Swelling granular media can experience size-induced percolation phenomena giving rise to segregation. In this work, the Discrete Element Method is employed to investigate the effects of size ratio and swelling kinetics on the segregation. The numerical analysis was carried out on a binary mixture consisting of coarse and fine particles and several mixing indices found in literature were adapted and tested for evaluating the mixing of expanding systems. Additionally, a relative percolation velocity was employed to quantify the percolation of fine particles. The results show that the percolation of fine particles becomes more significant as the size ratio increases. Additionally, results showed that the swelling kinetics has no impact on the segregation tendency. This research provides valuable insight into the effect of size ratio and swelling kinetics on the segregation behaviour of swelling granular materials, which can contribute to understanding percolation phenomena in various fields.