The Influence of Particle Size Distribution on Mechanical Performance of Tropical Soils as Sub-Ballast Material

According to the MCT, a Brazilian specification for fine grained tropical soils classification, a soil sample must have 90% of the particles passing through sieve nº10 in order to be tested. Soils with coarser granulometry should be sorted using traditional classification systems, such as the Transportation Research Board (TRB) and the Unified Soil Classification System (USCS). Yet, many coarser tropical soils cannot be properly evaluated by traditional classification systems due its fine particles, making its applications as sub-ballast layer unfeasible. Therefore, some researches demonstrate that its mechanical behavior of coarse tropical soils are appropriated for sub-ballast use. In this perspective, repeated load triaxial tests were conducted to assess its mechanical performance in terms of resilience module and permanent deformation. These parameters were used to evaluate the application of the mentioned soils as a sub-ballast layer. The results of the particle size distribution and the soil classification tests shows that the analyzed samples are not recommended for sub-ballast layer use according to TRB/USCS and could not be tested by the MCT. The repeated load triaxial test indicated the occurrence of the Shakedown for 6 out of 8 samples. Based on the resilience module results, the allowable stress was calculated, resulting in a range of values from 100 to 245 kPa. It was concluded that the studied soil could be used as sub-ballast layer, despite not being properly classified according to TRB, USCS, and MCT classification methodologies.