  We study the segregation of granular mixtures in two-dimensional silos using
a set of coupled equations for surface flows of grains. We study the thick flow
regime, where the grains are segregated in the rolling phase. We incorporate
this dynamical segregation process, called kinematic sieving, free-surface
segregation or percolation, into the theoretical formalism and calculate the
profiles of the rolling species and the concentration of grains in the bulk in
the steady state. Our solution shows the segregation of the mixture with the
large grains being found at the bottom of the pile in qualitative agreement
with experiments.
