Abstract: In collapsible loess regions, backfilling utility tunnel foundations with compacted loess can generate sig? nificant additional loads, thereby exacerbating the collapsible deformation of the underlying loess upon water infiltration. To address this issue, field immersion tests and fluid-solid coupling numerical simulations were conducted to investigate the anti-seepage and load-reduction effects of a cement-soil bearing plate with high rigidity and low permeability installed at the top of the utility tunnel. The results demonstrate that the cement-soil bearing plate significantly mitigates the impact of water infiltration on the underlying loess through its "anti-seepage effect" and "cantilever effect." Under extreme rainfall conditions, the average saturation of the underlying loess layer decreased by 9.1%. Due to its high stiffness, the cement-soil bearing plate functions as a "bearing plate," reducing the collapsible deformation of the foundation to 7.2 cm, approximately 40% less than that observed in conventionally backfilled utility tunnel sections. Orthogonal fluid-solid coupling numerical simulations indicate that when the bearing plate is constructed with C25 reinforced concrete, with an extension width of 1.5 m and a thickness of 25 cm, the settlement at the center of the utility tunnel base is minimized (5.005 cm). It is recommended that 5.0 cm be adopted as the allowable settlement value for utility tunnel foundations.