Case study on the rehabilitation of old railway lines: experimental field works

Résumé

In many countries, old railways have to be renewed in order to fulfil modern
quality requirements, related either to higher travel speeds or to greater axle loads. When
renewal works are required it is usual to replace the superstructure, laying new support layers
and, in some cases, improving the subgrade soils. Preferably, such renewal works should be
carried out in an economical and environmental sustainable process, taking into account the
existing materials and the in situ conditions of the structure. It is necessary to carry out
evaluation studies of the physical and mechanical properties of the existing elements as well
as of the materials to be used in the renewal process. Different structural solutions can be
established for rehabilitation purposes, regarding the existing track conditions. Among other
aspects, the design of these structural solutions depends on the hydrogeological conditions
that occur along the line, on the characteristics of the foundation soils and on the existing
ballast layer. In old lines it is often observed a layer of fouled ballast on the top of the
foundation soil. During the renewal there are some technical, economic and environmental
advantages in maintaining the fouled ballast layer under the new reinforcement layers. These
advantages are related to the high stiffness of that layer and to the reduction in supply, deposit
and transportation of materials. This paper presents some results of experimental work carried
out on a deactivated rail stretch, used as an experimental site. This study was performed in
order to assess the feasibility of some structural solutions, using reinforcement layers built
with unbound granular materials (UGM) and cement bound granular mixtures (CBGM).