Abstract:

The utilization of excavated soil and fly ash to produce foamed lightweight soil (FLS-FE), and its application in subgrade filling in soft soil areas or the control of uneven settlement at the transition zones between strong and weak subgrades, are a green, environmentally friendly, and effective treatment solution. Guided by concept, a series of laboratory tests were conducted to investigate the variation patterns in fluidity, water absorption, and unconfined compressive strength of FLS-FE at different mixing ratios. Further wet-dry cycling and freeze-thaw cycling experiments were implemented to reveal the evolution patterns of FLS-FE under long-term service conditions. The test results indicate that the fluidity of FLS-FE is significantly influenced by the content of excavated soil and fly ash, while fly ash and hydrated lime can reduce its water absorption. The dry density correlates with compressive strength changes. As the excavated soil content increases, the compressive strength of FLS-FE decreases significantly. However, the incorporation of both fly ash and hydrated lime can effectively enhance its strength and toughness. In particular, adding 4% hydrated lime for alkali activation to stimulate the reactivity of the solid waste molecules can increase the compressive strength by 43.9%.In terms of durability, when incorporating excavated soil alone at ≤50% dosage, the strength loss after 20 cycles does not exceed 30%. At a 60% dosage, the strength loss of FLS-FE reaches 46% under wet-dry cycling and 40% under freeze-thaw cycling. However, The addition of fly ash can notably mitigate this strength degradation. After introducing hydrated lime to create an alkaline environment, the mass loss of FLS-FE remains below 13% after wet-dry cycles and below 12% after freeze-thaw cycles, with durability coefficients consistently exceeding 70%. Based on the experimental findings, it is recommended that the content of excavated soil in FLS-FE for subgrade filling should not exceed 50%; the overall solid waste utilization rate can reach 60% by incorporating fly ash, and adding 4% hydrated lime can maximize the performance enhancement of FLS-FE.

Key words: excavated soil, fly ash, hydrated lime, physical-mechanical properties, durability, foamed lightweight soil