mechanisms that underlie body and surface stress-wave p...

Horizontal Vibration of a Large-Diameter Pipe Pile in Viscoelastic Soil

An analytical solution is developed in this paper to investigate the horizontal dynamic response of a large-diameter pipe pile in viscoelastic soil layer. Potential functions are applied to decouple the governing equations of the outer and inner soil. The analytical solutions of the outer and inner soil are obtained by the method of separation of variables. The horizontal dynamic response and complex dynamic stiffnesses of the pipe pile are then obtained based on the continuity conditions between the pile and the outer and inner soil. To verify the validity of the solution, the derived solution in this study is compared with an existing solution for a solid pile. Numerical examples are presented to analyze the vibration characteristics of the pile and illustrate the effects of major parameters on the stiffness and damping properties.

A Theoretical Analysis of the Vertical Shearing Mechanism of the H-Pile

Theoretical solutions dependent on vertical shearing mechanisms are derived by means of equilibrium analyses to calculate the effective vertical stress of the surrounding soil, the unit positive (or negative) shaft friction, and the axial force (or dragload) of the H-pile. They are calibrated by measured axial force and dragload of centrifuge model tests. In addition, the effects of vertical shearing on the load transfer mechanism of the H-pile are investigated.

Horizontal dynamic response of a large-diameter pipe pile considering the second-order effect of axial force

The second-order effect of axial force on horizontal vibrating characteristics of a large-diameter pipe pile is theoretically investigated. Governing equations of the pile-soil system are established based on elastodynamics. Three-dimensional wave equations of soil are decoupled through differential transformation and variable separation. Consequently, expressions of soil displacements and horizontal resistances can be obtained. An analytical solution of the pile is derived based on continuity conditions between the pile and soil, subsequently from which expressions of the complex impedances are deduced. Analyses are carried out to examine the second-order effect of axial force on the horizontal vibrating behavior of the pipe pile. Some conclusions can be summarized as follows: stiffness and damping factors are decreased with the application of axial force on the pile head; distributions of the pile horizontal displacement and rotation angle are regenerated due to the second-order effect of the applied axial force; and redistributions of the bending moment and shearing force occur due to the second-order effect of the applied axial force.

Model tests on XCC-piled embankment under dynamic train load of high-speed railways

Piled embankments, which offer many advantages, are increasingly popular in construction of high-speed railways in China. Although the performance of piled embankment under static loading is well-known, the behavior under the dynamic train load of a high-speed railway is not yet understood. In light of this, a heavily instrumented piled embankment model was set up, and a model test was carried out, in which a servo-hydraulic actuator outputting M-shaped waves was adopted to simulate the process of a running train. Earth pressure, settlement, strain in the geogrid and pile and excess pore water pressure were measured. The results show that the soil arching height under the dynamic train load of a high-speed railway is shorter than under static loading. The growth trend for accumulated settlement slowed down after long-term vibration although there was still a tendency for it to increase. Accumulated geogrid strain has an increasing tendency after long-term vibration. The closer the embankment edge, the greater the geogrid strain over the subsoil. Strains in the pile were smaller under dynamic train loads, and their distribution was different from that under static loading. At the same elevation, excess pore water pressure under the track slab was greater than that under the embankment shoulder.

Resistance of Inner Soil to the Horizontal Vibration of Pipe Piles

AbstractThe resistance of the soil inside a pipe-pile’s cavity to the horizontal dynamic response of the pipe pile is quantified by extending a well-established analytical model from the literature...

Study on the Vibration of Geosynthetic Reinforced Cushion in Pile Supported Embankment

The vibration of geosynthetic-reinforced cushion in pile supported embankment due to high-speed train load is theoretically investigated in this paper. The cushion is considered as an elastic sheet on viscoelastic foundation. The high-speed train load is assumed as a dynamic load made up of a stationary load and three sinusoidal loads. An analytical solution of the vibration response of cushion due to high-speed train load is obtained. Numerical examples are given to analyze the vibration characteristics of cushion and the effect of the train speed, Young’s modulus and thickness of cushion on the displacement response. The results show that the displacement response of cushion increases as the train speed increases. The peak value of displacement increase steeply with the decrease of damping. Furthermore, the influence of high-frequency load on the displacement decreases with the increase of the train load and damping. Properly increasing the Young’s modulus and thickness of cushion can effectively reduce the displacement of cushion.