Uncovering the coupled fluid and solid dynamics driving highly-localized rupture in geomaterials (UNLOC)

Earthquakes, glacier collapses, land and rock slides; many of the various kinds of unpredictable natural disasters are preceded by a rupture running through rock mass or sediments. In UNLOC, we will study the physical similarities at the origin of these different kinds of catastrophic failure and describe the key processes governing the propagation of rupture in geomaterials. The complexity of geomaterials emerges from the solid microstructure, which can either be continuous, fractured, or granular, and fluids that fill the pore space. Like in a sandcastle, the amount and pressure of fluids control the mechanical behaviour and strength of the material. During failure, this coupling becomes particularly intricate as the rapidly deforming solid interplays with the dynamic fluid flow within the pores. In UNLOC, we will get unique experimental insights on the mechanical conditions governing rupture, first in an idealized porous material and then in natural rock and sand whose failure will be imaged at high resolution by a powerful X-ray scanner at the European Synchrotron Radiation Facility. In synergy with the experimental campaigns, we will develop computational and theoretical models to simulate and explain the propagation of rupture at the origin of catastrophic events in geomaterials. In a context of global climate change, there is an increasing societal need to assess the risks posed by the rapid transformation of alpine and polar environments. UNLOC will make the developed models and numerical tools versatile and freely accessible to future research projects. Throughout the project, we will collaborate with an artist to exhibit the main findings and challenges of the project to a broad audience.

The propagation of highly-localized ruptures precedes various kinds of catastrophic failures in geomaterials. Examples include landslides, rockfalls, glacier surges and earthquakes. Quantitative predictions of these processes remain elusive and challenging because material failure stems from highly-localized shear bands that focus deformation down to the pore scale. In UNLOC, we will perform ground-breaking basic research to simulate and image the highly-localized micro-mechanical processes that cause the rapid failure of geomaterials. The UNLOC team will develop and release a multi-scale theoretical and numerical framework capable of bridging the gap between these two relevant length scales. The development and validation of the developed models will be conducted hand-in-hand with two experimental campaigns. The first one will image the localized deformation of dry and wet natural rocks and sands using synchrotron X-ray microtomography, and the second one will image and quantify dynamic fluid flow in a rapidly opening cavity. UNLOC will bring new insights into the universal micro-mechanical mechanisms that cause failure in geomaterials and improve knowledge on the role of pore fluid in those processes. Our overarching goal is to establish a firm theoretical and numerical framework that can be readily adapted to the diversity of systems prone to develop localized failures.