Experimental investigation on the impact resistance of bridge piers against debris flow with a prefabricated composite structure

• The varying impact of solid materials in debris flows was stimulated. • The debris flow resistant of bridge pier is enhanced by the proposed composite structure. • Its mechanism is associated to divert effect and energy absorption capability. This study presents a self-designed prefabricated composite structure, aimed at enhancing the resistance of bridge piers to debris flows. Drawing on the engineering prototype of the ‘8.17’ debris flow disaster at the Dalei gully Bridge in Mianyang, Sichuan, China, the effectiveness of prefabricated composite structure was examined through simulated model tests, and compared with that of steel casing protection. The results demonstrate that the prefabricated composite structure effectively diverted the solid materials within debris flows, thereby reducing their impact on bridge piers. In comparison with unprotected bridge piers, the application of the prefabricated composite structure reduced the peak impact force by 86.4%∼97.3%, the pier top displacement by 96.1%∼98.5%, the bending moment by 82.2%∼90.6%, the axial force by 91.3%∼94.5%, respectively. These effects were superior to those of steel casing protection, primarily attributed to the design of flexible buffer units and the utilization of recycled tiers. An analysis of pressure distribution and energy absorption reveals that, the prefabricated composite structure resulted in a more uniform pressure distribution and lower energy impact on the pier body during debris flows. Compared with unprotected bridge piers, the implementation of the prefabricated composite structure reduced the top peak frequency spectral amplitude (PFSA) by 56%∼72%, the top peak Hilbert energy spectrum (PHES) by 62.31% ∼98.91%, and the top peak marginal spectrum amplitude (PMSA) by 90%. These findings suggest that the proposed prefabricated composite structure can be an effective protective measure for improving the force resistance of bridge piers against debris flows.