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The methods we use to describe the anisotropic strength of closely jointed rock masses are highly subjective
and experiential. Consequently, there is a need to construct an ‘equivalent material’ that honours the
strength of the intact rock and joint fabric within the rock bridges that may occur along a candidate failure
surface in a closely jointed rock mass. We then need to be able to use this model to simulate the brittle
fracture that can and does propagate across the joint fabric within the rock bridges as the rock mass
deforms. It has been found that the Bonded Particle Method utilised by the Itasca PFC numerical modelling
codes may be able to provide such a material model. Known as the Synthetic Rock Mass (SRM) model, the
model represents the intact rock in the rock bridges with an assemblage of bonded particles and the joints by
a sliding joint model that allows associated particles to slide through, rather than over, one another and so
represent joints that slide and open in the normal way. In 3-D block caving simulations SRM rock bridge
fracture has been found to be widespread. From a rock slope stability point of view the model has the
potential to provide a means of developing a strength envelope that does not rely on either Mohr Coulomb or
Hoek-Brown criteria. Similarly, the inverse of providing Hoek-Brown parameters and calibrating the Hoek-
Brown strength envelope should also be possible. A rock mass characterisation program with numerical and
empirical comparisons involving SRM test samples calibrated with intact rock and joint data coming from
different mine sites has therefore been developed to test the concept in conjunction with studies to utilise the
model in PFC and continuum/discontinuum codes for slope stability analysis purposes.
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