Experimental evaluation and design framework for geocomposite-reinforced working platforms on soft subgrades

Abstract Working platforms are critical temporary geotechnical structures used to support heavy construction equipment operating over weak cohesive subgrades. Their performance depends on the ability of the platform system to distribute applied stresses, mobilise sufficient bearing resistance, and maintain operational stability. Conventional design methods are largely based on unreinforced two-layer foundation theory and empirical guidance, with limited provisions for quantifying geosynthetic reinforcement effects. Although recent industry guidance recognises the benefits of geosynthetics, experimentally validated, design-oriented methodologies remain limited. This study experimentally investigates the reinforcement effect of geocomposites, which are hybrid geosynthetics combining geogrid reinforcement and geotextile separation, installed at the subgrade–capping layer interface. Large-scale static plate load tests were conducted in an instrumented steel model box (1.0 m × 1.0 m × 1.2 m) to simulate field-representative boundary and loading conditions. Soft clay subgrades were prepared to target California Bearing Ratio (CBR) values of 2.5% and 1.0%. Monotonic loading was applied through a 200 mm diameter plate at a displacement rate of 1.0 mm/min to evaluate the influence of capping layer thickness, subgrade stiffness, and geocomposite inclusion on ultimate bearing capacity and stress distribution. Results show that geocomposite inclusion significantly increases ultimate bearing capacity, with the greatest relative improvement observed at lower capping thicknesses. Beyond a critical thickness, additional granular material provides diminishing gains. A performance-based design chart was developed to estimate required capping thickness for target bearing capacity in reinforced working platforms, supporting cost-effective and structurally efficient design over soft cohesive subgrades.