Institute of Integrated Mineral Development — IPKON, Russian Academy of Sciences, Moscow, Russia:

V. N. Zakharov, Director, Professor, Doctor of Engineering Sciences
O. N. Malinnikova, Head of laboratory, Doctor of Engineering Sciences, olga_malinnikova@mail.ru
A. P. Averin, Senior Researcher, Candidate of Engineering Sciences

Currently Russia produces 30 % of coal using the underground method. The available mining equipment enables excavation rate of 15–20 m/day and the production face advance at a rate of 12–15 m/day in longwalling. Introduction of heavier duty machines considerably increases energy transmitted to coal–rock mass. Rock mass in production face area has no time to relax and release excess energy in this case; as a result, rock mass becomes geodynamically unstable and experiences high-energy vibrations and oscillatory processes in exposed walls. This study is aimed to estimate influence of mining operations on energy of vibration and oscillatory processes in coal–rock mass areas subjected to mining impact. The estimates are based on the experimental research and mathematical modeling. The modeling used the ANSYS software with the finite element method. Explosion load on a coal bed was simulated as a violent displacement of the bottom of a blasthole drilled from a development drive on the lower bed in the model of two close-spaced coal beds, in conformity with the actual blasting parameters. The research shows that in coal–rock mass under mining, vibrational energy mainly crowds in a coal bed: in the stress concentration zone and in the influence zone of small-amplitude dislocations. An explosion, as the highest intensity impact, generates inflow of additional energy in the form of vibrations, comparable with the energy of elastic deformation of a coal bed. The resultant displacements (1–2 mm) nearby the blasting point imply an incipient failure of coal on an intermolecular level, with breaking of long bonds at edges and with generation of active radicals (including methyl groups), typical of coal and gas outbursts, which may induce generation of extra methane. Therethrough, a source of initiation and growth of high-energy dynamic event e arises in the face area of a coal bed, which can increase content of methane in mine air.
The study has been supported by the Russian Science Foundation, Project No. 16-17-00029.

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