Advantages and limitation of using 2-D FE modelling for assessment of effect of mitigation measures for railway vibrations

K.M Norén-Cosgriff,T.I Bjørnarå,B.M Dahl,A.M Kaynia

doi:10.1016/j.apacoust.2019.06.013

Abstract

This paper addresses mitigation measures against railway vibrations in soft soils by use of FE calculations. In order for calculation models to be used as design tools, it is essential that they are relatively easy to set up and have reasonably short computational times which would allow sensitivity and optimization analyses. It is therefore desirable to use two-dimensional (2D) models to the greatest possible extent. The focus of this paper is to investigate the advantages and limitation of using such models as engineering approach to study effect of countermeasures. The difference between 2D and three-dimensional (3D) calculation models, and the performance of absorbing boundary conditions are investigated. The study shows that 2D models provide satisfactory results as long as root mean square values are considered, the treated area is long compared to other relevant distances, and the results are primarily used to compare different mitigation measures. However, since geometrical attenuation is not correctly captured in 2D models, they should not be used to calculate absolute vibration values. In a presented case study, the effects of lime-cement columns under the track bed and as a vibration-reducing screen parallel to the track are calculated and compared. The study shows good effect of both mitigation measures in the low frequency range. To avoid structure-borne noise problems, it may be necessary to combine columns below track bed with mitigation measures effective at higher frequencies, such as rail pads or ballast mats.

Highlights

Soft ground conditions often lead to complaints about excessive and annoying low-frequency vibration in dwellings along railway lines
The scaled root mean square (RMS) values indicate a good performance of the screen with about a 45– 55% reduction of the scaled RMS vibration value for distances between 20 m and 30 m from track
It is shown that as long as the basis of evaluation is RMS 1 s value, the train load can be approximated with a line load in a 2D model

Summary

Introduction

Soft ground conditions often lead to complaints about excessive and annoying low-frequency vibration in dwellings along railway lines. The authors showed that barriers are effective when the wavelength is smaller than the barrier depth, and the shear wave velocity is at least 5 times that of the surrounding soil. Several research projects performed field tests on the performance of a stiff wave barrier installed parallel to a railway line [5,6]. They used a 2.5 D coupled FE/BE model to study the efficiency of this barrier as well as subgrade stiffening next to the track in reducing railway induced vibrations. The parametric studies revealed that effectiveness of the sheet pile wall is dependent on the wall’s depth and its stiffness contrast with soil

Objectives

Results

Conclusion