Performance Prediction and Validation of Railway Ballasted Trackbed and Crumb Rubber Modified Asphalt-Ballast Trackbed in the Tropics

Abstract

The granular sub-ballast in ballasted trackbed, though cheap and easy to construct, requires frequent maintenance, and cannot protect the subgrade against water infiltration. However, asphaltic sub-ballast in asphalt-ballast trackbed can reduce stresses on the subgrade and provides a waterproofing layer against water infiltration. The aim of this research, therefore, is to replace the granular sub-ballast with asphaltic sub-ballast, and compare the performance of the two track types. The study used the finite element package, KENTRACK software to calculate the tensile strains and compressive stresses, in five different layer thicknesses of granular sub-ballast and asphaltic sub-ballast. The calculated tensile strains and compressive stresses were used to predict the service lives of the two track types, using multiple regression analysis. The numerical simulation results showed that the asphalt-ballast trackbed has a much longer predicted service life than the ballasted trackbed. The inclusion of asphaltic sub-ballast in the trackbed reduced deformations and stresses on the subgrade. One significant finding was that the service life of asphalt-ballast trackbed due to 100 mm thick asphaltic sub-ballast was 33.28 years, while the service life of ballasted trackbed due to 200 mm thick granular sub-ballast was 28.56 years, under the same loading conditions. KENTRACK software results were validated by using measuring devices. Results showed no significant difference between the KENTRACK predicted and the validation values. The study concludes that asphaltic sub-ballast, offers higher ability to transmit stresses down to the subgrade, resulting in increased service life. It reduces maintenance costs and ensures passenger’s comfort and safety.