Elementary experimental investigation of the periodic piles for vibration isolation of design frequency range

The current research on the periodic piles for vibration isolation based on the method of band gap mainly focused on theoretical and numerical analysis. In this paper, the method of principle experiment was adopted to validate the characteristics of attenuation zone of the periodic piles for vibration isolation. Four experimental cases were designed to consider two types of periodic piles (i.e., hollow steel piles and periodic hollow steel piles filled with soil) and two types of periodic layout (i.e., a hexagonal configuration and a square configuration). With the excitation of impulsive loads, the experimental cases with vibration isolation measures were compared to those without vibration isolation measures. Vibration attenuations of the periodic piles in various experimental cases were measured, analyzed and compared with theoretical band gaps. The measured vibration response in various experimental cases was greatly attenuated within the band gaps of theoretical calculations. The levels of attenuation were above 50% and the highest one was up to 98%. Both the attenuation effect and vibration isolation performance were greatly achieved, and thus the effectiveness of theoretical analysis is verified. The horizontal level of vibration attenuation of the periodic piles is better than the vertical. From this trend, with the same conditions, the vibration attenuation level of periodic piles in a hexagonal configuration was better than those in a square configuration. Moreover, soil-filling could effectively increase the width of the initial band gap and the attenuation zone of periodic steel pipe piles arranged in a hexagonal configuration, but reduce the lower bound frequency of the initial band gap and the attenuation zone of periodic steel pipe piles arranged in a square configuration. By analysing the band gap of periodic piles that were approximate to actual engineering dimensions corresponding to the periodic piles in the experimental cases, it is found that there are several band gaps appearing in the frequency range of 0-80 Hz which can be lower than 20 Hz. This study further illustrates that an objective frequency range can be designed to be isolated by periodic piles, and the periodic piles based on band gap theory can have a broad application prospect in the vibration isolation induced by metro train.