Prototyping to measure the interaction between debris flows and the existing building

This project is intended to initiate a process of reflection and to build a prototype to measure the interaction between debris flows and the existing building as accurately as possible: real damage occurring on a real building, after a real event. This project will result in a software application capable of assessing the damage of a real structure (made of reinforced concrete or wood, for example), taking into account its ultimate state of rupture, after a given torrential lava flow.

The steps to achieve this result will be as follows:

• Selection of several hazardous situations on the basis of historical documentation and/or existing natural hazard maps. Identification of the topography, stratigraphy, and driving action that led to the initiation of the flow of torrential lava.
• Construction of a 2D finite element model reproducing the topography, stratigraphy, and hydrogeological conditions associated with each situation. Introduction of a driving action, such as heavy rainfall, inducing a rise in the groundwater level, and identification of the mechanism of slope failure as a result of this action, and thus the potentially destructive volume of torrential lava.
• Propagation of the torrential lava along the slope, thanks to a second model taking into account the hydromechanical coupling and fine determination of the impact force on the threatened building - construction of a third model representing the real structure of the threatened building (reinforced concrete, reinforcements, wood, non-linear behaviour laws for the different materials), application of the impact force and prediction on the vulnerability of the building following this impact, according to the calculated displacement.
• Validation of the approach by comparing the damage estimated by the model to the damage caused by the debris flows in several real cases. The advantage and originality of this approach lies in its quantitative, physical character. Based on the representation of the various phenomena at play by a series of digital models, it goes beyond the current state of the art since it does not introduce any other approximation than that of the models that comprise it.

Landslides and debris flows are among the most common natural hazards on Swiss territory, but also among the most complicated to predict and model. According to a press release dated April 2018, the Swiss government has authorised the measures required to warn of landslides as part of the project 'Optimization of warning and alarm transmission systems'. According to experts [CH-2018 - Climate scenarios for Switzerland], precipitation will increase in frequency and intensity in the future and the danger of landslides and mudslides will increase. Most of the cantons have just completed their hazard maps and are currently examining these maps to assess potential hazards to the built environment.