| The technology of low-strain reflected wave measuring pile is widely used in the pile test engineering because of its simple operation and low price.However,due to the three-dimensional effect of the measured wave and the soil around the pile,the test results needs to be improved and often needs to be supplemented by other means.Therefore,in order to improve the accuracy of pile measurement by low-strain reflection wave method,it is necessary to use the numerical simulation and field measurement experiment on the basis of theoretical analysis to comprehensively learn the propagation characteristics of stress wave in the pile body,and the influencing factors and laws of attenuation.The main contents are as follows:(1)Introducing the one-dimensional stress wave theory,and using software to carry out numerical simulation,analyzing the vibration propagation process,the three-dimensional effect of stress wave and its influencing factors,and the dispersion effect in the process of stress wave propagation.It is concluded that the three-dimensional effect of stress wave is related to the ratio of wavelength to pile diameter,and the three-dimensional effect is more obvious with the decrease of ratio.With the increase of pulse excitation surface,the effect of three-dimensional effect is more serious.The signal receiving point is tested to find the position where the reflected wave of the particle is least affected by the three-dimensional effect.(2)The propagation characteristics of stress waves in intact piles and defective piles are studied.It is proved that the relationship between the amplitude of the reflected reflection wave and the relative change of the wave impedance at the defect is close to the one-dimensional stress wave theory.(3)The attenuation effect of soil around the pile on the stress wave propagation is analyzed;The influence of the surrounding soil of the layered pile on the stress wave propagation is studied,and the characteristics of the reflected wave caused by the change of the wave impedance of the soil and the defect of the pile body is obtained.Besides,the example of the wave impedance transition section of the pile body with the stratificationof the soil around the pile is compared,it cannot be found that the difference between the two situation.(4)Using numerical simulation,the attenuation factors of the pile body stress wave are obtained,including the pile diameter,the pile body wave velocity,the soil parameters around the pile,and the pulse width.The law of attenuation is discussed.The results show that the attenuation rate increases with the shear wave velocity of the pile and the attenuation rate increases with the increase of the shear wave velocity of the soil around the pile.Changing the Poisson's ratio of the soil,the stress wave attenuation rate hardly changes.(5)Using the field test to verify the relevant content of the numerical simulation part,the results show that the stress wave will reflect at the position of the wave impedance change in the pile,and the surrounding soil of the pile will change the phase and amplitude of the reflected wave,corresponding to different soils,The stress wave attenuation rate is different,and the stress wave propagation characteristics of the soil around the pile are consistent with the change of the pile wave impedance.In this paper,the numerical simulation analysis is combined with the field model experiment.The propagation characteristics of the stress wave in the pile and the defect pile are analyzed from the perspective of excitation,propagation and reception of the stress wave.Combined with the surrounding soil environment,from the amplitude and phase offset of the signal received at the top of the pile,the attenuation rate of the longitudinal vibration velocity of the pile body,and the stress wave characteristics corresponding to the layering of the soil reveal that the soil around the pile propagates the stress wave in the influence law of the broadcast characteristics. |
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