Application Of Parallel Seismic Method To Detect Existing Pile Foundations Of Buildings

The exposures and damage incidents of pile foundations have occurred in recent years,underground rail transit construction through old buildings is increasing,and the reinforcement and reconstruction of old buildings is also gradually emerging,the integrity and length testing of existing pile foundations becomes especially important.The low strain reflection wave method is currently widely used in detecting the integrity and length of pile foundation,but due to factors such as the cap and the superstructure,it is not suitable for existing pile foundations.Parallel seismic method has broad application prospects in the detection of existing pile foundations,but related research is relatively lagging.Based on stress wave theory,this paper studies the application of parallel seismic method to detect the existing pile foundations by using numerical simulations and field measurements.The main works are shown as below:(1)The parallel seismic method based on the first wave amplitude of the stress wave is proposed in this paper.The piles detection process by parallel seismic method is simulated,and the numerical simulation method is verified by comparing theoretical value,calculated value and simulated result.defect length,the buried depth of pile and defect,the amplitudes and widths of impulse,damped soil is discussed.(2)The detection process by parallel seismic method for segregated,diameter-expanding,diameter-shrinking piles is simulated,considering the elastic moduli of segregated part,borehole distance,the radius of full-axisymmetric defect,the size and positions effect of local defect,analysis results difference of traditional method based on the propagation velocity of the stress wave and method which proposed in this paper and based on the first wave amplitude of the stress wave are compared.(3)For the special case of hole located on the pile,the detection process by parallel seismic method for segregated,diameter-expanding,diameter-shrinking piles is simulated,considering the elastic moduli of segregated part,borehole distance,the radius of full-axisymmetric defect,the size and positions effect of local defect,analysis results difference of traditional method based on the propagation velocity of the stress wave and method which proposed in this paper and based on the first wave amplitude of the stress wave are compared.(4)Based on the measured data about the existing pile testing assessment,the superiority of the parallel seismic method proposed in this paper is verified,improvements on equipment and method for on-site testing are proposed.