## 1 Introduction  
In the process of the continuous improvement of China's highway and railway transportation system, a large number of tunnels have needed to be constructed in the loess strata [1]. However, due to the macropore characteristics of loess soil and its structural features [2; 3], the surrounding rock pressure is different in loess tunnels than that of rock [4; 5]. Several disasters generally occur in the construction of loess tunnels, such as lining cracks, water seepage, tunnel collapses, and even ground cracks in shallow tunnels [6; 7; 8; 9; 10; 11]. The reasons for these disasters have been the inadequate understanding of the surrounding rock and the fact that the surrounding rock pressure used at the design stage of the lining structure was not the same as in the actual model [12; 13; 14; 15]. After excavation, along with the release of surrounding rock stress, the rock around the outline of tunnels deformed into the tunnel [16; 17]. The deformation of the surrounding rock was restrained after the support structure was applied, and the load acted on the support structure, generating the surrounding rock pressure [18; 19].  
For shallow tunnels, calculation methods based on stress transfer and pillar self-weight have been proposed. In deep tunnels, due to the existence of tensile stress at the top of the cavern after excavation, some of the rock masses lose their stability and slip downward and eventually collapse. After collapsing, the rock mass would no longer slide downward and was in a new equilibrium state [20; 21; 22]. Therefore, the surrounding rock pressure in deep tunnels is usually not related to the cover depth. In China, [PERSON]'s theory [23],[PERSON]'s theory [24], and China's Specifications for Design of Highway Tunnels [25] (SDHT) are often used as the calculation method for surrounding rock pressure.  
In [PERSON]'s theory, based on the limit equilibrium theory, the minimum surrounding rock pressure required to maintain the stability of the soil is obtained when the soil above the tunnel is about to fail. In [PERSON]'s theory, the surrounding rock pressure is the weight of the soil between the pressure arching and the lining, and the vertical stress along the arch axis has zero effect on the bending moment at the crown. In SDHT, the surrounding rock pressure is the weight of the soil from the collapse contour to the crown. The surrounding rock on the collapse contour is in a damaged state, and the radial stress is zero.  
[PERSON]'s theory takes soil as load without considering the bearing capacity of tunnel surrounding rock, which is often used in shallow tunnels. The theoretical basis of [PERSON]'s theory and the SDHT are obtained by taking the rock tunnel as the research object. It is thought that when the cover depth is deep enough, the pressure arching could be formed after tunnel excavation. However, there is a lack of systematic research on whether pressure arching is formed after soil tunnel excavation and the formation conditions of pressure arching.  
When the surrounding rock pressure calculation methods of rock tunnels are applied to a soil tunnel, what are the characteristics of the surrounding rock pressure and what are the differences between the surrounding rock pressure of soil tunnels and rock tunnels? It is necessary to analyze the surrounding rock pressure of the existing soil tunnels.  
In this study, through statistical analysis of the surrounding rock pressure of loess tunnels in China, the characteristics of surrounding rock pressure were studied, the applicability of surrounding rock pressure calculation methods in soil tunnels were discussed, and a surrounding rock pressure calculation method based on statistical analysis was proposed.