## 1 Introduction  
Pernafrost is defined as a rock and soil mass containing various substances that exist continuously for two years or more at or below 0 \({}^{\circ}\)C [1]. China is the third largest frozen soil country in the world. The permafrost area is about 2.15 \(\times\) 10\({}^{6}\) square kilometers, accounting for 22.4% of China's total land area [2, 3]. Pernafrost is mainly distributed in the Qinghai Tibet Plateau at high altitude and the Greater and Lesser Khingan Mountains at high latitudes [4, 5]. As one of the most important forestry bases in China, the Great Khingan Mountains are covered by a large area of virgin forests with rich vegetation types [6]. Therefore, the Great Khingan Mountains permafrost belongs to the high latitude forest region permafrost, with a total area of about 0.39 \(\times\) 10\({}^{6}\) square kilometers [7, 8]. Pernafrost is characterized by poor thermal stability, sensitivity to climate warming, and strong hydrothermal activity [9, 10]. In the context of global warming, permafrost is gradually deteriorating [11], which will lead to the rise of underground temperature, the increase of seasonal active layer thickness, and the increase of greenhouse gas emissions [12, 13]. Moreover, the degradation of permafrost will also lead to ground settlement and deformation, which will seriously affect the stability of engineering structures [14]. In the forest region of the Great Khingan Mountains, the cold region ecosystem formed by the interaction of permafrost and vegetation is more vulnerable to damage due to environmental changes [15, 16]. Vegetation cover will change the energy exchange process in the soil layer and directly affect the hydrothermal state of permafrost. [PERSON] et al. [17] proposedthat vegetation can effectively slow down the degradation of permafrost caused by climate warming by regulating the surface freeze-thaw cycles of permafrost. In order to reflect the influence of vegetation on surface heat transfer more accurately, [PERSON] et al. [18] proposed an improved productivity simulator for the northern ecosystem and further studied the role of vegetation in the process of soil surface freezing and thawing. [PERSON] et al. [19] found that revegetation can effectively improve the permafrost stability of degraded grassland in the Qinghai-Tibetan Plateau and enhance the service functions of alpine grassland ecosystems. [PERSON] et al. [20] studied the impact of tundra vegetation type on topsoil temperature in central Spitsbergen. [PERSON] et al. [21] studied the influence of freeze-thaw erosion on the stability of steep slopes with high ice content in the Great Khingan Mountains. [PERSON] et al. [22] studied the temperature load mode of a railway bridge in the permafrost region of the Qinghai-Tibet railway. [PERSON] et al. [23] developed an algorithm for numerical prediction of frost heaving and thaw settlement of a railway embankment on permafrost in Central Yakutia. However, these engineering activities did not take into account the factors of vegetation cover. It can be seen that in the Greater Khingan Mountains forest region, scholars have studied the interaction between vegetation and permafrost, mainly focusing on the influence of vegetation on the active layer of permafrost. However, under the condition of vegetation cover, there are relatively few studies on the influence of engineering construction, especially road engineering construction, on permafrost. Based on the road project of National Highway 332 in the Great Khingan Mountains permafrost forest region, this study analyzed the influence of vegetation cover on the settlement behavior of the permafrost subgrade by means of field observation, experimental testing, and numerical simulation.