Influence of Clay Fouling on the Performance of Geogrid–Polyurethane Composite-Stabilized Ballast

Contamination (fouling) of ballast by clayey sediments decreases the angle of friction of the granular assembly, thus compromising its load-bearing capacity and the shear strength. Although recent studies have introduced the concept of geogrid–polyurethane-based composite-stabilized ballast (CSB), which performs significantly better than any unstabilized ballast (USB), the effect of clay fouling within a CSB layer has not been evaluated. Therefore, in the present study, the effect of clay fouling on the behavior of CSB was evaluated based on large-scale cyclic tests. Five different CSB samples with varying geogrid placement positions and the top 76, 152, and 228 mm of ballast treated with polyurethane were assessed. The samples were fouled to have void contamination indexes (VCIs) ranging from 0% to 45%. The test results indicated that the deformations of CSB samples increased with clay fouling, whereas the resilient modulus ( M r ), damping ratio ( D ), and track stiffness ( k ) decreased. However, the CSB samples exhibited a reduced extent of deformations and increased values of M r , D , and k . Moreover, visual inspection of retrieved CSB samples in which the top 76 mm was treated indicated that irrespective of geogrid placement position, the polyurethane bonds began to break at VCI = 45%.