Modelling the water injection induced fault slip and its application to in-situ stress estimation

Fault reactivation due to water injection is assessed within the scope of nuclear waste disposal design. A model using the distinct element method is applied to reproduce the fault reactivation during an experiment carried out at the Mont Terri Underground Research Laboratory in Switzerland. A conceptual model is first presented to understand the hydro-mechanical coupling behavior between water pressure and rock joint movement. The model simulations show that the dominant factors on fault slip are shear stress and frictional resistance. Moreover, modeling shows that fault reversible opening in the normal direction occurs first at a lower pressure, whereas shear displacement as a result of shear slip is produced once a sufficiently high pressure is reached. We demonstrate that a coupled numerical analysis of the rock displacement trend and fluid pressure measured at the injection point allow an in-situ estimation of the principal stresses.