Investigation on the Impact Resistance of Bridge Piers with a Reinforced Concrete Composite Structure Against Debris Flow

Round-ended bridge piers are specifically utilized for high-speed railways in mountainous areas. However, the protective measures for such piers under debris flow remain limited, especially regarding the various components in the debris flow. This study introduces a reinforced concrete (RC) composite structure to improve the debris flow impact resistance of round-ended piers and investigates the impact from three different components of debris flow, including the bulk impact of slurry, collisions of large boulders, and abrasion of rock fragments. The results indicate the following: (1) The RC composite structure effectively mitigated the macroscopic damage from all types of debris flows. This structure significantly decreased gravel accumulation in the front of the pier body and reduced the size of scouring pits. These effects are superior to those of steel casing protection. (2) The RC composite structure significantly reduced the pier top displacement and pier body bending moments and optimized the pressure distribution on the pier body. The peak pressure reduction reached 95.7%, 88.4%, and 97.7% under three different debris flows. These effects were more pronounced than those under steel casing protection, for which the corresponding reductions were 18.2%, 70.9%, and 69.7%. (3) The RC composite structure effectively absorbed impact-induced vibrations and weakened shock effects on the upstream face, exhibiting superior capabilities compared with those of steel casing. The RC composite structure showed particularly outstanding performance in gravel-dominated debris flows. Ultimately, the RC composite structure could be an effective technique for enhancing the resistance of round-ended bridge piers against debris flows.