Research of strength and features of deformations of rocks in uranium deposits

Abstract

The subject of the research was physical and mechanical properties of rocks from uranium deposits in Ukraine. The purpose of the work was to study the strength characteristics and features of deformation of rocks of uranium deposits beyond their strength limit to ensure the stability of mine workings at great depths. Research methods were experimental with using stationary laboratory equipment and special recording equipment. The studies were carried out within and beyond the strength limits. The rock specimens were made of material taken from a uranium mine. The complex of the studies included determination of general physical properties of rocks (density, specific gravity, porosity, humidity and adhesion coefficient); basic strength parameters (compressive and tensile resistance depending on humidity and layering, angle of internal friction, elastic modulus, Poisson's ratio, modulus of decrease and residual strength) and deformation characteristics. Calculations of the scale strength factor were made. The results were analyzed. It is shown that the rocks of uranium deposits in Ukraine are considered strong and very strong, according to the Protodyakonov scale. However, structural and textural features lead to the occurrence of a scale effect of strength of rocks. The complex structure of uranium deposits, the steep angle of dip of the rocks, their lamination, as well as the significant size of the mine workings further reduce the strength of the massif. It is also shown that when calculating stability of mine workings and choosing parameters for their support, the strength of rocks in the massif should be reduced by half from the value obtained by standard laboratory tests. The characteristics of rock samples within and beyond their strength limit indicate that they have almost no plastic properties. The ratio of the modulus of decrease to the static elastic modulus for all studied types of rocks of uranium deposits is greater than one. This indicates the tendency of rocks to accumulate potential energy and cause brittle failure of the massif beyond its compressive strength. That is, at great depths, the main problems in mine workings associated with rock deformation processes will manifest themselves in the form of rock bumps, collapses or other dynamic phenomena. This does not exclude the possibility of deformation or destruction of rock support due to static loads. Keywords: uranium deposit, rock, laboratory research, extreme stress, physical properties, strength, elasticity, scale factor.