One increasingly important problem associated with conventional railway tracks is the deterioration of the track and increase of differential settlements due to the construction of new underpasses. Critical zones created around the those structures when pushing them against railway embankments impose serious limitation to the operational speed of the lines causing maintenance cost increments. In this paper, the works carried out to improve the transition zones in an old 8 m high embankment, where a concrete underpass was jacked several years ago, are described. In order to determine the variability of the materials involved and to define the behaviour of the embankment and its foundation, a borehole was drilled in the track and a sliding micrometer was installed inside. Besides, the current behaviour of the track under the daily traffic of trains was investigated before and after retrofitting the line.