Numerical Modelling of Longwall Panels as an Aid to Mine layout Design

CIM Montreal 2003
David Reddish, Rod Stace,
Abstract D.J. Reddish, L.R. Stace and D.N. Whittles
School of Chemical, Environmental and Mining Engineering
University of Nottingham, United Kingdom

Abstract
Numerical modelling studies have been successfully used as an aid to planning the layout and support design both in the UK and in world-wide coal mines. The modelling of roadways, longwall panels and the interactions between longwall panels provides valuable information about the likely stress conditions and strata movements that will be encountered allowing more confidence in the design of roadway support requirements and methane drainage schemes. The availability of greater computer power has allowed the development of a modelling methodology for simulating the shear planes and stresses of the rock strata that develop around longwall panels.

The paper describes case studies of large scale regional modelling of two UK coal mines using the FLAC software code. The first case study describes modelling of two coal mine panels where methane drainage was required. The case study illustrates how the information provided by the model in relation to the magnitude, orientation and position of shear fractures and the areas of reduced and increased stress confinement was used to provide a means of planning and optimising methane drainage schemes for longwall panels. The development of a detailed geological model with realistic engineering properties and constitutive laws for the different lithological horizons utilising a dedicated rock mass classification scheme for coal measure strata is described. The modelling of the collapsed goaf or gob material is given special consideration.

The second case study describes modelling of a region of a UK coal mine 3.5 km wide by 0.9 km high in which one seam had been extracted by longwall and in which working had commenced in a second seam some 60m above the first extraction. The objective of the modelling was to predict the development of strata fractures and strains as the new longwall panels were extracted and, especially their relationship to an overlying sandstone aquifer. This case study also includes the investigation of the effect of mining on the behaviour of a fault that existed close to the start position of one of the panel. The potential effects of mining on the fault were modelled by parametric studies, adjusting properties for the fault and the relative position of extractions, which allowed the mine planner to position the panel layout accordingly.
Keywords: methane drainage, Numerical modelling, Longwall coal mining
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