In the design of underground excavations, elastic theory or elastic analogue methods are generally used to evaluate induced stresses and deformations. When a number of excavations are created, what could generally be considered a linear elastic material now gives a non linear deformational response to load which makes the use of any linear elastic method of analysis suspect.

If the material in which the excavations are created have joints and faults in the area of concern, the use of elastic analogue theory becomes even more suspect. The jointing systems allow the mechanisms of slip, rotation, and punching to occur. These mechanisms readily induce tensile stresses and strains within the individual blocks which in turn are now more susceptible to tensile failure with the consequent effects of load redistribution and further progressive failure.

The above features are examined using models of the Numbers 2 and 5 ore bodies located at Mount Isa Mines. Photoelastic material is used in constructing the models so that both stress distributions and deformations can be examined.

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