Effect of water content on permanent deformation of fine/coarse soil mixtures with varying coarse grain contents and subjected to multi-stage cyclic loading

Abstract

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