Geotechnical auscultation of a French conventional railway track-bed for maintenance purposes

Prior to renewal or maintenance works on a railway track it is required to perform a proper investigation of the stiffness and thickness of each material constituting the track-bed. In practice, different techniques are used for this purpose. In this study, a comparison of two methods of determining the stiffness of track-bed materials (dynamic penetration and dynamic plate load) is made for a representative French conventional railway line, aiming at optimising the use of different geotechnical auscultation techniques for the railway applications. Firstly, results from geo-endoscopic tests are analysed to define the thickness and nature of the different materials found in the track. Then, dynamic penetration tests (PANDA tests) are performed to evaluate the stiffness of the different layers. Statistical distribution of soil stiffness is analysed for each layer. In addition, the elastic moduli of different materials are estimated from their stiffness using empirical equations. Secondly, dynamic plate load tests using a light weight deflectometer device (LWD) are carried out on surfaces (on tracks and service paths) in order to estimate the dynamic and static moduli of ballast and subgrade. A statistical analysis of the obtained results shows a low dispersion rate and a satisfactory repeatability. The static moduli estimated from LWD tests are found to be consistent with the elastic modulus estimated from PANDA tests, showing that different auscultation methods give complementary information about the mechanical properties of the materials constituting the conventional tracks.