Application of Elastomeric Polyurethane in Performance Improvement of Rail Ballast Subjected to Cyclic Loading

The deformation and degradation behavior of unstabilized ballast and that stabilized with elastomer and geogrid was evaluated using process simulation test (PST) apparatus at various loading frequencies ($f$). The results indicated that elastomer has significantly reduced the extent of both vertical and lateral deformations of ballast. For example, elastomer reduced the extent of vertical settlement ($S_v$) in ballast from 22.76 to 9.83 mm, and the lateral deformation ($l_d$) from 8.14 to 1.95 mm ($f=15\mathrm{Hz}$). It was also seen that the deformation and degradation of both stabilized and unstabilized ballast increased nonlinearly with the increase in the applied loading frequency ($f$). Further, the beneficial effect of elastomer in restraining the lateral flow of ballast was seen over the entire depth of treated ballast, unlike the geogrid, whose efficiency was maximum at its placement location and then reduced at farther locations. Moreover, elastomer has significantly enhanced the resilient modulus ($M_r$) and damping ratio ($D$) of ballast when compared with geogrid-reinforced ballast. For example, the elastomer increased the $M_r$ and $D$ of ballast by 25.9% and 66.6%, respectively, in comparison with an increment of only 15.1% and 25.3% in the case of geogrids ($f:15\mathrm{Hz}$). The $M_r$ and $D$ of ballast were found to be influenced by the effectiveness of the ballast stabilization technique in reducing lateral displacements. Additionally, elastomer has significantly reduced the vertical stress (${\sigma }_v$) at the ballast–subballast interface by 34%. Further, elastomer was found to be more efficient than the geogrid in reducing the dynamic amplification factor (DAF) at any loading frequency. Similarly, elastomer reduced the breakage of ballast by 71% compared with the 40% of geogrid reinforcement ($f=15\mathrm{Hz}$).