Percolation model for dilatancy-induced permeability of the excavation damaged zone in rock salt

A new percolation model is presented that predicts the dilatancy-induced permeability increase in the excavation damaged zone (EDZ) of rocks salt. The micro-fracture geometry and network properties of the rock salt samples are determined by visualisation and evaluated by using statistical and stereological methods. The permeability at full connectivity is modelled using the cubic law with a semi-empirical estimation of the micro-fracture aperture. This model is coupled with a percolation model to incorporate the connectivity behaviour. The percolation threshold is related to the dilatancy boundary, which is defined as the starting point for the energy release that causes the grain boundaries to dislocate. The shift between the dilatancy boundary and the percolation threshold is further applied to complete the modelling approach. The model is calibrated and validated by the stress-permeability results of the triaxial measurements. The matches vary from satisfactory to excellent.

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