The aim of the work, described in this paper, is to propose a method enabling the in-situ mechanical characterisation of railway materials from the use of acceleration records of a downhole seismic instrumentation network installed in a research facility of the national French Railway Company. This is done using some geophysical methods (i.e. interferometry and time-frequency analysis) to analyse the vibrations induced by the dynamic loading of a passing trains. According to the recorded data from the instrumented site, it is shown that the response of rail-embankment-ground system is mainly non-linear elastic.