Identification of substructure properties of railway tracks by dynamic stiffness measurements and simulations

A new vehicle has been developed to measure dynamic vertical track stiffness while in motion. This technique allows the resonance behaviour of the track below 50 Hz to be measured. Soft soils like clay and peat are the main causes of resonance below 20 Hz. By means of simulation studies with the software VibTrain, soft soil resonance behaviour may be characterized using a few key parameters originating from track stiffness measurements, such as the minimum phase delay and corresponding frequency of the receptance transfer function. Statistical models are built to relate these key parameters with substructure properties, such as embankment thickness, shear wave velocity and thickness of the soft soil layer using pattern recognition methods. Two case studies are used to show the methodology, and the results are verified using Ground Penetration Radar (GPR) measurements and borehole investigations. Models are also developed from the statistical relationship between GPR-data and stiffness measurements. It is shown that embankment thickness is the easiest quantity to estimate, but indicative results are also presented for the other quantities (shear wave velocity and thickness of soil layer).