Sub-ballast performance in Brazilian railway infrastructures

Abstract

In the period 1975–1985 several new railway infrastructures were built in Brazil. After this period the construction of new railways stopped. With the new railway concessions in 1996, minor maintenance work was undertaken on the old railway infrastructures and only in the last six years have new railway infrastructures begun to be constructed. In São Paulo, between 1978 and 1985, some old railways infrastructures were also rebuilt using sub-ballast or platform with granular soils in the track layers.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.