Cyclic loading behaviour of reinforced soil–aggregate bases

The behaviour of unreinforced and geosynthetic-reinforced soil aggregate systems under cyclic loading is studied in this paper to understand the beneficial effect of geosynthetic reinforcement in unpaved road subgrades through laboratory experiments. Soil–aggregate systems were prepared in a 300 mm diameter mould by compacting clay of low plasticity to its maximum unit weight at optimum moisture content in equal lifts and placing a 50 mm high aggregate layer above the clay layer. In the reinforced soil–aggregate systems, a geosynthetic layer was introduced at the interface of the soil and aggregate. Three different types of reinforcement, namely a geotextile, a geogrid and a geonet, were used in the experiments. The soil–aggregate systems were subjected to specific sinusoidal cyclic loading in a displacement control mode up to 100 cycles. The results were analysed to understand the elastic and plastic strains developed in the systems and to compare the performance of the unreinforced and the various types of geosynthetic-reinforced systems. The resilient, cyclic and secant modulii of different systems were compared. Traffic benefit ratios of the unreinforced and reinforced systems were compared. It was observed that the reinforcement was beneficial in improving the load-carrying capacity and traffic benefit ratio of the soil–aggregate systems. Stiffer geogrids provided a better stress attenuation effect and thereby reduced the plastic deformations compared with the geotextile and low tensile strength grid. No significant improvement in the resilient modulus was observed by introducing reinforcement.