An interlayer soil in ancient rail tracks was identified as a mixture of ballast grains and subgrade fines. As the permanent strain 휀 1 푝 of such mixture was affected by water content, cyclic triaxial tests were performed, under varying water contents of fines wf and coarse grain contents fv. Comparison between present and previous studies showed the significant effect of sample preparation method on 휀 1 푝. In present study, a constant fine dry density ρd-f was maintained, leading to an unchanged suction of mixture whatever the fv value. In this case, only the reinforcement effect of fv on 휀 1 푝 was identified. By contrast, in previous studies, the global dry density of mixture ρd was kept constant, resulting in a decrease of ρd-f with increasing fv and consequently a decrease of suction. In this case, when the negative effect of decreasing suction prevailed on the positive reinforcement effect of increasing fv, the 휀 1 푝 increased.