Key Problems Investigation On Non-destructive Integrity Detection Of Piles With Elevated-cap(Beam)

Low-stain reflected wave method,known for its simplicity,cost-effective and time-saving,has been widely adopted in pile integrity testing.However,the related research is far from perfect as the influence of the control elements of the defect(the longitudinal length,radial extent,location)on the detection results and their interactions have not been systematically investigated.On the other hand,the integrity detection of the piles with elevated-cap(beam)becomes an urgent problem to be solved because of the possible damage caused by the natural or man-made disasters and environmental collisions,while the existing detection methods are not satisfactory.In light of this,the influence of the control elements of the defect on the dynamic response of pile is investigated systematically based on the pile vibration theory,and on this basis a new non-destructive method for integrity testing of piles with elevated-cap(beam)is proposed.The principal researches are as follows:1.The influence of defect dimensions,namely the longitudinal length and radial extent(or the decrease of the modulus)of the defect,on the low-strain reflected wave signals and its relationship with the defect location and pile-soil parameters are investigated.On this basis,the defect located in the midpoint of the pile length is taken for example to discuss the superposition effect caused by the long defect and the identifiability of the short defect and their relationship with the pile-soil parameters and the impulse width.2.By utilizing the shear complex stiffness transfer method to simulate the radial inhomogeneity of soil caused by the construction disturbance effect and the transverse inertia effect to consider the three-dimensional effect of wave propagation,the analytical solution in the frequency domain and the corresponding semi-analytical solution in the time domain for the dynamic response of a large diameter pile are obtained.Based on the solutions,the influence of the defect on the low-strain reflected wave signals of the large diameter pile,as well as its relationship with the transverse inertia effect,pile parameters and the radial inhomogeneity of soil caused by the construction disturbance effect is investigated.Finally,the reliability of the mathematical model is verified by comparing with the in-situ test results.3.Universal frequency response function method based on traveling wave decomposition is put forward aiming at the limitation of the existing methods in nondestructive testing and assessment of post-disaster tall platform pile foundation.The reaction acting on the pile top by the superstructure is simplified as the viscoelastic supporting boundary and the wave equation analysis program is used to calculate the universal frequency response function at the test section.Information contained in the universal frequency function is switched from frequency domain to time domain by importing virtual half-sine pulse at the test section.Then,the reliability of the detection method is demonstrated theoretically.Finally,a parametric study is conducted to investigate the influence of pile-soil parameters and the control elements of the defect on the universal frequency response function as well as the time domain response transformed from it.4.Based on the three-dimensional axisymmetric model which can consider the radial inhomogeneity of soil and the Timoshenko beam theory,together with the boundary conditions at the pile-beam interface,the velocity-time curve and the force-time curve at the test section are obtained.By means of the Fourier transform and the calculation method given in chapter 3,the velocity admittance and the time domain response at the test section are obtained,and are adopted in the detection of the single-row pile group with elevated-cap.The influence of the defect,pile-soil parameters and the construction disturbance effect is analyzed.Finally,the applicability of the proposed method to the integrity testing of the in-service large diameter pile is discussed.5.Using a three-dimensional axisymmetric model,the frequency-domain analytical solution and the time-domain semi-analytical solution for the dynamic response of a large-diameter pipe pile are derived considering the layered properties and radial inhomogeneity of the outer and inner soil.Based on the solutions,the influence of the inner soil on the dynamic response of the pile is analyzed.Then,the influence of the defect and its relationship with the inner soil as well as the radial inhomogeneity of soil is investigated.Finally,the dynamic response and integrity detection of the in-service large diameter pipe pile are discussed.The present work is of theoretical significance and application prospect in integrity detection of the newly installed single piles as well as the in-service piles with elevated-cap(beam).