Longwall mining activities alter the exsisting ground stress field, this changed stress field is known as induced stress. Extraction of coal by longwall mining induces a redistribution of stresses causing the rocks near the mining excavation to accomodate a redistributed load.
Effective and efficient longwall mining is dictated by the magnitude and orientation of the major and dominant stress present at the mine site. In Australia, the dominant stress component is horizontal stress. The figure opposite shows the stress concentration occurring around the extracted area. Thus it is important to mine the panel as near as possible to parallel with the high horizontal stress direction. The level of stress concentration increases as the angle between the direction of mining and the direction of the major horizontal stress increases. In general the loads occuring on the retreating facing are not uniform. The magnitude of the stress varies along the length of the face and is maximum at the centre of the face.
Topics that will be covered in this module are: