Abstract
The verified Burgers' model for the pillars built of hard rocks corresponds qualitatively to their behaviour under the long term compressive load. During the experiments, both elastic immediate and after-effect (delayed) strains were observed. The occurrence of creep was proven for stress levels equal to or exceeding 5 MPa (about 40% of the ultimate strength of the fissured pillar samples). Approximated numerical rheological parameters:E 1,E 2,λ 1,λ 2 are, with a simplification, the parameters which can be applied in engineering computation since they are connected with strain characteristics of in situ pillar samples and not the rocks being only a component of broken-up rock mass. A thorough recognition of the effect of time on the behaviour of pillars during the mining of ore deposits is significant because of the possibility of their rational surveying and thus the decrease of exploitation losses. The results are the first to be obtained in in situ investigations and based on the classical creep test but on large-scale samples of pillars.
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