# Durability-Aimed Design Criteria of Cement-Stabilized Loess Subgrade for Railway
## 5 Conclusions  
1. The effects of cement dosage and compaction level on the fatigue characteristics of cement-stabilized loess were investigated in this study. Taking into account the most unfavorable conditions, the strength fatigue reduction coefficient of 0.26 was obtained.
2. The effect of wet-dry cycling on the strength reduction of cement-stabilized loess was investigated in this study. The results show that the strength decreases continuously with the increase of the time of wet-dry cycling, and the strength became to be stable after 15 times. Taking into account the most unfavorable conditions, the strength reduction coefficient of cement-stabilized loess under wet-dry cycling of 0.40 was obtained.
3. The effect of freeze-thaw cycling on the strength reduction of cement-stabilized loess was investigated in this study. The results show that the strength decreases continuously with the increase of the time of freeze-thaw cycling, and the strength became to be stable after 12 times. Taking into account the most unfavorable conditions, the strength reduction coefficient of cement-stabilized loess under freeze-thaw cycling of 0.30 was obtained.
4. The dynamic stress level of the railway subgrade was analyzed in this study. Moreover, it was obtained that the dynamic stress \(\sigma_{\mathrm{dmax}}\) of subgrade bottom is 50 kPa, and the dynamic stress \(\sigma_{\mathrm{dmax}}\) of the embankment below the subgrade is 25 kPa.
5. The 7-day strength design criteria were presented based on durability: 7-day unconfined compressive strength of cement-stabilized loess saturated with water of the subgrade bottom should be higher than 1100 kPa, and 7-day unconfined compressive strength of cement-stabilized loess saturated with water of embankment below the subgrade should be higher than 550 kPa.  
F.W.: Conceptualization, Methodology, Formal analysis, Writing--Reviewing and Editing. W.P.: Methodology, Investigation, Data curation and Writing--original draft. L.H.: Conceptualization, Writing--original draft and Validation. Y.J.: Resources, Funding acquisition and Supervision. X.Q.: Visualization. All authors have read and agreed to the published version of the manuscript.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{\multirow{2}{*}{**The Grade of Railway**}} & \multicolumn{2}{c}{**7-Day Unconfined Compressive Strength Saturated with Water (kPa)**} \\ \cline{2-3}  & **Subgrade Bottom** & **Embankment Below the Subgrade** \\ \hline Passenger and freight railway & & \\ Inter-city railway & & \\ High-speed railway, & & \\ Heavy-haul railway & & \\ \hline \hline \end{tabular}
\end{table}
Table 9: The strength design criteria of cement-stabilized loess.  
**Funding:** This research was funded by the Science and Technology Project of Shaanxi Provincial Department of Transportation (No. 18-02K and No. 19-27K), the Scientific Research of Central Colleges of China for Chang'an University (No. 300102218212), and the Science and Technology Project of Jilin Provincial Department of Transportation(2017 ZDGC-7).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Acknowledgments:** This research was supported by the Science and Technology Project of Shaanxi Provincial Department of Transportation (No. 18-02K and No. 19-27K), the Scientific Research of Central Colleges of China for Chang'an University (No. 300102218212), and the Science and Technology Project of Jilin Provincial Department of Transportation (2017 ZDGC-7). The author gratefully acknowledges its financial support. Thanks to editors and reviewers for their efficient work.  
**Conflicts of Interest:** The authors declare no conflict of interest.