Pieter Coulier

Stiff Wave Barriers for the Mitigation of Railway Induced Vibrations

This paper studies the efficiency of stiff wave barriers for the mitigation of railway induced vibrations. Coupled finite element–boundary element models developed at KU Leuven and ISVR are employed; these models have been cross–validated within the EU FP7 project RIVAS (Railway Induced Vibration Abatement Solutions). A first mitigation measure consists of a block of stiffened soil embedded in a halfspace that acts as a wave impeding barrier. The existence of a critical frequency from which this mitigation measure starts to be effective, as well as a critical angle delimiting the area where the vibration levels are reduced, is demonstrated. Next, a sheet piling wall is considered, accounting for the orthotropic behaviour of this wall. Calculations show that the reduction of vibration levels is entirely due to the relatively high axial and bending stiffness in the vertical direction (along the profiles), while the bending stiffness for bending waves traveling in the longitudinal direction (perpendicular to the profiles) is too low to affect the transmission of vibrations. Field tests are being carried out in Spain and Sweden to confirm the conclusions of these numerical computations.

Dataset for the figures in 'Reducing railway-induced ground-borne vibration by using open trenches and soft-filled barriers'

Data for the figures in the paper by Thompson, D., Jiang, J., Toward, M.G.R, Hussein, M.F.M., Ntotsios, E., Dickmans, A., Coulier, P., Lombaert, G. and Degrande, G. (2016) Reducing railway-induced ground-borne vibration by using open trenches and soft-filled barriers. Soil Dynamics and Earthquake Engineering

Experimental and numerical evaluation of the efficiency of a stiff wave barrier in the soil

This paper discusses the design, the installation, and the experimental and numerical evaluation of the effectiveness of a stiff wave barrier in the soil as a mitigation measure for railway induced vibrations. A full scale in situ experiment has been conducted at a site in El Realengo (Spain), where a barrier consisting of overlapping jet grout columns has been installed along a railway track. This barrier is stiff compared to the soil and has a depth of 7.5m, a width of1m, and a length of 55m. Geophysical tests have been performed prior to the installation of the barrier for the determination of the dynamic soil characteristics. Extensive measurements have been carried out before and after installation of the barrier; this paper focuses on free field vibrations during train passages. Measurements have also been performed at a reference section adjacent to the test section in order to verify the effect of changing train, track, and soil conditions over time. The in situ measurements show that the barrier is very effective: during train passages, a reduction of vibration levels by 5 dB is already obtained from8Hz upwards, while a peak reduction of about 12 dB is observed near 30Hz immediately behind the barrier. The performance decreases further away from the jet grouting wall, but remains significant. This in situ test hence serves as a ‘proof of concept’, demonstrating that stiff wave barriers are capable of significantly reducing vibration levels, provided that they are properly designed.

A NUMERICAL STUDY OF SUBGRADE STIFFENING AS A MITIGATION MEASURE FOR RAILWAY INDUCED VIBRATIONS THROUGH 2.5D AND 3D FE-BE MODELS

This paper studies the efficiency of subgrade stiffening next to the track as a mitigation measure for railway induced vibrations by means of a two-and-a-halfdimensional coupled finite element – boundary element methodology. The pyhsical mechanism is interpreted in the frequency–wavenumber domain, illustrating that the stiffened block of soil next to the track can act as a wave impeding barrier. The existence of a critical frequency from which this mitigation measure starts to be effective, as well as a critical angle delimiting the area where the vibration levels are reduced, is demonstrated in this paper. Two realistic ca se studies are discussed to indicate that the effectiveness of the proposed mitigation measure depends on the stiffness contrast between the soil and the stiffened block of soil. Keywords— Dynamic soil-structure interaction, railway induced vibrations, mitigation measures on the transmissi on path, frequency–wavenumber analysis

Coupling of finite elements and hierarchical boundary elements for dynamic soil-structure interaction problems

Abstract. This paper discusses the coupling of finite element and fast boundary element methods based on hierarchical matrices to solve problems of visco–elastodynamic wave propagation involving dynamic soil–structure interaction in the frequency domain. Three coupling methodologies are presented and their computational performance is assessed through numerical examples. It is demonstrated that a direct coupling approach, in which the boundary element domain is condensed into an equivalent dynamic stiffness matrix, is the least efficient. Iterative procedures provide a valuable alternative; the efficiency of these algorithms strongly depends on the kind of boundary conditions applied to each subdomain, however. The fastest convergence is observed if Neumann boundary conditions are imposed on the most stiff subdomain. Aitken’s ∆–method is employed in these schemes for the calculation of an optimized interface relaxation parameter in order to ensure and speed up the convergence. A monolithic coupling approach is presented as well, providing a simultaneous solution of the governing equations while avoiding the assembly of a dynamic soil stiffness matrix.