The subgrade serves as the foundation of road construction, typically involving a significant amount of earthwork during its establishment. However, in coastal and desert areas, soil sources are often scarce. Local soil extraction significantly damages cultivated land, impacting the local ecological environment. Transporting soil over long distances inevitably raises construction costs. Fortunately, these regions often feature abundant fine sand distribution, presenting an opportunity to utilize it as subgrade filler in coastal regions. This review comprehensively introduces the properties of fine sand as a raw material, its engineering applications, and the associated construction technologies. It emphatically discusses the road use characteristics and treatment technology of fine sand filler and puts forward a prospect combining the characteristics and development trends of fine sand so as to provide a new perspective and basic material for the application of fine sand in the subgrade. To foster the adoption of fine sand in subgrade construction, it is recommended to advance research on the evaluation and treatment of fine sand foundations, analyze its suitability and structural behavior as a filler, and refine construction methodologies and quality control measures specific to fine sand subgrades.

This research addresses the characteristics of soft soil subgrades treated by soilbags filled with excavated clayey soil. We evaluated of the strength and deformation modulus of soilbags containing excavated soil using unconfined compression tests. In addition, the drainage consolidation characteristics of soilbag-treated subgrades were investigated via model consolidation tests. Furthermore, a practical application included the construction of a 100 m-long rural road subgrade with these soilbags. The field test and numerical simulation results included the surface settlement and pore water pressure during and after construction to validate the effectiveness of the soilbag treatment for soft soil subgrade. The results show that the soilbags significantly enhanced both the strength and deformation modulus of the soft soil, which met the design requirements after the soilbag treatment. The drainage attributes of the soilbag treatment were also found to support the consolidation process of the soft soil subgrade effectively. Notably, the pore water pressure diminished rapidly during the construction interval, which is beneficial to reducing the post-construction settlement. The settlement uniformity of the subgrade is good verification of the superiority of the soilbag-treated subgrades.