Modélisation multi-échelle du comportement différé des géomatériaux anisotropes – MELANI

This proposal is devoted to experimental investigation and numerical modelling of time dependent behaviour of geomaterials, in particular anisotropic rocks materials. The initial anisotropy of such materials is generally related to the presence of initial defeats such as bedding planes, fractures and cracks. During ulterior loading, the initial defeats can evolve and new micro-cracks can develop and grow, leading to microstructure change of materials. These microstructure evolutions can modify the anisotropic nature and significantly affect macroscopic properties of materials. It is then necessary to develop suitable modelling in order to account for microstructure evolution and interaction between initial and induced anisotropies. Moreover, the microstructure evolution is also origin of time dependent behaviour of material. In classical investigations, the time dependent behaviour is generally described by viscoplasticity theory; this approach provides an efficient mathematical tool to deal with time dependent deformation, but can not properly take into account physical origins involved. Indeed, in a number of cases, the viscosity is not the unique origin of time dependent deformation; other important phenomena can exist, such as sub-critical propagation of microcracks with stress corrosion, dissolution of inter-granular contact areas by pressure solution process. In the present project, it is proposed to deal with two complementary features: laboratory testing and in situ investigation in order to identify different phenomena which are origin of time dependent deformation; and develop a multi-scale approach for numerical modelling by including the identified mechanisms. Two representative rocks, sedimentary rock and poly-crystal rock, will be selected in this work. The present proposal will deal with three jointed features: experimental characterization of different mechanisms responsible to time dependent behaviour and determination of overall creep deformation in laboratory and in situ; development of multi-scale and multi-physics approach for numerical modelling; numerical implementation, validation and application. These features will be organized in 8 tasks, which are described in detail in the research program: ? Task 1: experimental characterisation of phenomena; ? Task 2: experimental investigation of chemomechanical coupling; ? Task 3: characterization of overall time dependent deformation; ? Task 4: in situ experimental in situ; ? Task 5: formulation of a basic constitutive model for instantaneous mechanical behaviour of rocks ? Task 6: extension of the basic model to time-dependent behaviour; ? Task 7: consideration of chemomechanical coupling; ? Task 8: numerical implementation and validation.