Waste plastic bottle mattress for sustainable soil bearing capacity improvement

The increasing accumulation of non-biodegradable PET bottles has raised serious environmental concerns, highlighting the need for sustainable recycling strategies. This study proposed an engineered mattress system made of waste plastic bottles (WPB) for soil improvement through laboratory and field tests. A series of physical model tests was carried out on circular footing resting on loose sand, reinforced with WPB mattresses. The effects of mattress height, placement depth, and mattress width were investigated. The results show that increasing mattress height and width, while reducing placement depth, significantly improves the foundation bearing capacity and stiffness. Compared with the unreinforced condition, this mattress increased the ultimate bearing capacity by up to 500% and the initial stiffness by 2100%, depending on the mattress configuration. In addition, increasing mattress height and width enhanced pull-out resistance, thereby changing the governing failure mechanism from mattress sliding to mattress connection rupture. The field tests further confirmed the beneficial effect of the WPB mattress on subgrade response. Overall, the proposed WPB mattress offers an environmentally friendly recycling WPB while improving the geotechnical performance of loose soils. The system may be used as a shallow ground improvement technique for weak sandy subgrades, particularly beneath small and relatively light foundations.