Urban explosions, experiments and expertise – URBEX

The URBEX project aims at developing a validated, breakthrough, fast-running, meshless model for the propagation of blast waves in urban configurations, accounting for all urban effects: multiple reflections, diffractions, channeling in urban canyons and urban canopy bypassing.

The project intends to fill the gap identified between empirical operational or normative approaches (circular danger zones) and the use of 3D numerical codes requiring specific expertise and significant computing resources. Its applications concern global security and industrial security, as well as more generally the protection of people and goods.

The URB(EX)3 model will be able to compute a complex overpressure wave shape at any point in the zone of interest. Consequences on people and infrastructures will be computed using both regulatory overpressure thresholds and probabilistic consequence models from the literature.

The model will be embedded in an existing user-friendly platform, DEMOCRITE, developed during the eponymous ANR project and already tested by several organizations.

Model inversion will also be addressed for two applications:
1. Definition of a protection perimeter / a vehicle exclusion zone around a building or a user-defined zone for a given threat level;
2. Forensic analysis of the observed damage to estimate the likely equivalent explosive mass.

This model will be supported by series of analytical, high-quality, small-scale experiments in order to:
- Guide the fitting of model parameters, when necessary,
- Investigate specific phenomena, for instance blast channeling in city streets,
- Help quantifying model uncertainties and safety margins,
- Test the model on more global configurations,
- Prepare for further extensions (terrain effects, height-of-burst explosions…).

The only assumptions are:
- The explosion takes place at ground level, assuming hemispherical high-explosive shape,
- Free-field functions for blast parameters as a function of reduced distance: P(Z), I+(Z) , etc. are supposed to be known for the explosive under study,
- The urban configuration is given (for instance in the shapefile format) by a set of buildings, each of them described by its polygonal footprint and its height (this is the standard for the IGN BD TOPO® v3 database, and corresponds also to the CityGML level of detail 1 description),
- The terrain is flat.

However, some of these limiting assumptions (height of burst explosion, actual vs. simplified building façades, terrain slope, clearing effects…) will be questioned during the project through dedicated experiments and/or numerical simulations.

Finally, the partners have collected letters of support from several organizations, which will be part of the project's advisory board: IRCGN, LCPP, EURENCO, IRSN and CETID. The objective is to ensure that the project meets the actual needs of various potential users.