On the methodology for considering scale effect of rock strength

Serhii Skipochka¹, Oleksandr Krukovskyi¹, Tatiana Palamarchuk¹, Liliia Prokhorets¹

¹Institute of Geotechnical Mechanics named by N. Poljakov of National Academy of Sciences of Ukraine, Dnipro, 49005, Ukraine

Min. miner. depos. 2020, 14(4):24-30

https://doi.org/10.33271/mining14.04.024

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      ABSTRACT

      Purpose is to improve a methodology for considering the influence of scale effect by transferring to the evaluation of rock strength immediately within the rock mass.

      Methods. The research involves methods of critical analysis, theoretical and experimental research methods in the laboratory and full-scale conditions. In particular, there are statements of probabilistic and statistic theory, standard strength tests of rock specimens, laboratory studies of coal cutting resistance, and evaluation of rock strength by impact pulsing within the rock mass.

      Findings. It has been determined that rock strength depends considerably on the sizes of specimens being tested. That is stipulated by high porosity and fissility of the material. Measurement error decreases along with the increasing specimen size. There is the ultimate size, beginning from which its following increase does not results in considerable changes in the strength indices. For instance, in terms of Western Donbas coals, such an ultimate size is represented by a cube with the faces of not less than 100 mm. It has been shown that despite its high density, considerable scale effect is observed in hard rock as well; the effect is stipulated by the available zones with anomalously high porosity and coarse grains. It has been specified that minimum sizes of specimen faces for hard rock should be not less than 150-200 mm. Tests of such specimens are rather labour-intensive; they are often beyond the capacities of standard equipment. It has been concluded that structural anomalies of rocks require application of the methods which help evaluate their strength immediately within the rock mass; impact pulsing is one of those methods.

      Originality.Minimum sizes of hard rock specimens and rock formations, making it possible to exclude the influence of scale effect of strength, have been identified. Correlation dependences, connecting the informative parameter of the impact pulse method with the strength of different rock lithotypes, have been obtained.

      Practical implications. Methodologies for both considering scale effect of strength during laboratory studies and evaluating rock strength within the rock mass have been improved.

      Keywords: rock, strength, cutting resistance, scale effect, laboratory measurements, mine control

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