Effect of Polyurethane Treatment Depth on the Performance of Geogrid-Polyurethane Composite-Stabilized Ballast

Abstract

The effect of polyurethane treatment depth on the behavior of geogrid-polyurethane composite-stabilized ballast (CSB) was evaluated based on large-scale cyclic tests. The geogrid was placed at the ballast–subballast interface, and polyurethane treatment depth of 76 and 152 mm from the sleeper soffit was considered for tests. The test results show that the vertical settlement of CSB decreased from 20.2 to 16.1 mm as the polyurethane treatment depth increased from 76 to 152 mm. Further, the stabilization efficiency factor (S_ef, _cyc ), track stiffness (k), and resilient modulus (M_r) of the CSB increased from 0.36 to 0.56, 55.9 to 66.1 MN/m, and 269.7 to 275.7 MPa, respectively, with the increase in treatment depth from 76 to 152 mm. The results from the current study were critically compared with those available in literature for treatment depths of 228 mm and fully treated polyurethane-stabilized ballast. It was seen that the improvement in S_ef, _cyc and k per unit of polyurethane was highest for treatment depth of 76 mm. Further, the track life enhancement factor (L_ef), the ratio of the number of load cycles to reach 2% vertical strain by stabilized and unstabilized ballast, was determined to be 15.7. Although the lowest, the obtained L_ef would imply an ~16 times increment in load cycles to cause 2% vertical strain. Thus, CSB with geogrid at the ballast–subballast interface and polyurethane treatment depth of 76 mm below the sleeper soffit was found to be an economically viable and practically feasible approach to stabilize the ballasted track.