Experimental investigation and modelling of the mechanical behaviors of fine/coarse soil mixture

An interlayer was formed in the conventional railway track, due to the interpenetration between ballast grains and subgrade fines under the effect of train circulation. Considering the interlayer’s high bearing capacity, it has been remained in the railway track in its renewal program. In present study, the mechanical behaviors of such fine/coarse soil mixture were experimentally explored and theoretically modeled. Results show that: (i) the soil–water retention curve (SWRC) of mixture was solely related to the dry density of fine soil ρ_d-f, while independent of the coarse grain content f_v; (ii) two various fabrics of mixture were distinguished by a characteristic f_v-cha value: a fine matrix macrostructure when f_v < f_v-cha and a coarse grain dominated fabric when f_v > f_v-cha; (iii) an increasing water content induced the growth of permanent strain ${\epsilon }_1^p$ and a decline of resilient modulus M_r due to the decline of suction $\psi$, but the growth of damping ratio D_r due to the rise of soil viscosity; (iv) a constitutive model was developed for the ${\epsilon }_1^p$ by incorporating the SWRC, which allows the influences of the number of loading cycles N, deviator stress σ_d and f_v to be considered. A constitutive model was also proposed for the M_r, taking the influences of σ_d,$\psi$ and f_v into account.