Influence of ore draw mode on freezing losses during underground mining of permafrost deposits

In the underground mining of mineral deposits in the permafrost zone, the freezing of broken ore in the working excavation is one of the key factors that have a significant negative impact on its efficiency. During the ore drawing from the block in conditions of negative temperatures, the determining factor influencing the freezing of the ore is the change in the moisture content of the ore mass, even within insignificant limits, and the time it is in a stationary state. The article presents the results of an experimental study of the influence of the modes of area ore drawing on the loss of ore mass from freezing under conditions of negative temperatures in the working excavation. Physical modeling of the area ore drawing was carried out taking into account the mining and geological, mining technical and thermomechanical conditions of the underground mining of one of the ore deposits of Yakutia. The experiments were carried out with uniformly sequential, layered and chaotic ore drawing modes and various degrees of ore mass moisture content in a cryochamber at the air temperature of minus 5°С, using a specially made test bench. It was found that at the natural negative temperature of mine air and the temperature of the broken ore of minus 5°C, an increase in its moisture content by 1% leads to an increase in freezing losses in layered mode by 22%, and with the uniformly sequential and chaotic ore drawing modes by 29–30%. The established dependencies are valid only for specific thermal and humidity conditions of the experiment, however, they allow a qualitative assessment of the effect of the ore drawing mode on the loss of broken ore from freezing in underground conditions at negative temperatures of the mine air and adjacent strata.