Page 267 - 360.revista de Alta Velocidad - Nº 5

Calculation and rational dimensioning of railway infrastructure materials using numerical modelling

First, the description the methodology adopted in the realization of said numerical model,
followed by a description of the characteristics and cases of analysis considered in the mime;
then the main results obtained from the resolution of the calculation by the numerical
model will be presented, being these mainly values of seats and vertical tensions in the
different layers.

2. Methodology

The study of the geotechnical behaviour of the railway platform is one of the most difficult
problems in the field of civil engineering in terms of its resolution and interpretation of
the results obtained. From the outset, this problem has been approached through the
use of classical analytical solutions obtained from the use of Elasticity Theory hypotheses
(Winkler, 1867; Poulos and Davis, 1974; Jimenez Salas, 1981) until the and the development
of new mathematical and numerical tools (Indraratna, 2016), such as the Finite Element
Method (MEF) and Discrete Elements Method (MED) (McWilliams, et.al., 2000; Huang and
Tutumluer, 2011) has made it possible to solve this problem in a more precise way, allowing
the addition of new variables that try to reproduce more accurately the behaviour of the
railway platform.
One of the effects that computers and numerical methods had on the calculation of railway
platforms was the possibility of modelling the behaviour of the materials of the platform in
its elastic or plastic form together, thus integrating the model of elastoplastic behaviour;
On the other hand, it was also improved the capacity of calculation before cases of loads
that considered the variation in the space and time of this one, giving place to the dynamic
analyses of load in railway platforms with a wide development in our days. However, these
two aspects are not yet fully integrated into current numerical models, since the use of
the Plasticity Theory hypotheses requires the study of complex constitutive laws and the
use of additional mechanical parameters that are not required if It is assumed an elastic
behaviour of the materials and therefore, many current numerical models still assume
elastic or derivative behaviour models as the hyperbolic model (Gallego, et al., 2013; Shih,
et.al., 2017). With respect to dynamic analysis, most of the commercial software that
operate with the use of finite elements have tools that allow the modelling of mobile load
cases and dynamic properties of materials, thus having a greater difficulty in adequately
characterizing the geomechanical behaviour of these.
The numerical model presented here allows to model the geometry and the elements
that form the section of railway platform used in the Spanish High-Speed. Different
recommendations and modelling methodologies used by different have been used for its
elaboration, being the most outstanding recommendations in normative series (Ministerio
de Fomento, 1999) and, as numerical models, those made by Gallego (2012) and others
(Gallego, et.al., 2013).

With the orientation of these existing models, it has been refined or improved in the same
as will be seen, by eliminating the ballast material that confines, in the transverse and
longitudinal direction, the sleepers of the platform, generating a model with confining
ballast and without it. In addition to this, a deepening in the interpretation of the results
that obtain numerical resolution is made, comparing these assuming both a constitutive
model of elastic behaviour and elastoplastic for the granular materials that form the seat
layers of the platform, all for a simple static load case.

Finally, for the calculation of the numerical model and the interpretation of the results
obtained, a sensitivity analysis was carried out by varying the value in one of the resistant
parameters of the granular materials that form the railway platform, these being in
particular the Formation layer and Subballast.

International Congress on High-speed Rail: Technologies and Long Term Impacts - Ciudad Real (Spain) - 25th anniversary Madrid-Sevilla corridor 265