Micro and meso scale investigation of the mechanical instability within rock faults

Short term visitor's project

To clarify the mechanism of instability in rock fault geo-bodies, we will analyze the distribution and evolution of the micro- and meso-structures in the rock faults at the initiation and development of the failure. The instability will be characterized by the so-called “second order work criterion”, which is renowned for detecting all instabilities by divergence in rate-independent materials

Using a Discrete Element Method (DEM), a slope model with a band of rock faults will be built according to a real Chinese slope that already failed after the excavation of its foot. The slide process will be simulated and monitored. When the slope undergoes a global instability, two aspects in the rock faults zone should be analyzed:

• on the micro-scale, the spatial and temporal evolution of local second order work (c-) on contacts, as the microscopic contributions to the global second order work;
• and on the meso-scale, the developing force-chains, the column-like grain (or contact) clusters carrying a major part of the loading of the material.

By analyzing the distribution of contacts with negatively valued local second order work and buckling force-chains, how the local instability appears, propagates and eventually leads to a global instability will be elucidated. 

A shear test for a thin layer of idealized rock faults will be conducted also from DEM simulations. Considering different loading conditions, macro and micro quantities related to material instability will be tracked during loading history. The second order work criterion will be computed to report the state of global stability, as the vanishing second order work characterizes the occurrence of a material instability. For loading conditions able to lead to global instability, c- and force-chain buckling will be monitored around some characteristic moments.

A special effort will be made to investigate the underlying micro- and meso-mechanism of the instability in rock faults.