Effect of Methane Pore Pressure on the Geomechanical State of Massif in the Vicinity of the In-seam Working


N.V. Cherdantsev, Dr. Sci. (Eng.), Chief Research Associate, nvch2014@yandex.ru FITs UUKh SO RAN, Kemerovo, Russia

Annotation:

The model of the geomechanical state of the coal-rock massif containing in-seam working driven on the gas-bearing bed is presented. The model is built based on the basic provisions of the mechanics of the deformed rigid body and linear mechanics of fracture. It assumes that the massif is in the conditions of the deformed state and is loaded with the gravitational stress field. It is considered that the characteristics of the strength of the coal seam are less than the characteristics of the strength of the rocks of the hosting massif, but higher than the strength characteristics on their contact. The conditions for the occurence of the inelastic deformations are the adopted criteria for strength of Coulomb-Mor and Mor-Kuznetsov. In this connection, the problem of the stress-strain state of the coal-rock massif is the elastoplastic problem.
Gas pore pressure changes deep into the bed in accordance with the hyperbolic tangent function. At the edge of the bed it is equal to atmospheric pressure, and far from the edge — hydrostatic.
The model assumes that when formulating the boundary conditions at the contact of bed with the lateral rocks, the microcracks with methane pore pressure are oriented vertically. In this connection, in the boundary conditions the horizontal component of the hydrostatic pressure decreases to the value of the methane pore pressure.
By replacing the plastic part of the bed with the normal and tangential stresses acting on the bed contact, the elastoplastic problem is reduced to the boundary-value problem of the theory of elasticity.
To assess the growth of microcracks under the influence of methane pressure the criterion is used, which is obtained within the frame of linear mechanics of fracture.
In the course of the simulation experiment carried out within the frame of the developed model, the graphs of the dependence of the main stresses, methane pore pressure and the indicators of the microcracks growth from the coordinate counted along the contact of the bed with the lateral rocks were plotted.
It is established that taking into account the methane pore pressure in the model insignificantly effects the parameters of the bearing pressure, but gives fundamentally new results with regard to crack growth in comparison with the model, in which the effect of methane pressure is not taken into account.

References:

1. Petukhov I.M., Linkov A.M. Mechanics of rock bumps and emissions. Moscow: Nedra, 1983. 280 p. (In Russ.).
2. Malyshev Yu.N., Trubetskoy K.N., Ayruni A.T. Fundamentally applied methods for solving the problem of coal bed methane. Moscow: IAGN, 2000. 519 p. (In Russ.).
3. Plaksin M.S., Ryabtsev A.A. Specificss of the development of dynamic gas manifestations in the course of conducting development working. Naukoemkie tekhnologii razrabotki i ispolzovaniya mineralnykh resursov = Science-intensive Technologies for the Development and Use of Mineral Resources. 2017. № 3. pp. 67–73. (In Russ.).
4. Shadrin A.V. Effect of simplification of the methods of the current forecast of coal beds outburst hazard on the reliability of the forecast. Vestnik Nauchnogo tsentra po bezopasnosti rabot v ugolnoy promyshlennosti = Vestnik of the Scientific Center on Safety of Work in the Coal Industry. 2017. № 2. pp. 31–33. (In Russ.).
5. Kozyreva E.N. Possibilities to improve the efficiency of gas emissions control at the working area. Vestnik Nauchnogo tsentra po bezopasnosti rabot v ugolnoy promyshlennosti = Vestnik of the Scientific Center on Safety of Work in the Coal Industry. 2017. № 3. pp. 30–35. (In Russ.).
6. Kozyreva E.N., Shinkevich M.V., Smirnov S.R., Isambetov V.F. Need in application of in-seam gas drainage on the specified gas content of the bed (for example, face № 449 of Chertinskaya-Koksovaya mine). Vestnik Nauchnogo tsentra po bezopasnosti rabot v ugolnoy promyshlennosti = Vestnik of the Scientific Center on Safety of Work in the Coal Industry. 2018. № 1. pp. 14–19. (In Russ.).
7. Shadrin A.V. Static and dynamic outburst hazard of coal seams. Bezopasnost truda v promyshlennosti = Occupational Safety in Industry. 2018. № 4. pp. 42–48. (In Russ.).
8. Guo H., Yuan L. An integrated approach to study of strata behaviour and gas flow dynamics and its application. International Journal of Coal Science & Technology. 2015. Vol. 2. Iss. 1. pp. 12–21.
9. Liu X., Yang S. Three-dimensional numerical simulation of methane drainage by high-level drill holes in a lower protective coal seam with a «U» type face. International Journal of Coal Science & Technology. 2014. № 1 (4). pp. 434–440.
10. Charehdash G., Barzegar M. Numerical models currently being developed for use in mining industry. Mine planning and equipment selection. Proceedings of the 22nd MPES Conference. Drezden: Springer, 2013. pp. 481–490.
11. Shatter R.J. Models of guasistatic and dynamic fluiddriven fracturing in jointed rocrs. 4th Conf. San-Antonio. 1987. pp. 505–518.
12. Fisenko G.L. Limiting conditions of rocks around the workings. Moscow: Nedra, 1976. 272 p. (In Russ.).
13. Cherdantsev N.V., Cherdantsev S.V. Analysis of the state of the coal-rock massif containing in-seam working and geological fracture. Izvestiya RAN. Mekhanika tverdogo tela = Izvestiya of RAN. Mechanics of Rigid Bodies. 2018. № 2. pp. 110–121. (In Russ.).
14. Cherdantsev N.V. Zones of rock discontinuity in the area of conjugation of two workings of square cross-section. Vestnik KuzGTU = Vestnik of KuzGTU. 2003. № 5 (36). pp. 19–21. (In Russ.).

DOI: 10.24000/0409-2961-2018-10-7-13
Year: 2018
Issue num: October
Keywords : boundary element method coal-rock massif in-seam working extremely stressed zones methane pore pressure strength characteristics
Authors:
  • Cherdantsev N.V.
    Cherdantsev N.V.
    Dr. Sci. (Eng.), Chief Research Associate, nvch2014@yandex.ru, Federal Research Centre of Coal and Coal Chemistry of SO RAN, Kemerovo, Russian Federation