By using the two-dimensional distinct element method and the code UDEC, this study numerically models the effect of fracture pattern on rock stresses. Three geological fracture pattern models are considered:
two parallel fractures,
multiple parallel fractures and
For each model, the mechanical properties of intact rocks, strength parameters of the fractures, boundary stress ratio K (K=s1/s2) and the angle a between fracture and the direction of maximum boundary stress are varied. By placing profiles or points in the models to monitor stress variation across fractures in the models, the quantitative relation between fracture pattern and the magnitude and orientation of stresses has been derived numerically. As a result, stresses in the vicinity of fractures are determined.
Knowledge of the in situ state of stress in the Earth's crust is very important for many problems in civil, mining and petroleum engineering and energy development, as well as in geology and geophysics (Amadei and Stephansson, 1997). It is also critical for the storage of toxic and radioactive waste in rock. Despite the importance of in situ stress and the development of a variety of methods to determine in situ stress in rock mass, rock stress has not been fully understood. A wide scatter of stress orientations and magnitudes is a proof of this fact and indicates that stress is influenced by several factors. The presence of geological fracture is one of the most important factors (Brady and Brown, 1985) and is also one reason for high horizontal stresses (Hudson and Harrison, 1997). Results of site measurements indicate that stresses reorient and their magnitudes vary in the vicinity of fractures. One example has been reported at the Underground Research laboratory (URL) located in Canadian Shield, where the shaft intersected two major thrust faults with splays.