Reinforcement Mechanism and Dynamic Response Characteristics of High-Pressure Jet Grouting Piles Behind Bridge Abutments in Binary Strata

To address the excessive differential settlement and the bridge approach bump problem behind bridge abutments in binary strata under cyclic vehicle loading, a highway bridge abutment in western China was investigated as a case study. Through field sampling and laboratory dynamic triaxial tests, the dynamic parameters of the loess-like silt under cyclic loading were calibrated. A three-dimensional dynamic numerical model considering a pile–soil–structure interaction was established. The bridge approach settlement, horizontal displacement, and dynamic responses of abutment pile foundations before and after high-pressure jet grouting reinforcement were compared and analysed. Furthermore, the evolution of reinforcement effectiveness under different axle loads (40–150 [kN]) and vehicle speeds (40–100 [km/h]) was systematically investigated. The results indicate that high-pressure jet grouting can significantly control bridge approach settlement and horizontal displacement, with reductions of 80.5% in settlement and 78.0% in horizontal displacement at the bridge–embankment transition zone. Settlement and horizontal displacements of the pile foundation at shallow depths are effectively suppressed, the stress distribution along the piles becomes more uniform, and stress concentration at the soil–rock interface is notably alleviated. The influence of axle load on reinforcement effectiveness is far greater than that of vehicle speed, with 80 [kN] identified as the critical load for deformation control of the reinforcement system. Within the conventional speed range of 40–100 [km/h], the effect of speed variation on the deformation of the reinforced zone is limited, and the jet grouting reinforcement system maintains a stable control performance. The findings provide a theoretical basis and technical support for the design and maintenance of jet grouting reinforcement against bridge approach settlement in binary strata.