Dynamic Response of Concrete Bridge Piers Under the Impact of Dry Granular Flow with Giant Boulders: A Scaled Model Study on the Force Mechanism of Boulders

Dry granular flow disasters occur frequently in mountainous areas. The impact of dry granular flow with giant boulders poses a serious threat to the stability of concrete bridge piers. In this study, physical model tests were combined with PFC-FLAC coupled numerical simulations to investigate the dynamic response of concrete bridge piers under the impact of dry granular flow with giant boulders. The force model of the giant boulders considering the boulder size (S) and the distance in front of the slope (L) was analyzed. The proposed method was validated through a dual comparison of the peak acceleration at the pier top (with a relative error of 30%) and the macroscopic accumulation morphology. The results showed that the method can effectively simulate the impact process of dry granular flow with giant boulders on bridge piers. It provides methodological support for parametric studies of the pier impact response at different boulder sizes. The acceleration time histories and accumulation morphologies obtained from the numerical simulations agreed well with the test results. The peak impact force on the pier in the X direction first decreased and then increased with the increase in boulder size, and the peak impact force was 4.89 × 103 N when S = 15 cm. It first increased and then decreased with the increase in the distance in front of the slope; the peak impact force reached 5.04 × 102 N when L = 0.15 m, and the peak time was prolonged. The acceleration at the pier top increased with the increase in boulder size and decreased with the increase in the distance in front of the slope. The force analysis of the giant boulders indicated that the density of the dry granular flow and the boulder size are the key parameters controlling the forces acting on the boulders. The supporting force and the drag force increased with the increase in the density of the dry granular flow, and the friction force decreased with the increase in density. The gravity and the supporting force of the boulders increased with the increase in boulder size. This study reveals the influence laws of boulder size and the distance in front of the slope on the impact of dry granular flow on bridge piers. The findings can provide a theoretical basis for the impact-resistant design of bridges and disaster prevention in mountainous areas.