In mountainous regions, high fill slopes and bridge structures are common due to topographical limitations, often leading to difficulties in transporting prefabricated bridge components. To address this situation, this paper proposed arranging a sunken precast beam yard on high fill roadbeds. The research analyzed the primary factors of roadbed settlement and deformation, applied multiple deformation control measures to manage the deformation of high fill roadbeds and the precast beam yard, and characterized their deformation through a three-dimensional numerical model analysis. The results show that replacing the lower soil layer with poor physical properties with a filler layer with better physical properties can effectively reduce the uneven settlement of the precast beam yard. After implementing settlement control measures, the overall settlement of the precast beam yard is approximately 20 mm, with uneven settlement limited to only 3 mm. The construction impact range of the precast beam yard on the underlying fill layer is similar to that of the beam yard area.