Assessment of critical train speeds of railways on soft soils - a case study
The dynamic interaction between the railway traffic, the track bed and the subsoil can lead to excessive deformation, including resonance issues, when train speeds approach the critical velocity. This leads to unacceptable track maintenance and potentially compromises safety leading to track closure. This study investigates the critical train speed along a main railway track in Switzerland, a strategic corridor for both passenger and freight transportation. The line crosses several wetlands. The geological setting consists of floodplain deposits of peat, clay, and silty alluvium overlying sand and gravel layers, with locally variable thicknesses. Extensive geotechnical site investigations were carried out, comprising 34 seismic and non-seismic cone penetration tests that provided down-hole shear wave velocity measurements. The dataset was processed using state-of-practice correlations to derive soil parameters, with special attention to organic soils. Statistical processing enabled the development of a two-dimensional stochastic subsurface schematization of the railway alignment. Stochastic analyses were performed to quantify the influence of parameter uncertainty. This enabled a stochastic assessment of the critical train speed, quantifying uncertainty and supporting the prioritisation of locations and parameters requiring further investigation.