Abstract: Stabilizing soft soil roadbeds in mountainous areas is a difficult problem in highway engineering. The pavement cracks on a coastal expressway soft soil section along the mountain side are observed. Combining with the relevant engineering data, the stability of the soft soil roadway is back analyzed at a critical section by using the Plaxis finite element method and the influence of different soft soil treatment measures on the subgrade stability is evaluated. The results show that the geological conditions of the soft soil section near the mountain are not uniform in longitudinal and transverse directions, and the potential sliding surface is more easily induced by the climate and the rainfall, which causes the phenomenon of subgrade destabilization. For the secondary reinforcement of the soft soil subgrade with complicated geological conditions, mitigation measures such as cement mixing columns, anti-slide caissons and high-pressure jet grouting columns can avoid and minimize the subgrade sliding hazards. The method of anti-slide caisson plus high-pressure jet grouting columns can effectively reduce the settlement of the subgrade and improve the stability of subgrade with the limited land use, which can provide reference for the future mitigations of the soft soil subgrade.

Key words: Soft Soils, Coastal Expressway, Road Section Along the Mountain, Finite Element Strength Reduction Method, Anti-Slide Caisson