Optimizing Foam Lightweight Soil Embankments: Enhancing Stability and Mitigating Settlement in Soft Soil Foundations

Foam lightweight soil (FLS) has emerged as a promising material in geotechnical engineering due to its low density, high load-bearing capacity, and ability to incorporate industrial by-products such as fly ash. It offers significant advantages in mitigating settlement and improving stability for embankments constructed on soft soil foundations. However, the combined influence of key parameters—including layered filling thickness, bulk density, and geogrid reinforcement—on the long-term performance of FLS embankments remains insufficiently understood. This study investigates the settlement behavior and stability of FLS embankments through a combination of field experiments and finite element simulations over a 15-year period. The results indicate that layered filling thicknesses of 500–600 mm achieve the best balance between settlement control and construction feasibility. When the thickness exceeds 800 mm, not only does the uniformity deteriorate, but the settlement also increases. Experimental results showed that a medium bulk density of 6 to 8 kN/m3 is optimal as a balance between strength and settlement behavior. Furthermore, geogrid reinforcement significantly improved stability, with safety factors increasing by up to 1.87 compared to unreinforced sections. The findings provide practical guidelines for the design and construction of FLS embankments, particularly for bridge approaches and soft soil foundations. In addition to improving structural performance, the incorporation of industrial by-products highlights the potential of FLS as a sustainable and cost-effective material for future infrastructure development.