Calibration of a high-cycle accumulation model for granular materials of railway track layers using tests of variable cyclic load amplitudes

Abstract

The top granular layers of railway tracks, including ballast and sub-ballast, are essentially resilient structures, where the deformation imposed by one passing train is mostly recovered elastically, with only a very small part being permanent non-recoverable deformation. These residual deformations however accumulate over the hundreds of thousands of axle’s passages that take place every few months of service operation. This leads to differential settlements and deteriorated track geometry, which ultimately requires intervention and correction. In places where differential settlements develop fast, this leads to high maintenance costs and sometimes speed restrictions during service operation. Furthermore, this long-term deterioration process of railway tracks alters the short-term dynamic interaction between vehicle and track. The dynamic vehicle-track loading will alter significantly soil stress levels in contiguous segments of the track, therefore playing a role in the accumulation of permanent deformation along the track, thus further contributing to additional differential settlements. These two coupled phenomena must therefore be treated simultaneously. This is a non-linear three-dimensional problem in nature. Reduction to 2D or 1D imposes significant limitations. These types of models describe the generalized behaviour but are not able to describe the phenomena in the soil at a material level. Computational numerical approaches that simulate complex phenomena are nowadays common practice. The dynamic simulation of railway vehicle-track interaction with complex 3D geometries and constitutive laws is nowadays feasible. However, the integration of these numerical tools with models that simulate the permanent deformation of granular materials is still scarce. This work concentrates on the calibration of a high cyclic accumulation material model based on laboratorial triaxial testing. This type of model is essential for the usage of 3D finite element models for permanent deformation of a railway track.