Using recycled plastic posts and geogrid to resist soil sliding

This study investigates the effectiveness of a slope reinforcement system consisting of a network of recycled plastic posts interconnected at the slope surface with a geogrid. Centrifuge and numerical modelling were performed to study the shear resistance of soils reinforced by posts with or without geogrid connection. A large-area, direct shear apparatus that can be mounted on a centrifuge was utilised so that a soil block could be sheared at a predefined slip depth under a prototype-scale effective stress state. Eleven tests were conducted to study the effects of soil density, post spacing, and geogrid connection on the shear behaviour of the reinforced soil. The soil–structure interaction was analysed by the beam-on-non-linear-Winkler-foundation approach. The reinforcement effect was maximum when slip occurred at the mid-length of the post. For a deep slip, the reinforced soil followed an “intermediate mode” of failure, where the soil strength was fully mobilised along the post length. The geogrid increased the shear resistance of the reinforced soil, but these benefits were at the cost of additional mobilisation of bending stresses within the connected posts. Despite the significant improvements of soil stability, careful monitoring of the reinforced system might be required to prevent post overstress and yielding.