Vibration transfer from slab tracks on piled foundations

Abstract

Railway tracks on soft soil are often supported by a piled foundation to increase track stiffness and reduce track deformation and settlement. In this paper, we consider the case of a slab track on a piled foundation and a floating slab track on a piled foundation, and compare their vibration transfer to the free field with the case of a slab track and a floating slab track. The case of a floating slab track on a piled foundation is inspired by the design of a new light railway line on very soft soil in close proximity of research labs with vibration sensitive equipment. We predict the track-soil mobility using state-of-the-art two-and-a-half-dimensional (2.5D) and periodic finite element models with perfectly matched layers, taking dynamic track-soil interaction into account. A comparison of the four track structures shows that the track-soil mobility is highest for the slab track in most of the frequency range between 1 and 80Hz. For the floating slab track, the vibration transfer is reduced by 10 to 15dB between 50 and 80Hz due to the insertion of a flexible material below the slab. Around the slab resonance frequency (20Hz), the free field response is 1 to 3dB higher compared to the slab track. For the slab track on a piled foundation, the track-soil mobility is approximately 10dB lower at frequencies below 10Hz compared to the slab track due to the higher static stiffness of the track, and close to 8dB lower at higher frequencies. The reduction at low frequencies is mainly due to the piles beneath the track, while their contribution to vibration reduction at high frequencies is rather limited. By combining a floating slab track with a piled foundation, an additional reduction of approximately 12dB compared to the slab track on a piled foundation is achieved. Hence, the total vibration reduction compared to the slab track is close to 20dB. However, the free field mobility at low frequencies increases for the floating slab track on a piled foundation compared to the slab track on a piled foundation.