Numerical and in-situ investigation on bilateral double-wall barriers in mitigating metro train-induced vibrations

Abstract

In the case of metro tunnels crossing through the area with buildings on both sides in a densely populated mega city, it is necessary to apply a countermeasure to mitigate metro train-induced vibrations on both sides. To achieve this goal, a vibration mitigation measure concept of bilateral double-wall barriers (BDWB) is proposed, in which a wall-soil-wall composite as a double-wall barrier is set in the propagation path from the tunnels to the buildings at one side of the tunnels and, typically, is symmetrically installed at the other side. The performance of the BDWB in a homogeneous halfspace is examined using a 2.5D finite element methodology. The wall-soil-wall composite is idealized as a Timoshenko beam model and its bending dispersion curve is analytically obtained by a simplified method. The physical mechanism of the BDWB is interpreted, indicating the dominance of the bending mode of the wall-soil-wall composite and the influence of a phase shift caused by the compressive wave velocity difference in the BDWB. A series of full-scale in-situ tests are conducted to investigate the isolation performance of the BDWB, followed by a comparison with the corresponding numerical analysis. The results show that a BDWB of 24.5 m depth in the test site can effectively reduce the vibrations behind the BDWB with a maximum average insertion loss of up to 24.3 dB. Results from the in-situ test and the numerical analysis confirm the potential of the BDWB in isolating metro train-induced vibrations.