Influence Of Soil Around Pile On Stress Wave Transmission And Defect Identification Of Pile Body

The pile foundation is widely used in Civil Engineering because of its advantages of large bearing capacity and high strength.However,the pile foundation is concealed work,and its quality is often affected by construction level,geological conditions and other factors,thus reducing the quality of the whole pile foundation project.Therefore,the integrity of foundation pile must be tested.The most common detection method for pile integrity is the stress wave reflection method,which is widely used because of its simplicity and speed,but it often cannot be judged due to the influence of soil resistance around the pile.Therefore,based on the stress wave theory,this paper studied the influence of soil around pile on stress wave transmission and defect identification of pile body through theoretical analysis,model test and numerical simulation.The main research contents and results are as follows:(1)According to the dynamic theory,the governing equation of foundation pile considering the action of soil around the pile is established,and the analytical solution of velocity response of any section of pile is obtained by wave theory.(2)By assuming the half-sine or ascending cosine incident wave,it is concluded that the soil resistance around the pile will cause negative vibration of the particle at the pile top,leading to negative pulse after the first wave of the velocity signal,and with the increase of the pulse width,the negative pulse phenomenon gradually weaken.(3)According to the attenuation law of stress wave transmission along the pile and the reflection law of impedance section change,the quantitative analysis relation of defect degree of single defect pile and multi-defect pile is established,which can be used to quantitatively identify the defect degree of the pile.(4)According to the test results of model piles at different ages,it is concluded that with the increase of ages,the soil damping around piles gradually increases,and the ratio of reflected wave amplitude to incident wave amplitude decreases gradually,which verifies the correctness of the quantitative identification method of foundation pile defects.(5)Using the numerical simulation of pile extends the soil parameter change on the influence of the stress wave transfer law,it is concluded that the pile soil damping is the main factor of the stress wave attenuation,which under the effect of the pile soil damping,the damping coefficient of stress wave attenuation basically do not produce quality influence,the attenuation of stress wave caused mainly stiffness damping coefficient.(6)For the defective pile,the larger the defect degree and the axial size are,the larger the reflected wave amplitude of the defect is,and the smaller the reflected wave amplitude of the pile bottom is.In different defect degrees,the axial size of the defect has different effects on stress wave attenuation.For piles with multiple defects,the upper defects have an effect on the lower defects,while the lower defects have no effect on the upper defects.