Analysis of the behavior of the Veveyse bridge under impact of massive rockslides ::a practical case study

On February 2, 2024, a landslide of several hundred cubic meters caused several massive rocks (50 to 100 m3) to fall down the slope of Vevey valley region in Switzerland. The rockslide hit and damaged part of the structure of the A9 Lausanne-Saint-Maurice national road/bridge before settling at the bottom of the slope near the bridge foundation. Luckily, the rockslide did not cause any casualties, nor did it affect any homes. Noting that the structure “Pont de Veveyse” consisting of 2 parallel and identical composite steel and prestressed concrete bridges that was put into service in 1969 ensures the passage of approximately 61000 vehicles/ day. In the bridge region, the geological conditions are very complicated and are characterized by an extended sliding zone that experiences slippage of a few cm per year. Since in this region, erosion and thus, slope as well as rockslides occur naturally and often, the following study was performed to determine the behavior of the bridge under different rockslide impacts. Following the accident, field investigations were conducted to gather information and identify the trajectory of the rockslides and bridge damage. Then, based on the principle of linear impulse and momentum as well as the conservation of linear impulse and momentum, the velocity of rockslides as well as the average impulse forces were calculated. The obtained results were used in the numerical simulations performed using the non-linear software Abaqus to investigate the bridge behavior and responses caused by the impact of the massive rockslide. The effects of impact load, its direction and location on the behavior of the bridge were examined. The obtained results showed that the simulated damage mechanisms agree with field observations. Moreover, bridge stability is affected by the rockslide impacts. The obtained results can be considered a mean to assess the stability of the bridge and perform as guidelines for authorities to mitigate future hazard rockslides impact strategies for the A9 bridge.