In jointless bridges, expansion joints are eliminated. Consequently, girder deformations caused by thermal expansion and contraction are only partially absorbed by the approach slab, while the remainder is transmitted through this slab into the backfill and the connecting road. Distress in the approach slab is a common issue that adversely affects the service performance of jointless bridges. In certain engineering applications, an inclined approach slab buried within the backfill underneath the connecting road-referred to as a buried inclined approach slab (BIAS)-has been employed. The structural response of both the jointless bridge and its approach slab depends strongly on the interaction among the approach slab, backfill, and connecting road. To achieve a more favorable stress distribution in the backfill and connecting road, shear projections are proposed for installation on the upper surface of the BIAS. To clarify the interaction mechanism of the BIAS with shear projections, backfill and connecting road system, the system was designed and constructed. The absolute displacement of the approach slab, the relative displacements between the girder and approach slab, and the soil pressure at the approach slab end face were monitored in the field. A finite element model (FEM) of this system was then developed in PLAXIS and verified using the monitored data. The results demonstrate that excluding the connecting road causes plastic failure and substantial deformation in the backfill. Conversely, when the connecting road is included, the backfill maintains better integrity; even though the deformation zone widens, deformations are much smaller, plastic failure does not take place, and pavement surface roughness is therefore improved. In addition, shear projections strengthen the contact interaction between the BIAS upper surface and the connecting road materials. This improvement results in a slight increase in structural stiffness and peak force, a considerably enlarged longitudinal deformation zone under push displacement, and enhanced pavement smoothness.

Geosynthetic reinforced soil integral bridges (GRS-IBs) combine a jointless structural system with reinforced backfill mechanically connected to the abutment. The K57+125 highway overpass in Quanzhou, China, is a GRS-IB, modified from a jointed bridge. This study investigates its design modification, stability verification, and economic performance. After conversion from the original jointed bridge to the GRS integral system, the main-girder prestressing arrangement was redesigned, reducing the number of tendon groups from five to four. Internal stability verification showed that the maximum reinforcement tensile force was 13.84 kN and the minimum pullout safety factor was 96.05, while the reduced ultimate bearing capacity and the reduced dead-load bearing capacity corresponding to 1% vertical strain both exceeded the applied vertical pressure of 97.59 kPa. The sliding and overturning safety factors were 2.18 and 5.92, respectively. Compared with the original bridge scheme, concrete and prestressing-strand consumption decreased by approximately 36% and 12.76%, respectively, while reinforcing-steel consumption increased by approximately 18%. The estimated initial construction cost was nearly 10% lower. These results demonstrate the structural feasibility and economic potential of the adopted GRS integral bridge scheme.