Sub-ballast performance in Brazilian railway infrastructures

This paper presents a comparative analysis between two sub-ballast specifications, one used in the 1975-1985 period and another used nowadays for new railway constructions in Brazil. The main sub-ballast functions were identified, including the bearing capacity and the hydraulic conductivity. To assess the sub-ballast in terms of these technical criteria, samples were collected from two railways built more than 30 years ago, one on sandy soil and the other on stony fine aggregates. Samples of the typical fine silty soil of UNICAMP campus were also collected to evaluate the possibility of using the two types of sub-ballast on this type of soil. The samples collected in the field were tested in laboratory for evaluation of particle size, load capacity and hydraulic conductivity. Finally, the performance of each of the two granular mixtures used as sub-ballast layer in Brazilian railway infrastructures was analysed.