Occurrence Of Outbursts Research Articles

Computation of gas pressure profiles relevant to outbursting in coal mines

AbstractHigh gas pressure gradients in coal seams play an important role in the occurrence of outbursts during underground coal mining. Excess stress resulting from body forces due to high pressure gradients contributes to the structural failure of coal. We present a one‐dimensional model of a dry, rigid coal seam with a moving mine face and determine gas pressures by solving the nonlinear equation for gas flow in a porous medium. An implicit finite difference scheme is used. Since the structure of coal has a dual porosity nature, we consider flow through both the macropores and the micropores. We investigate the effect of changes in mining velocity, idle mining periods and coal properties on the pressure profile in the coal seam. When the yield zone behind the moving mine face is taken into account, the greatest body force occurs on the least competent section of the coal seam.

Outbursts and geological structures in coal mines: A review

Novel aspects of stresses, gas and geological structure are integrated in a worldwide review of the problem of outbursts of coal and gas in coal mines. Based on a study of the literature and recent geological studies of outburst sites, geological structures have been identified as a prime factor in outburst occurrence. Thrusts, strike-slip faults and recumbent fold hinges are especially outburst prone. Such structures have been commonly referred to in the past as ‘tectonic disturbances’ or ‘soft coal’, and are the loci of highly fractured coal and gouge material. The nature of soft coal and gouge is not fully understood, but microscopic techniques are available for their study. In and close to geological structures anomalous stress and gas conditions apparently exist. At such sites mining-induced fracture systems, microseismic noise and abnormally high gas emissions have been recorded. Present knowledge of in situ stresses, gas regimes and geological structures at outburst sites is insufficient to enable an accurate mechanistic model to be formulated for outbursts. The most appealing mechanism advanced to date is called the ‘dynamic theory’, which emphasizes the role of stresses in the events leading to failure of the coal and control of the gas regime. A conceptual model based on this theory is proposed, which amalgamates all the factors known to influence outburst-prone coal extraction. The identification of geological structures, together with measurements of the various parameters of the gas and stress systems, may be the key to much more successful prognosis of outburst-prone zones than has been the case so far.

A hypothesis to explain the occurrence of outbursts in coal, based on a study of west wales outburst coal

A feature of outbursts in the Western part of the South Wales coalfield is the presence of a coal with unusual structural features in areas subject to outbursts. The effect of such a coal on the outburst process is discussed and a hypothesis presented to explain the mechanism of an outburst. This suggests that an outburst is a two-phase phenomenon, triggered by the dynamic failure of the outburst coal during the change from confined to unconfined stress conditions in the face of an advancing working excavation, and extended by the subsequent desorption of gas contained in the coal structure.