Scale Effects in Geomechanics
B. Z. Amusin
Retired, New York, USA
Keywords: Rock mass classifications, scale effects, creep, mechanical characteristics of rock mass, fractal analysis
Abstract
The limitations of traditional methods of rock mass classification are reviewed. A modification is proposed for the Hoek-Brown failure criterion, with the compression strength of rocks presented in an explicit form. An approach to the compression strength assessment is taken on the ground of generalized results obtained by Kim in experiments with model block structures made of equivalent materials. An approach to determination of scale effects on strength, deformation modulus, creep and internal friction angle is described. The constant of creep is introduced, and the correlation dependences are obtained to find the creep constant in four types of rocks. It is found that the ratio of displacement at the boundary of a mine opening to displacements in the plastic strain zone can be approximated by a function of the internal friction angle only. This concept is used to calculate internal friction angles in rocks from the analysis of field measurements. The author puts forward two hypotheses and makes an attempt to substantiate them. Hypothesis A supposes that a scale effect in similar structure rock mass depends on the compression strength, and weaker scale effects are typical of hard and brittle rocks as against softer and plastic rocks. Hypothesis B supposes that time of stress and strain relaxation increases in a larger rock mass volume while the strain rate decreases.
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