Sustainable Valorization of Waste Carpet into Geogrid Reinforcement for Bearing Capacity Enhancement of Sand

In recent years, geosynthetic reinforcements such as geogrids have been verified as efficient at improving the performance of weak soils. At the same time, disposing of waste materials, such as waste carpets, poses a significant environmental challenge. For example, most carpets are made of durable synthetic materials like nylon, polypropylene, or polyester, which degrade slowly in landfills. Recycling these materials into useful products can reduce environmental impact and promote sustainable construction practices. To investigate the pressure-displacement behavior of a square plate placed on both reinforced and unreinforced soil, a series of plate-loading model investigations were implemented. The objective of the test series was to examine how bearing capacity and displacement are affected by the relative densities (R.D.), the initial reinforcement layer's depth (u/B), the reinforcement layer numbers (N), and the interlayer distance between the waste carpet grid (WC-grid) layers (h/B). These studies were carried out for relative densities of 30%, 50%, and 70%, with a variety of u/B ratios, including 0.2, 0.3, 0.4, and 0.5, and h/B ratios of 0.2, 0.3, 0.4, and 0.5. As anticipated, the bearing capacity of both unreinforced and reinforced soil increases as their relative densities rise. A single layer (initial layer) of WC-grid reinforcement in loose sand, the percentage improvement reached 93% (with an improvement factor, IF = 1.93) and reduced the displacement by 80% compared to unreinforced sand when the relative density is 30%, and the spacing between the plate and the initial layer is (u/B = 0.2). The results demonstrated that increasing the number of WC-grid reinforcement layers enhanced the bearing capacity of the reinforced soil. For the two-layer reinforcement system (N = 2), the maximum percentage improvement reached approximately 117% (with an improvement factor, IF = 2.17) was achieved at a reinforcement width ratio of u/B = 0.2 and a first-layer depth ratio of h₁/B = 0.3, at a relative density of 30%. For the three-layer reinforcement system (N = 3), the maximum percentage improvement reached approximately 153% (with an improvement factor, IF = 2.53) under the same conditions of u/B = 0.2 and h₁/B = 0.3, with the optimum second-layer spacing corresponding to h₂/B = 0.3 and a relative density of 30%. These findings indicate that increasing the number of reinforcement layers from two to three can further enhance the bearing performance of WC-grid-reinforced soil, provided that the reinforcement layers are positioned at their optimum depths.