## 6 Results  
This study presented an innovative active artificial heating method for addressing the issue of the frost heaving of embankments in cold regions. A DE-GSHP was designed and developed to meet space and performance requirements. An experimental test was conducted to evaluate its heating performance during cold seasons. Based on the obtained results, the main achievements of this article can be summarized as follows:  
1. Active heating was essential to maintaining the thermal stability of the embankments in extremely cold regions. The application feasibility of the existing heating methods, including boilers, electric heaters, solar thermal collectors, and GSHPs, in embankment engineering, in terms of the location conditions along railways, initial costs, and efficacy, etc., were compared. Subsequently, the GSHP technique was appropriate for embankment heating due to its high heating capacity and flexibility with the ambient temperature.
2. A prototype for testing the DE-GSHP's performance was successfully constructed. Through extensive experimentation, the performance parameters, such as the heat-supplying temperature, heat-absorbing temperature, and the COP, indicated that the DE-GSHP was highly efficient for embankment heating. The heat-supplying temperature in cold seasons was automatically controlled at 30, 45, 60, and 75 \({}^{\circ}\)C, which corresponded to negative heat-absorbing temperatures below 0 \({}^{\circ}\)C that facilitated geothermal energy utilization. In addition, the novel GSHP consumed low energy with a COP value above 3.5, while high COP values were acquired for low predetermined heat-supplying temperatures. Therefore, the novel technique was preferred during the construction and maintenance of high-speed railways and expressways in extremely cold regions due to it preventing frost heaving in embankments.
3. The results of numerical computations demonstrated that, under the artificial heating effect, regions of significant warming and cooling were formed in the roadbed and in the foundation beside the foot of the slope, respectively, which indicated that the heat pump could realize an efficient collection, transformation, and transfer of geothermal energy. The freezing depth of the roadbed under artificial heating conditions was significantly reduced, the melting process took place earlier, and there was no bidirectional thawing phenomenon.
4. There are operational restrictions on this device. Due to the solidification of lubrication oil, the compressor performance is limited by the ambient conditions during the operation of the DE-GSHP. More specifically, it cannot operate properly in ambient temperatures below \(-40\)\({}^{\circ}\)C. Under this severe condition, thermal insulation should be adopted.  
Figure 14: Variation pattern of freezing depth (Y = 20 m).  
**Author Contributions:** Conceptualization, M.C. and T.H.; methodology, M.C.; validation, M.C. and T.H.; data curation, Y.Z.; writing--original draft preparation, M.C.; writing--review and editing, Y.Z. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was supported by the Natural Science Foundation of Hebei Province, China (E2020210044).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.