# Study on Cold Resistance Performance of Composite Subgrade Structure in Seasonal Frozen Regions
## 4 Conclusions  
Regarding the lack of the cold resistance durability of subgrade, especially wet subgrade in seasonal frozen regions, a cold resistance layer consisting of XPS plates and silty clay modified with oil shale waste residue and fly ash was proposed to solve the problem of frost heaving and boiling of subgrade in seasonal frozen regions. By carrying out an outdoor model test, the cold resistance performance of the new type of subgrade structure was evaluated and verified. The valuable results from this research are listed below.  
1. The cold resistance layer, which has a great impact on the temperature distribution inside the subgrade, can form a positive temperature zone which is beneficial to the improvement of cold resistance durability of road structures, including the structural layers above XPS plates.
2. The effective cold resistance area of the cold resistance layer, which is centralized directly beneath XPS plates as the freezing process goes on, tends to stabilize. Thus, key areas should be covered by XPS plates as completely as possible in actual engineering.
3. The cold resistance layer of composite subgrade can effectively raise the temperature of the subgrade 55 cm below the atmospheric contact surface by about 8 \({}^{\circ}\)C, reduce the freezing index 55 cm below XPS plates by more than 14.6%, and maintain an effective positive temperature range beneath XPS plates of no less than 37 cm.
4. After comprehensive analysis, it can be concluded that the cold resistance layer has excellent cold resistance performance which contributes greatly to the improvement of the cold resistance  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Point.** & **3\#** & **4\#** & **5\#** & **6\#** \\ \hline
**FI** & 0 & 114.5 & 153.4 & 134 \\ \hline \end{tabular}
\end{table}
Table 8: Freezing indexes of points inside the subgrade during monitoring period.  
durability of subgrade in seasonal frozen regions and reduces the occurrence of road frost damage. Furthermore, it can prolong road service life, which is in line with the concept of sustainable development.  
In summary, consisting of XPS plates, which have the advantage of extraordinary cold resistance ability, and modified soil, which features outstanding freeze-thaw durability, the cold resistance layer can certainly solve the frost damage problem of subgrade in seasonal frozen regions. This paper provides a basis for the application of a cold resistance layer structure to treat subgrade diseases in seasonal frozen regions.  
Conceptualization, H.W.; methodology, L.H., H.W., and J.Z.; software, L.H.; validation, L.H., H.W., and F.W.; formal analysis, L.H.; resources, F.W., Y.Z., and J.Z.; data curation, L.H. and Y.Z.; writing--original draft preparation, L.H.; writing--review and editing, L.H., H.W., and F.W.; project administration, H.W.; funding acquisition, H.W. and F.W. All authors read and agreed to the published version of the manuscript.  
This research was funded by the National Key R & D Program of China, grant number 2018 YFB1600200, as well as the Science and Technology Project of Jilin Province Transportation Department, grant number 2017 ZDGC6.  
The authors express their appreciation for the financial support of the National Key R & D Program of China, grant number 2018 YFB1600200, as well as the Science and Technology Project of Jilin Province Transportation Department, grant number 2017 ZDGC6. Our thanks go to the editors and reviewers for their efficient work.  
The authors declare no conflict of interest.