Effect of stress on mechanical and hydraulic rock mass properties -Application of DFN-DEM approach on the data from site investigation at Forsmark, Sweden

The purpose of this study is to demonstrate the effect of virgin rock stresses on the deformability and permeability of fractured rocks. Geological data were taken from the site investigation at Forsmark, Sweden, conducted by SKB. A set of numerical experiments was conducted to determine the equivalent mechanical properties (essentially, elastic moduli and Poisson’s ratio) and permeability using the DFN-DEM (Discrete Fracture Network - Distinct Element Method) approach. The results show that both mechanical properties and permeability are highly dependent on stress. Stress-induced anisotropy of mechanical properties was caused by hyperbolic nature of stiffness of the individual fractures. Stress induced anisotropy of permeability was observed due to different closure behavior of fractures, and in situ stresses influence the fluid pathways in the fractured rock mass. This study shows that proper characterization and consideration of in situ stress is important for the understanding of both mechanical and hydraulic behavior of fractured rocks.