## 7 Conclusions  
This study conducted a comprehensive experimental investigation into the anisotropic swelling behavior of expansive soils and developed predictive methodologies to estimate earth pressures considering this inherent anisotropy. Based on the results and findings, the following conclusions were drawn:  
(1) Modified oedometer testing quantified clear anisotropy in expansive soil, with a maximum vertical swelling strain 1.71 times that of the horizontal direction. The swelling pressures were also directionally dependent, and the vertical swelling pressure was 1.57 times that of the horizontal one. (2) A nonlinear elastic constitutive model was proposed incorporating vertical and horizontal elastic moduli with respect to matric suction to characterize swelling anisotropy. Three key elastic moduli were determined from the test data. (3) The elastic moduli decreased nonlinearly with saturation and increased under higher confinement, exhibiting strong dependence on stress state and suction. The differences between the horizontal and vertical moduli quantify the macroscale manifestation of microstructural anisotropy. (4) Simple predictive equations were developed to estimate unsaturated elastic moduli from saturated conditions via normalization. Validation affirmed the use of a constitutive model and predictive techniques as useful engineering tools for earth pressure assessments that consider expansive anisotropy. In conclusion, these findings provide an improved understanding of more realistic characterization and utilization of expansive soils in geotechnical applications by properly accounting for their inherent anisotropic behavior. However, deviations between the \begin{table}
\begin{tabular}{l c c c c c c c c c} \hline \hline \multirow{2}{*}{**Test ID**Indices**} & \multicolumn{2}{c}{\(R^{2}\)} & \multicolumn{2}{c}{**RWI**} & \multicolumn{2}{c}{**MAAPE (\%)**} & \multicolumn{2}{c}{**RMSE**} & \multicolumn{2}{c}{**MAE**} \\ \cline{2-10}  & **ANI** & **ISO** & **ANI** & **ISO** & **ANI** & **ISO** & **ANI** & **ISO** & **ANI** & **ISO** \\ \hline OVS-0 & 0.9899 & 0.9898 & 0.9239 & 0.7610 & / & / & 2.6975 & 8.6487 & 1.99 & 7.45 \\ OVS-12.5 & 0.9966 & 0.9712 & 0.9118 & 0.7788 & 9.9 & 20.4 & 2.7427 & 7.7028 & 2.35 & 6.86 \\ OVS-25 & 0.9858 & 0.9761 & 0.8513 & 0.6464 & 12.2 & 30.8 & 4.4998 & 14.1332 & 3.96 & 13.52 \\ OVS-50 & 0.9410 & 0.8940 & 0.7553 & 0.6935 & 13.4 & 21.9 & 7.0124 & 12.9584 & 6.46 & 11.63 \\ OVS-100 & 0.9362 & 0.9038 & 0.7978 & 0.6529 & 11.8 & 21.6 & 8.3822 & 17.4199 & 7.32 & 16.81 \\ OHS-0 & 0.9816 & 0.9882 & 0.8873 & 0.5856 & / & / & 5.3509 & 30.2147 & 4.27 & 27.86 \\ OHS-12.5 & 0.9828 & 0.9751 & 0.8898 & 0.6022 & 16.7 & 47.5 & 5.2837 & 29.7645 & 4.63 & 27.77 \\ OHS-25 & 0.9746 & 0.9549 & 0.8055 & 0.5631 & 22.7 & 54.3 & 11.1098 & 41.2384 & 10.06 & 38.76 \\ OHS-50 & 0.9850 & 0.9193 & 0.8520 & 0.5633 & 18.6 & 50.7 & 9.3792 & 46.3975 & 8.65 & 44.06 \\ OHS-100 & 0.9464 & 0.8835 & 0.7976 & 0.5681 & 17.9 & 43.2 & 15.3981 & 46.4962 & 13.52 & 45.22 \\ \hline \hline \end{tabular} Note: ANI: estimation using the proposed method (anisotropic consideration); ISO: estimation using [PERSON]’s nonlinear elastic model (isotropic consideration).  
\end{table} 
Table 7: Summary of the calculating statistical indices for all test series. measured and predicted lateral pressures were found to be relatively large at higher stress states; this proposed model and method are suggested to be used in designing light structures with lateral confinement at shallow depths. In addition, studies based on in situ soils and soils from other locations are necessary to further validate the methodology presented in this paper, and studies on swelling in an angular direction with respect to the direction of compaction should also be carried out. Conceptualization, Z.L. and R.Z. ; methodology, Z.L. and R.Z. ; validation, Z.L., T.L. and C.H. ; formal analysis, Z.L. and T.L. ; data curation, Y.Z. and C.H. ; investigation, Z.L. and Y.Z. ; writing--original draft preparation, Z.L. and Y.Z. ; writing--review and editing, Z.L., T.L.