# The Application of Fine Sand in Subgrades: A Review
## 4 Application of Fine Sand Subgrade Engineering
### Application of Sand-Filled Subgrade  
The uniqueness of sand-filled subgrades lies in the fact that the core filling material is sand, rather than the traditional notion of fine-grained clay. Due to the unique characteristics of the filling material, designers and construction personnel must carefully consider the impacts on the structural system of sand-filled subgrades.  
The engineering practices of typical sand-filled subgrades in China are summarized in Table 5. Compared to embankments and stockpiles formed by sand accumulation, sand-filled subgrades exhibit significant differences in aspects such as filling height, types of lateral confinement, drainage design, construction techniques, and quality inspection. For example, while coastal embankments serve as water barriers where slope stability must be carefully verified, such considerations are less relevant in the design of sand-filled subgrades.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Project Name** & **Material Characteristics** & **Slope Protection** & **Sealing Structure** \\ \hline \multirow{3}{*}{Shenshan Expressway [74]} & 5\% natural moisture, 3–5\% clay content & Edge width \textgreater{} 1.6 m, 30 cm & \multirow{3}{*}{Aeolian sand} \\  & Low powder and clay content, lacks stickiness, 1–4\% natural moisture & Wrapped clay with a thickness of 2.0 m & \multirow{3}{*}{80 cm gravel or gravel soil} \\  & Fewer silt particles, lacks stability, forms slurry when wet, loose when dry & Fill subgrade sides with cohesive soil, center with windblown sand, roll simultaneously & High-strength materials such as weathered sandstone and stone slag, with a cross slope of 2\% for road arches \\ \cline{2-4}  & Minimal cohesive and plastic properties due to high sand & Cohesive soil edging, outer slope 1:1.5, inner slope 1:1, & Gravel soil \\  & and low silt content & 2.0 m thick & \\ \cline{2-4}  & Liaoning Central Ring Expressway [78] & Contains few silt particles, optimal moisture 10–15\% & Fill subgrade sides with cohesive soil for edge wrapping & Mountain soil, weathered rock, crushed stone soil, and stone slag, with a thickness of 80 cm \\ \cline{2-4}  & & Wrap clay for windblown & \multirow{3}{*}{-} \\  & Fine sand, without & sand and fine-grained soil, slope 1:2 to 1:3. Fill subgrade & \\ \cline{2-4}  & & directly, slope \(\leq\) 1:3 & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Overview of typical sand-filled subgrades with aeolian sand.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Project Name** & **Sand Source** & \
\begin{tabular}{c} **Material** \\ **Characteristics** \\ \end{tabular} & **Slope Protection** & **Sealing Structure** \\ \hline \multirow{3}{*}{Suiyuezhong Expressway [80]} & Alluvial sand on the & Fine sand &
\begin{tabular}{c} Subgrade enveloped in 6\% \\ lime soil wrapping, 25 cm \\ thick layers with fine sand \\ filled between \\ \end{tabular} & Gravel \\ \cline{2-4}  & & & \\ \hline \hline \end{tabular}
\end{table}
Table 5: Overview of typical sand-filled subgrades.  
blowing subgrades, is discussed, underscoring its relevance and effectiveness in practical engineering applications.