Vibratory impact of infrastructures

 

What is it?

The existing transport infrastructures in a specific region are sources of noise and vibration, generating an annoyance on the people living near them. Great advances has been achieved in the past three decades on noise control of transport infrastructures. Nowadays it is a well-established and normalized engineering subject. In contrast, vibration control has traditionally remained in the background. However, its importance is growing increasingly once the noise problem has been solved by means of underground infraestructures, the inclusion of acoustic screens, acoustic pavement, etc... Specifically, in recent years, the vibratory impact of railways has taken on special importance due to the emergence of high speed lines.

 

Field experience

The LEAM has been working for over 10 years on the phenomenology associated with the vibration impact of railway infrastructure. In this context, the group has done large amount of impact assessment studies for different companies and administrations, and has formed or currently forms part of research projects focused on the prediction of this vibration impact, such as the CATdBTren project and the RECYTRACK project, among others.

 

Vibration impact assessment

For the assessment of vibration impact, LEAM has proper instrumentation to do such studies, carrying out experimental measurement campaigns (mainly with LMS Pimento as multichannel equipment and seismic and piezoelectric accelerometers) as well as in-house computer programs specifically designed to perform the post-processing of the signals acquired according to current regulations and standards.

 

Figure 1. Vibration impact assessment.

 

Vibration impact prediction

About the vibration impact of railway infrastructures, LEAM has focused its research on the developing of a model able to obtain vibration isophones caused by a railway infrastructures with very small computational and, above all, engineering costs [1]. This model is now operative and, for example, it has been recently used in the frame of the RECYTRACK project to characterize the vibration abatement efficiency of elastomeric under ballast mats and isolated blocks designed by ACCIONA Infraestructuras. The huge computational savings achieved by this model have been achieved by new analytical/numerical improvements in the calculation of the ground response, finding new ideas and techniques [2,3,4]. About the engineering costs, the model can predict the vibration impact induced by a new infraestructure with only the significant mechanical properties of all major systems that make up the complete problem: vehicles, superstructure, ground and buildings. It can also be used to determine the vibration levels in future buildings that are planning to be built near an existing railway infrastructure.

 

Figure 2. Vibration impact of major railway lines.

 

LEAM is also working on a model able to perform similar predictions in the case of underground infrastructure [5]. The specific case of a tunnel with an inner floor partition has been recently studied in detail [6,7], which is the solution in some streches of new metro line (L9) of Barcelona's metro network.

 

Figure 3. Tunnel with inner floor partition in L9 of Barcelona's metro network.

 

Additionally, LEAM is developing an in-situ dynamic characterization system for railway superstructures, which will allow us to determine the dynamic properties of the ground-superstructure system.

 

LEAM has also the capacity to perform detailed studies of the vibration impact using the finite and boundary element methods (FEM and BEM, respectively) with a 2.5D FEM/BEM code completely developed in the lab. LEAM has used this technology in several projects about vibratory impact assessment of specific new railway lines, and for characterize specific isolation measures, such as vibration isolation screens, under-ballast elastomeric mats, isolated blocks, under-rail elastomeric pads, etc...

 

Figure 4. Mesh geometry of a 2.5D FEM/BEM model used to predict the vibration isolation efficiency of a composite vibration isolating screen used to isolate a building structure from an underground railway line.

 

The group has also the capacity to carry out full 3D studies using a 3D FEM/BEM an in-house solver, which has a higher computational efficiency in the case of this specific problem than typical commercial 3D FEM solvers, such NASTRAN, ANSYS or ABAQUS.

 

References

 

[1] R. Arcos. A model for railway induced ground vibrations in the frame of preliminary assessment studies. PhD thesis, Universitat Politècnica de Catalunya, 2011.

[2] R. Arcos, J. Romeu, A. Balastegui, and T. Pàmies. Determination of the near field distance for point and line sources acting on the surface of an homogeneous and viscoelastic half-space. Soil Dynamics and Earthquake Engineering, 31(7):1072–1074, 2011.

[3] R. Arcos, J. Romeu, A. Clot, and M. Genesca. Some analytical aspects of viscoelastic Lamb's problem for improving its numerical evaluation. Wave Motion, 50(2):226–232, 2013.

[4] R. Arcos, A. Clot, J. Romeu and S.R. Martín. Fast computation of an infinite, longitudinally-varying and harmonic strip load acting on a viscoelastic half-space. European Journal of Mechanics - A/Solids, 43:58-67, 2014.

[5] A. Balastegui, R. Arcos, J.I. Palacios and J. Cardona. Surface vibration pattern induced by underground trains. In Proceedings of 37th International Congress and Exposition on Noise Control Engineering, 2008. Internoise 2008 Conference, Shangai, China.

[6] A. Clot, J. Romeu, R. Arcos and S.R. Martín. A power flow analysis of double-deck circular tunnel embedded in a full-space. Soid Dynamics and Earthquake Engineering, 57:1-9, 2014.

[7] A. Clot. A dynamical model of a double-deck circular tunnel embedded in a full-space. PhD thesis, Universitat Politècnica de Catalunya, 2014.