Behaviour of Clay-Fouled Geogrid-Reinforced Rubber-Coated Ballast Under Direct Shear Conditions

Rubber-coated ballast (RCB) is an inventive form of ballast produced by coating conventional ballast with recycled rubber crumb, employing an Elastan binder. The purpose of RCB is to minimize ballast breakage and thus enhances the longevity, and efficiency of railway tracks. In this study, granite, Elastan binder, crumb rubber of 0.4 mm size, and triangular geogrid were employed. The suitability of RCB was evaluated and compared with conventional ballast through the performance of the physical and mechanical tests following Indian standards (IS:2386–1963). The outcomes from the mechanical tests indicate that RCB exhibits superior resistance compared to conventional ballast. Following that, the shear characteristics and ballast breakage of unreinforced and geogrid-reinforced RCB-conventional ballast mix were investigated under various normal stresses, fouling conditions, and constant shearing rates. The outcomes of direct shear test show that the peak shear stress (τ) of both unreinforced and geogrid-reinforced RCB-conventional ballast mix reduces as the void contaminant index (VCI) content increases. Further, it is evident that with the inclusion of geogrid, the reduction rate of τ is reasonably lower as compared to unreinforced ballast. Furthermore, it is observed that in case of geogrid-reinforced RCB_50% (50% RCB mixed with conventional ballast) the τ is relatively higher or equal to unreinforced conventional ballast. Additionally, it is seen that with the increase in fouling content, the ballast breakage decreased owing to increasing cushioning. Furthermore, the insertion of geogrid considerably reduces ballast breakage compared to the unreinforced ballast.