A constitutive model for the hydro-chemo-mechanical behaviour of chalk

The mechanical properties of soft, highly porous carbonate rocks are known to be significantly affected by water saturation: both stiffness and strength decrease for wetting in the short term and for chemical dissolution in the long term. Both processes mainly affect the bonds between the carbonate grains: immediately after inundation depositional bonds fall into suspension whereas diagenetic bonds dissolve more slowly. In this work a strain hardening hydro – chemo - mechanical coupled elasto-plastic constitutive model for soft carbonate rocks is presented. The concept of extended hardening rules is here enriched: weathering functions are determined by employing a micro to macro simple upscaling procedures. Chemical damage is introduced in the formulation by means of a scalar damage function and its temporal evolution is also described using a multiscale approach. A new term is added to the strain rate decomposition tensor in order to incorporate the dissolution induced chemical deformations developing once the soft rock is turned into a granular material. The reference material is chalk from Butser Hill in Hampshire. After calibration, the model is validated by performing finite element simulations of rigid footing experiments from literature.