## 8 Conclusions  
In this paper, the national highway G331 Shiwei-Labudalin highway permafrost subgrade K60 + 230 section is the object of study. Through the monitoring of field data,  
Figure 21: Permafrost table at different locations for subgrades with different block-stone particle sizes. the establishment of the permafrost area of the ordinary subgrade temperature field and the block-stone subgrade temperature field finite element model, the study of different working conditions of the block-stone subgrade cooling, and based on the prevention and control of related diseases to give a reasonable proposal. The main conclusions are as follows:  
1. During the monitoring of the four freeze-thaw cycles, the temperature of the soil at different depths showed cyclic changes, showing obvious seasonal characteristics, with the shallow soil layer of the subgrade being significantly affected by the air temperature and the soil at deeper depths responding less to changes in atmospheric temperature, due to the fact that it did not undergo a freeze-thaw cycle and was maintained in a relatively stable negative temperature state. The permafrost table in the lower part of the subgrade at all locations has decreased to different degrees, with the medial divider decreasing by 0.5 m, the left toe of the slope by 0.5 m, the right toe of the slope by 0.5 m, and the right natural hole by 2 m, which is the main reason for the uneven settlement of the subgrade. The temperature change in the soil under the subgrade has a hysteresis phenomenon with increasing depth, and the hysteresis effect in the cold season is smaller than that in the warm season. Due to the sunny-shady slope effect, the lateral difference in subgrade temperature is large. The heat gains and losses in the medial divider and the right natural hole both show heat absorption; the medial divider is more affected by external ambient temperatures as well as engineering disturbances. 2. According to the numerical simulation results of the ordinary permafrost subgrade, the temperature field of the subgrade shows an asymmetry of right-high and left-low due to the sunny-shady slope effect. The permafrost table decreased to different degrees at all locations during the simulation. The average rate of decrease in the permafrost table at the medial divider, the left toe of the slope, the right toe of the slope, and the natural ground surface during the 15-year period was 0.38 m/a, 0.31 m/a, 0.37 m/a, and 0.15 m/a, respectively. The decrease in the permafrost table at the medial divider was the fastest in the past few years. 3. Block-stone subgrades can effectively lift the permafrost table and better maintain the stability of the soil beneath the subgrade. Replacement 1 m block-stone subgrade lifts the permafrost table better compared with the ordinary subgrade top surface, the medial divider, the left toe of the slope, the right toe of the slope, and the natural ground surface lifting 1.05 m, 1.32 m, 1.49 m, and 0.49 m, respectively. The increase in the thickness of the replacement block stone can reduce the temperature of the lower soil; the thickness of the block stone increased sequentially from 1 m to 4 m, and the temperature of the soil at a depth of 5 m decreased by 0.1 \({}^{\circ}\)C, 0.31 \({}^{\circ}\)C, and 0.26 \({}^{\circ}\)C, respectively. In the construction of road projects in warm permafrost areas, priority should be given to the use of replacement block-stone subgrades to effectively protect the permafrost. The simulated thickness of the replacement block-stone is 1-4 m, and the cooling effect is best when the thickness is 4 m; the simulated block-stone particle size is 4-15 cm, and the cooling effect is best when the block-stone particle size is 6-8 cm. Increasing the particle size of the block stone too much may affect other physical parameters of the block-stone layer, which may weaken the protection of the block-stone subgrade against the underlying permafrost. Conceptualization, W.S. ; writing-original draft preparation, W.S. and Y.L.