ISSN 1062-7391, Journal of Mining Science, 2017, Vol. 53, No. 5, pp. 801–810. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © V.V. Dyrdin, V.N. Oparin, A.A. Fofanov, V.G. Smirnov, T.L. Kim, 2017, published in Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh
Iskopaemykh, 2017, No. 5, pp. 3–14.
_________________________________ GEOMECHANICS _______________________________
Possible Effect of Main Roof Settlement on Outburst Hazard
in Case of Gas Hydrate Dissociation during Coal Mining
V. V. D y r d i n
, V. N. Oparin
, A. A. Fofanov
, V. G. Smirnov
, and T. L. Kim
Gorbachev Kuzbass State Technical University, Kemerovo, 650000 Russia
Chinakal Institute of Mining, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630091 Russia
Received August 28, 2017
Abstract— The results of physical modeling of geomechanical processes in outer zones of coal beds with
the main roof caveable with difficulty. The scope of the modeling embraces the inlfuence seams on gas
release by gas temperature and pressure variation during stage-wise outlet of gas from a pressure bomb,
which simulates cyclical mechanical impact on a coal seam in the zones of a gas pocket. It is found that the
low-frequency (2.0–4.5 Hz) attenuating vibrations generated in the main roof can induce both secondary rock
mass disintegration as well as methane desorption and decomposition of gas hydrates (if present) accompanied
by an increases in gas pressure and in number of gas-dynamic events in outer zones of coal beds.
Keywords: Gas-dynamic events, settlement, disintegration zone, gas pocket, methane gas hydrates, outburst
hazard, low-frequency vibrations, temperature, pressure, modeling.
Investigation into physicochemical processes associated with underground coal mining is crucial
for technological improvement and working safety.
Coal is mainly composed of high-molecular compounds produced by condensation from elements of
dead vegetation. Its chemical structure includes cyclic hydrocarbon rings with a fringe of methyl groups
, as well as H
. Coal contains pores and factures (cleats) filled with free or bound water
and natural gas (85–95% methane and minor amounts of nitrogen, carbon dioxide, hydrogen sulfide,
argon, and other gases, no more than 10–12% in total).
Coalseam methane can exist in a gaseous form, free or adsorbed on coal particles, or as crystalline
solids (hydrates). Methane hydrate consists of hydrophobic gas molecules trapped inside cages of
hydrogen-bonded frozen water molecules . Methane may also occur as intercalation compounds
that form by reversible reactions as gas ions are inserted between oppositely charged carbon layers.
The existence of natural methane hydrates in coal was first predicted and discovered by Makogon
. Later on we studied physicochemical effects related to the formation and decomposition of
methane hydrate in coal seams and its effect on coal and gas outbursts [3–5]. Natural gas hydrates
exist at depths under gas pressures of tens of bar and most often form cubic structures of types I and II
and less often a hexagonal structure of type H (Table 1). Coal contains only cubic (type I) methane
hydrates (Fig. 1), with their unit cell consisting of 46 water molecules making six large (T) and two
small (D) cages which can accommodate eight molecules of methane clathrate [6, 7]. Hydrates occur
as guests in polyhedral cages of the host lattice formed by hydrogen-bonded water molecules.
Table 1. Types of clathrate structures 
Type, space group
Unit cell size a, Å, cage density, ρ
Unit cell formula Guest molecules
Cubic (type I)
a = 12.0,
ρ = 0.796
Cubic (type II)
a = 17.1,
ρ = 0.812
, Ar, Kr
Hexagonal (type H)
a = 12.3,
ρ = 0.768