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Received Feb 17, 2018; Accepted Apr 1, 2018
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1. Introduction
Urban rail transit has alleviated the great traffic pressure induced by accelerated urbanization [1]. The vibrations caused by train operation are transmitted from the rail to the track bed, tunnel wall, and surrounding rock. This influences the surrounding environment [2], especially in vibration-sensitive areas such as hospitals, schools, precision instrument laboratories, residential buildings, and ancient buildings [3].
Research is actively ongoing worldwide to decrease the effects of vibration caused by subway operation, and various measures have been applied to the construction of subway lines. Hui and Ng [4] measured in situ rail viaduct vibrations and demonstrated that concrete floating slab track can reduce the vibration level by more than 30 dB within a frequency range of 63–200 Hz. Miwa et al. [5], Kim and Youn [6], and Hussein and Hunt [7] also found that the floating slab track can effectively reduce the vibration caused by train. Costa et al. [8] put forward that placing a ballast mat beneath the subballast can considerably reduce the free-field vibrations at frequencies above 40 Hz by up to 20 dB. Similarly, Xin and Gao [9] and Xu et al. [10] concluded that a mat slab layered under the track can reduce vibrations within bridges and tunnels. Xia et al. [11] established a numerical model representing the train-track-viaduct system and studied the dynamic responses of an elevated bridge with the ladder sleeper track. Their results showed that the ladder sleeper track also has a very good vibration mitigation effect. Many other vibration reduction measures have been also applied in China and abroad, such as high-resilience fastening systems [12], labyrinth constrained damped rails [13], sleeper cushions [14], shock absorber fasteners [15], and the floating ladder sleeper track [16].
The Long Elastic Sleeper Track (LEST) is a new type of vibration reduction track based on the Low Vibration Track (LVT). It has gradually been applied to urban rail transit in recent years because it is economical and overcomes the defects of LVT with an obvious advantage in terms of medium vibration reduction demands. Furthermore, LEST...