REC «Mekhanobr-Tekhnika» (St. Petersburg, Russia):

Vaisberg L. A., Scientific Advisor, Doctor of Engineering Sciences, Professor, Academician of the Russian Academy of Sciences

Petrozavodsk State University (Petrozavodsk, Russia):
Kameneva E. E., Associate Professor, Candidate of Engineering Sciences, Senior Researcher, elena.kameneva@mail.ru

Granite and gabbro-diabase samples are used to study the effects occurring in rocks with different texture, structure and porosity under compressive loads corresponding to approximately 10–90% of the expected compressive strength. The study is performed using X-ray micro-tomography (X-ray micro-CT). It has been established that, at loads corresponding to the specified range, plastic strains occur in the rocks, leading to irreversible changes in the volume of the samples after removal of the load. The change in volume is most pronounced in porous rocks (granite) and is less significantly manifested in dense rock (gabbro-diabase). At the initial loading stage (~10–40% of the expected compressive strength), the nature of the strain in the rocks studied shows no fundamental differences: the rock is compacted, which is accompanied by a decrease in the volume of the pore space and in the number of pores. A further increase in the load leads to decompaction of granite samples, which is due to an increase in the total porosity and pore size through combination of small differences into larger ones. In gabbro-diabase specimens, the compaction occurs throughout the entire range of loads studied. An increase in the volume of granite samples under increasing loads is accompanied not only by an increase in the volume of the pore space, but also by deformations of the mineral substance: the microcline, biotite and ore mineral buildups are compacted and the aggregates of plagioclase and quartz grains increase in volume.
The work was carried out with the support of the Russian Science Foundation (project No.17-79-30056).

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