The majority of geotechnical analyses are deterministic, in that the inherent variability of the materials is not modeled directly, rather some "factor of safety" is applied to results computed using "average" properties. In the present study, the influence of randomly distributed shear strength is assessed via numerical experiments involving the compressive strength and stability of pillars typically used in underground construction and mining operations. The model involves combining random field theory with an elasto-plastic finite element algorithm in a Monte-Carlo framework. It is found that the "average" shear strength of the rock is not a good indicator of the overall strength of the pillar. The results of this study enable traditional approaches involving "factors of safety" to be re-interpreted in the context of reliability based design.
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