ACME 2011 Proceedings of the 19 UK National Conference of the ...

horizontal confining pressure is maintained at a constant value whilst the vertical pressure is
incrementally increased at the rate indicated. The properties that describe the behaviour of the material are
provided in Owen et al. 2007, where the parameters required are readily identified from standard triaxial
and tension tests. In addition to the usual elastic properties, the essential parameters are the tensile
strength, compressive strength, fracture energy release rate and the standard Mohr-Coulomb data. An
additional parameter is the frictional sliding coefficient on newly created discrete cracks. The material
parameters employed correspond to Lac du Bonnet granite (Lee et al. 1993) and the weak sedimentary
rock Cardova cream limestone (Haimson et al. 1993).
Figure 1. Borehole breakout example:
Geometry and mesh.
Figure 2: Comparison of experimental and
numerically predicted failure patterns for Granite
(upper)and Limestone (lower)
Figure 2 illustrates the fracture patterns developed for the two materials where it is seen that
fundamentally different mechanisms are involved. For the granite specimen, Figure 2(a), failure takes
place by the development of sub-vertical fractures at the regions indicated and very good agreement is
evident between the experimental observations (Lee et al. 1993) and the numerical predictions. In Figure
2(b) similar comparison is made for the Cardova cream limestone, for which failure takes place by the
development of fracture shear bands. In the computational model these manifest themselves as distinct
crack bands formed by en-echelon systems of tensile fractures. Again, there is a strong correspondence
between the experimental failure mode (Haimson et al. 1993) and the numerical simulation. It is
important to note that the computational model has been able to reproduce these two fundamentally
different failure mechanisms by only changing the relevant material parameters.
Fluid flow within fracturing rock masses
Throughout the geomechanics community there is considerable interest in modelling groundwater flow
through fracturing rock masses. Application areas include slope stability problems and hydraulic
fracturing in the oil recovery industry. The essential features of such problems are the flow of water both
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