Theoretical And Simulation Research On The Response Characteristics Of The Reflected Wave In Small Strain Testing Of Pile Foundation

Pile foundation is a common basic form,which is of great significance to ensure the safety of construction structure.The quality testing of pile base is a very important link in the construction process of engineering.At present,low-strain reflective wave method has become one of the common pile-based detection methods,but the system uses theory and FLAC3D numerical simulation technology to analyze the characteristics of reflective wave curve is less research results.To this end,on the theoretical basis of the one-dimensional elastomer fluctuation equation,this paper first establishes the elastic pile-earth interaction model,deduces the settlement expression of the top speed of the pile,studies the influence law of different parameters on the time domain curve of the top speed of the pile,and summarizes the response characteristics of the reflected wave curve.Using FLAC3D numerical simulation,the velocity time domain curve of the complete pile and three single defect piles under the influence of different parameters is obtained,and the response characteristics of the reflective wave curve of the four types of piles are summarized.Finally,combined with the engineering case,the accuracy of the analytical solution and numerical solution analysis results is verified.The main results of the full text are as follows:(1)Based on the Darangbel solution of the one-dimensional wave equation,the system summarizes the characteristics of stress wave reflection and transmission,and summarizes the characteristics of the reflective wave curve of different types of piles.On this basis,the wave differential equation under the interaction of pile soil is established,the resolution solution expression of the top speed of the pile is derived by The Laplace transformation and Fourier transformation method,and the response characteristics of the reflected wave curve are summarized by analyzing the response characteristics of the top impact load,the elastic modulus of the pile body,the pile radius and the damping factor of the pile side on the attenuation of the stress velocity amplitude in the time domain curve.That is,with the increase of load,the amplitude of incident and reflection waves is increasing.With the increase of the elastic modulus of the pile,the amplitude of incident and reflection waves is decreasing.With the increase of pile radius,the amplitude of incident and reflection waves is decreasing.With the increasing damping factor on the side of the pile,the incident amplitude is unchanged,while the reflected amplitude is decreasing.(2)In view of the difficult problem of defect pile theory,FLAC3D is used to simulate the response characteristics of three single defect piles(expansion pile,shrink pile,separation pile)reflecting wave curve when defect position,defect size and defect thickness change,and the response characteristics of the reflected wave curve of the whole pile under the influence of different elastic modulus,impact load and local damping factor are simulated,namely:1)With the increase of the elastic modulus of the whole pile body,the amplitude of the incident wave decreases and the magnitude of the reflected wave increases.With the increase of impact load,the magnitude of incident and reflected waves increases.With the increase of pile damping factor,the incident amplitude decreases slightly and the magnitude of reflected wave decreases significantly,which is consistent with the result of theoretical solution.2)With the increase of the depth of the expansion pile expansion position,the amplitude of the expansion-diameter reflection decreases.With the increase of the area of the expansion diameter,the magnitude of the expansion reflected increases.With the increase of the thickness of the widening diameter,the amplitude of the expansion reflected increases.3)With the increase of the depth of the shrinkage pile shrink position,the reflected amplitude of the shrinkage site decreases.With the increase of shrinkage area,the shrinkage reflective wave decreases and the reflected wave amplitude of pile bottom increases.With the increase of shrink thickness,the magnitude of shrinkage reflection increases and the magnitude of pile bottom reflection decreases.4)With the increase of the depth of the dissociated pile separation position,the magnitude of the dissociation reflection decreases,and the magnitude of the reflection of the bottom of the pile increases slightly.With the increase of the area of the separation,the magnitude of the off-analysis reflection decreases,and the magnitude of the reflection of the bottom of the pile increases.With the increase of the thickness of the separation,the magnitude of the off-the-material reflection increases and the magnitude of the reflection of the pile bottom decreases.5)Comparing and analyzing the waveform curve of the shrinkage pile and the dissipated pile,we can see that the similarity is higher,but there are more sub-waves in the time domain curve of the separation pile reflection wave,and the reflected amplitude value of the discerning site is higher than the reflected amplitude value of the shrinkage site.(3)The on-site detection technology of low strain reflection wave method is summarized,and according to the four engineering pile model cases,the accuracy of the analytical solution and the numerical solution is verified by the complete model pile,and the accuracy of the numerical solution is verified by the expansion model pile and the segregation model pile,and finally the conclusion is that the analytical solution,the numerical solution and the measured pile results are more consistent.Figure 53 table 14 reference 96...