Theoretical And Practical Study On Space Axisymmetric Problem For Low Strain Dynamic Testing Of Pile

The stress-wave propagation in a pile is mainly studied. First, a 3D (axisymmetric) computing model for transient vibration of soil-pile system is presented based on elastic theory. Then the dynamic response of an intact pile impacted by transient axial impulse is computed with finite difference method, and the difference between 3D (axisymmetric) and ID axial velocity responses at the pile top have been compared and analyzed. The wave snapshots at different time, which give a visual interpretation of propagation of wave in the pile, are obtained. The response of an intact pile with a typical defect has been studied. 3D effect is analyzed and the average velocity of wave propagating in the pile, which mainly influences inverse interpretation, is discussed. Finally, the theory results are verified by model experiment. It is shown that 3D results have the same phase with ID results. The pile radius, the duration of impulse, the ratio of hammer radius to pile radius and shear velocity of the soil around the pile have influences on 3D effect. The best position of receiver is 0.55R from the pile center. The average velocity of wave propagating in the pile reduces due to transversal inertia effect and 3D effect. The precision of inversion depends on the properties of defect and the impulse condition. The theory results are verified by model experiment.