Large-Scale Direct Shear and Discrete Element Modelling Investigations of Ballast, Sub-Ballast, and Sleeper Interface Characteristics in a Railway Track Structure

A typical railway track structure is composed of different layers of constituent materials. The resulting contact interface between these layers results in displacement discontinuities and largely influences the strength-deformation behavior of the system. In order to assess and quantify the interactions that take place at these interfaces, the present study conducts Discrete Element Analysis (DEM) of large-scale direct shear interface tests using Altair EDEM software. These simulations use the extensive laboratory investigations earlier performed by [1] for validation. The shear stress parameter of the ballast-sub-ballast, ballast-concrete sleeper, ballast-steel sleeper, and ballast-geogrid are taken into consideration for this study. The contacts generated at the interfaces of different elements are also realized here. Since the contact interface behavior is largely influenced by the shape of the ballast, the number of contacts, and the inherent discontinuities, therefore the calibration of the modelled ballast and sub-ballast particles is also done in terms of static angle of repose value and bulk density before the actual test simulation. The plots of shear stress vs horizontal displacement values are obtained by extracting and relating them using the time parameter. The EDEM simulation results for the test cases are found in agreement with the laboratory test results with the variation lying within the range of ± 10%. The variation witnessed here may be because of the assumptions that are made during the simulation in order to reduce the computational time requirement.