Experimental Study on Influencing Factors of Pile Length Detected by Parallel Seismic Method

This paper focuses on the field implementation of the parallel seismic method (the PS method) to detect the length of existing piles. Depending on a municipal bridge project, the in-situ tests of pile foundation are carried out focusing on the influence of pile top excitation mode, rock-socketed condition at pile tip, and superstructure on the waveform of the PS method. The test results show that when the top of the pile foundation is free, the seismic waveform obtained by vertical and horizontal tapping is generally consistent, and the attenuation of the first break amplitude increases with the increase of pile to borehole distance. The farther the test borehole is from the pile edge, the more significant the soil heterogeneity affects the first break arrival time fitting line shape. It is difficult to determine the buried depth of the pile by fitting the straight-line method because the wave velocity in the pile section is close to that in the bearing bedrock layer at the pile tip, and the pile tip is embedded in the complete bedrock. However, it can be preliminarily judged whether the pile tip enters the bedrock and the bonding quality between the pile tip and the bedrock by analyzing the geological condition and construction technology. The energy of the first shear waves generated by tapping the side of the bridge pier with different angles decays rapidly for the existing bridge piles with the superstructure. The P-wave component in the seismic wave will increase by tapping the side of the pier obliquely with the auxiliary device, which can significantly improve the signal quality of the PS method.