Designs, technologies and temperature conditions of frozen structures in placer mines in the North

Many gold mines in Russia are located in the Far East, including the permafrost zone. Efficient mining of deep placers in such conditions is only possible with the underground method. It is proposed to ensure roof support in mined-out areas in placer mines using frozen rock pillars of an original design capable to provide an increased load-bearing capacity. Such pillars are constructed using an improved technology, with metal pipes placed layer by layer in the body of a pillar at certain intervals. Efficiency of the proposed method for pillar freezing is evaluated using the developed mathematical model. The model uses the two-dimensional nonlinear equation of thermal conduction (Stefan problem), which enables prediction of temperature condition in the frozen pillar and enclosing permafrost formation in placer mines. The new computer program allows selecting geometry of a frozen rock pillar, construction dates, physicotechnical properties of rocks, as well as the number and arrangement of metal pipes to inject cool air for more intense freezing of the pillar. Computer modeling is undertaken to compare the rate of construction of a frozen rock pillar using the conventional and proposed methods. The modeling results confirm that freezing of a pillar of a proposed design takes much shorter time as against the conventional approach due to the forced circulation of cool air in pipes. Dynamics of cooling and subsequent freezing of a frozen rock pillar constructed in placer mines in the conditions of higher rate of ventilation is determined. The features of heat exchange between the frozen rock pillar and surrounding permafrost formation in placer mines are revealed. The feasibility of appreciable acceleration of freezing in the proposed-design frozen rock pillar and the resultant development of strength is proved. Such design frozen rock pillars possess high strength, ensure reliable support of mined-out areas and improve operational safety in placer mines in the permafrost zone.

Kaimonov M. V., Kiselev V. V. Designs, technologies and temperature conditions of frozen structures in placer mines in the North. MIAB. Mining Inf. Anal. Bull. 2020;(8):118129. [In Russ]. DOI: 10.25018/0236-1493-2020-8-0-118-129.

M.V. Kaimonov¹, Cand. Sci. (Eng.), Senior Researcher,
V.V. Kiselev¹, Cand. Sci. (Eng.), Senior Researcher,
¹ Chersky Mining Institute of the North, Siberian Branch, Russian Academy of Sciences, 677018, Yakutsk, Republic of Sakha (Yakutia), Russia.

M.V. Kaimonov, e-mail: gtf@igds.ysn.ru.

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