Dynamic response characteristics of bridges under the impact of debris flows in mountainous areas

Debris flows pose a significant geological hazard, impacting economic development, transportation infrastructure, and the ecological environment in mountainous regions. To investigate the movement and disaster-causing characteristics of debris flows along the Jiuzhai-Mianyang Expressway, a series of scaled flume experiments were conducted to simulate their impact on bridge piers. These experiments, informed by field investigations of debris flow gullies along the Jiuzhai-Mianyang Expressway, examined the effects of debris flow density, flume angle, and the distance between the debris flow outlet and the bridge pier. The study introduced the Froude number to develop a calculation model for debris flow impact forces. Results showed flow velocities ranging from 0.75 to 6.14 m/s, debris flow depths from 2.7 to 13.4 cm, and maximum impact forces between 1.5 and 74.76 kPa. Flume angle was identified as a critical factor influencing viscous debris flow velocity. Impact patterns varied with flow conditions and fluid properties, exhibiting behaviors such as splashing, climbing, and flowing around obstacles. Furthermore, a refined hydrodynamic model for debris flow impact force, based on experimental data and existing literature, revealed a power function relationship between impact force and the Froude number. This study offers valuable insights for enhancing the safety of transportation infrastructure in the Jiuzhai-Mianyang Expressway and mountainous regions of southwestern China.