Surface-wave attenuation by periodic pile barriers in layered soils

Ground vibrations caused by locomotive trains and heavy machinery and equipment have a negative impact on the adjacent facilities if not properly controlled. Normally, these vibrations propagate in form of surface and body waves. To this end, the need to minimize the effects of ground waves have attracted significant attention of researchers.

Presently, several approaches have been made to reduce the effect of ground waves. For instance, wave barriers such as sheet pile walls and in-filled trenches have been installed to reduce the unwanted ground vibrations by diffracting the surface waves. Unfortunately, trenches are unsuitable for high water table regions and soft grounds. The problem has been subsequently solved by using pile barriers for vibration isolation because they can cover high depths and arranged in a desirable configuration. Consequently, it has enabled study of isolation barrier both numerically and experimentally. Recently, interest in wave barriers made of multi-rows of piles has increased. However, the dispersion properties of surface waves in rows of piles have not been fully explored. Also, time domain analysis and amplitude reduction spectra are still lacking.

In fact, multi-rows of piles can be considered as a typical periodic structure in space. The band theory in solid-state physics shows that periodic structures possess band gaps, or termed as attenuation zones. Incident waves with frequency in attenuation zones cannot propagate through the periodic system. Based on this novel feature, Xingbo Pu and Zhifei Shi at Beijing Jiaotong University investigated the surface-wave screening based on the periodic pile barriers taking the attenuation zones into consideration. They examined the effects of different parameters such as the pile spacing, pile length, pile radius and pile location. The responses were conducted both in time and frequency domains. Eventually, the dispersion relations and attenuation zones for surface waves in a periodic pile and layered soil system were determined by finite element method in three-dimensional contexts. Their work is published in the research journal, Construction and Building Materials.

The authors observed that multi-rows of piles can be reduced to a unit cell on periodic theory. Among the parameters that affected the attenuation zones of periodic pile barriers, pile spacing was a key consideration. For instance, its increase resulted in a corresponding low-frequency range of the surface wave attenuation zone. Consequently, an increase in the pile radius resulted in the widening of the attenuation zones. As predicted by the periodic theory, the authors observed that the incident surface wave is well reduced in attenuation zones.

According to the authors, attenuation zones can be used to optimize the design parameters of the pile barriers. Therefore, the study opens up new horizons for row piles and thus will advance the design of periodic piles as wave barriers. Furthermore, it will ensure reduced unnecessary ground vibrations.