Engineering Performance and Interface Shear Behaviour of Crumb Rubber-Stabilized Clay Subgrade Reinforced with Geogrid

Clayey soils are generally characterized with low strength and high plasticity which may affect the stability of the subgrade in road infrastructure and hence encourage research into sustainable stabilization techniques. The objective of this study was to investigate the possibility of using recycled crumb rubber (CR) mixed with biaxial geogrid reinforcement to enhance the engineering performance and interface shear behaviour of problematic clayey soil. The experiments were performed on biaxial geogrid BX1100, waste crumb rubber, clay subgrade soil, type B subbase granular material and other materials. The subgrade soil of clay has been collected from the airport area of Al-Muthanna region, Baghdad. An extensive programme of laboratory tests was conducted on soil mixtures with 5%, 10% and 15% of crumb rubber (CR) and untreated soil to determine the effect of stabilization with crumb rubber. The protocol consisted of Atterberg limits, modified Proctor compaction, California Bearing Ratio (CBR) and large-scale direct shear testing. The results showed that the engineering properties of the clay soil were improved by using CR. Maximum improvement was observed at 15% CR content where CBR increased by 56.6% and plasticity index decreased by 44% over the untreated soil. In addition, the large-scale direct shear tests showed that the interface shear strength increased with increasing CR content under geogrid reinforcement. The calculated interaction coefficients were greater than unity for all the tested mixtures indicating effective bonding and interlocking between the reinforced soil layers. The results indicate that the synergistic effect of CR and geogrid reinforcement could improve the interface behaviour of the weak clay subgrade soils with sustainable reuse of waste tyre rubber.