Effect of treatment zone on the performance of polyurethane-stabilized ballast under cyclic loading

Abstract

In current study the effect of treatment zone on the performance of polyurethane stabilized ballast layer was examined under cyclic loading conditions. Test results reveal that the deformation and degradation response of ballast is significantly dependent on the depth of ballast treated with polyurethane. For a given treatment depth, the ballast samples treated only beneath the sleeper and those with treatment all along the track length has undergone similar extent of deformations and degradation. On the other hand, with the increase in treatment depth from top 75 mm of ballast (i.e. one-fifth of ballast depth) to 380 mm (full depth of ballast layer), the lateral spread reduction index (LSRI) was found to increase significantly. Further, it is evident that the polyurethane has significantly reduced the vertical stresses and improved resilient and damping characteristics of ballast. It is seen that the track stiffness (k) of all PSB samples was significantly higher than that of unstabilized ballast (USB) sample. The track life enhancement factor (Lef) defined the ratio of number of load cycles (N) required to attain the designated strains in case of stabilized ballast and unstabilized ballast is found to vary from 2000 to 60 for 0.4 % volumetric strain. The performance ranking of different PSB samples is given based on the track stiffness per unit of polyurethane used. The current study recommends the treatment of top half of ballast layer but only beneath the sleeper as it was found to be effective in improving the performance of ballast.