Stress-dependent mechanical properties and bounds of Poisson’s ratio for fractured rock masses investigated by a DFN-DEM technique

Abstract

Stress dependent mechanical properties and bounds of Poisson’s ratios for fractured rock masses are investigated using the Distinct Element Method (UDEC-BB), based on the geometry constructed by the Discrete Fracture Network approach (DFN-DEM technique). Results on a simple model with one fracture set show that mechanical properties are highly dependent on the magnitudes of stresses, and the Poisson’s ratio can be well above 0.5, the upper limit for the isotropic case. Numerical experiments with ten realistic DFN models suggest that elastic modulus of fractured rock masses increases substantially with the increase of stress magnitudes. A simple empirical equation relating the stress (s) and rock mass elastic modulus (Em) is proposed in the following form, 1/Em=1/Ei+1/(Sm×s), which fitted well with the calculated results. The calculated Poisson’s ratios generally decrease with the increase of stress magnitudes. The Poisson’s ratios obtained from realistic DFN models are also well above 0.5, which suggest that the common practice of assuming the Poisson’s ratio as 0.2 - 0.3 needs to be carefully re-evaluated for fractured rocks.