Natural, pre-existing fractures 91Figure 7.2 (b) The Mountsorrel granodiorite, Leicestershire, UK, with complex fractur-
ing. Note the vertical fracturing and the presence of sub-vertical and transverse shear
fractures.
the mechanical weaknesses in the rock mass and they have a significant
effect on the rock mass deformability, strength, failure and permeability.
Moreover, failure often occurs along the pre-existing fractures.