## 1 Introduction  
In the Chinese coastal areas, the economy is developed and more and more highways need to be built. However, in these areas, there are large areas of soft soil which has the characteristics of large porosity ratio, high water content, high compressibility, and low strength. When the highways are constructed on soft soil, the subgrade's large settlement or uneven settlement will occur [1,2]. This is very harmful to subgrade stability. Therefore, the soft soil base should be treated to improve the highway subgrade stability. The loading berm is a treating measure of the soft soil base. The implementation method is as follows. As shown in Figure 1, on both sides of the subgrade, the compacted soil is put on the soft soil base and then the loading berm is formed. The loading berm can inhibit the lateral uplift trend of the soft soil and improve the subgrade stability. Its effectiveness is larger than that of a cutting slope [3]. Due to the good performance of the loading berm, it is widely used for highways in soft soil areas. However, there are also some new cases in the loading berm application. For example, due to the large area of the loading berm, there is not enough construction space in some sections [4]. So, the loading berm cannot be used in these sections. To address this problem, an embedded loading berm (ELB) is proposed in this paper. As shown in Figure 2, the compacted soil is embedded into the soft soil to form the ELB. Compared to the loading berm, the ELB width is smaller. The ELB height can be increased to meet the subgrade stability requirement. The ELB can also inhibit the lateral uplift trend of the soft soil and improve the subgrade stability. Furthermore, the ELB can save construction space and reduce the disturbance effect on the surrounding environment. To date, lots of research has been carried out on the failure modes and stability factors of subgrade in soft soil areas. These studies mainly focused on the influences of loading sperm height and width on the subgrade stability factors. [PERSON] et al. [4] established a stability calculation model of the highway subgrade base on the Mombasa-Nairobi Standard Gauge Railway. They concluded that the loading berm is more advantageous than the gravel pile during the construction period. [PERSON] et al. [5] found that the landslide displacement can be effectively controlled by setting a small loading berm at the slope foot. Through physical modeling and field monitoring, [PERSON] et al. [6] found that subgrade settlement can be effectively diminished by increasing the height of the loading berm. [PERSON] et al. [7] studied the stability of the railway subgrade constructed by fly ash. The study shows that when the subgrade height is 11 m, the loading berm height should not be less than 1.5 m. [PERSON] and [PERSON] [8] proposed the optimization design method of a single-step loading berm and the simplified calculation method of stability factor. They also verified the applicability of the method. [PERSON] et al. [9] deduced the slipping surfaces equilibrium equation considering the cohesion and internal friction angle. Based on the equilibrium equation, a method was presented for determining the reasonable width and height of the loading berm. ISAMU [10] brought out a method to determine the dimensions of loading berm using arc law. Recently, lots of studies were conducted on the subgrade slope stability by the numerical calculation method [11; 12; 13; 14; 15; 16]. In 1975, [PERSON] et al. [17] first applied the strength reduction method to slope stability analysis. [PERSON] et al. [18] researched the stability of a typical three-dimensional slope by the local strength reduction method (LSRM) and explored the feasibility of the local strength reduction method. The results show the local strength reduction method is feasible. Using the strength reduction method, [PERSON] et al. [19] analyzed the stability of the subgrade with loading berm under different working conditions.