This study used the 2D boundary element method in time domain to examine the screening effectiveness of open trenches on reducing vibration generated by a high-speed train. The parameters included configurations of the trench, train speed, the distance between the source and the trench, and the Poisson’s ratio of the soil. A reducing displacement level (in dB scale) was defined and used to evaluate the screening effectiveness of a wave barrier. The maximal reducing displacement level reached 25？dB when an open trench was used as a wave barrier. The depth of an open trench is a main influential parameter of screening effectiveness. The cutoff frequency of the displacement spectrum increases with decreasing trench depth. The maximal screening effectiveness occurs when the depth is 0.3-0.4 Rayleigh wavelength. Using an open trench as a wave barrier can reduce 10–25？dB of vibration amplitude at frequencies between 30 and 70？Hz. A considerable increase in screening effectiveness of the open trench was observed from 30 to 70？Hz, which matches the main frequencies of vibration induced by Taiwan High Speed Rail. The influence of trench width on screening effectiveness is nonsignificant except for frequencies from 30 to 40？Hz. Poisson’s ratio has various effects on the reduction of vibration at frequencies higher than 30？Hz. 1. Introduction High-speed trains (HSTs) have played an essential role in intercity transportation during the past decades. The weight of freight trains and the speed of passenger trains have increased. Trains passing populated areas result in ground vibration and cause disturbances to adjacent structures. Reducing vibration in nearby structures has become a crucial issue in practice. Installation of barriers (such as a row of concrete piles or steel pipe piles and open trench or infilled trench) between tracks and the structures is one solution of isolation vibration. An open trench is often used as a wave barrier causing reflection, scattering, and diffraction effects. The vibration amplitude is thus reduced on the ground surface behind the open trench. Elastomer or rubber between the ballast and subgrade, soil improvement underneath the track, and floating slab track are other effective methods to reduce vibration induced by train. A number of experimental and numerical studies [1–4] have been conducted to examine the ground vibration induced by HSTs. These studies mainly focused on the ground vibration generated by HSTs. In addition, the screening effectiveness of trenches on harmonic vibration sources generated by machine foundations
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