Abstract:The low embankment on the stable Quaternary deposits that meets the requirements of the general subgrade has been deformed and destroyed in operation. Based on the saturated and unsaturated seepage theory and the dual-stress variable strength theory of FREDLUND unsaturated soil, the calculation model before and after the embankment filling is established, and the stability of the Quaternary deposits before and after the embankment filling of a road project in Gouxi Village, Langzhong City, Sichuan Province is analyzed. The research results show that the geological conditions of Quaternary deposits where the route passes are simple, and the original slope also remains stable under the most unfavorable rainfall conditions, and the embankment filling height is only 4 m, which meets the requirements of general subgrade. Under the most unfavorable rainfall conditions, the stability coefficient of the accumulation embankment decreases with the rainfall process. When the rainfall reaches 11 hours, the stability coefficient is less than 1.0, and the embankment is damaged, which is consistent with the phenomenon of instability and failure of the subgrade. In the process of highway construction in mountainous area, although filling low embankment on stable quaternary accumulation body meets the requirements of subgrade design code for general subgrade and does not need to be checked separately, its stability will continue to decrease under the action of long-term rainfall, which is likely to cause instability and failure. Therefore, the stability under long-term rainfall should be checked in engineering design and construction to ensure the safety of the project.