**5. Conclusions**

In this paper, areas that suffer serious highway waterfall ice hazards (Tongchuan-Huangling expressway) were chosen to conduct ground water monitoring for 2.5 years. The relationship between the ground water level change and waterfall ice hazards is revealed. After that, the gradation test and penetration test of the aquifer soil, and the freezing test of typical saturated fine-grained soil and coarse-grained soil were conducted. Following this, the mathematical model of investigating waterfall ice was established. Finally, the formation mechanism of highway waterfall ice was discussed. The following primary conclusions can be drawn:


**Author Contributions:** Conceptualization, Z.Z., J.L., S.Z., and H.Z.; data curation, J.L., S.Z., S.Q., and H.Z.; funding acquisition, Z.Z.; investigation, J.L.; methodology, J.L., S.Z.; writing-original draft, J.L.

**Funding:** This work is financially supported by the National Key R&D Program of China (no. 2016YFC0802203-8).

**Conflicts of Interest:** The authors declare no conflicts of interest.

#### **Appendix A Appendix A**

*Sustainability* **2019**, *11*, x FOR PEER REVIEW 19 of 21

**Figure A1.** Temperature and frozen depth change of Tongchuan-Huangling expressway during winter 2014–2015. **Figure A1.** Temperature and frozen depth change of Tongchuan-Huangling expressway during winter 2014–2015.
