There are various methods and techniques available for in-situ testing of the underground rock mass. Some of the strata mechanics instrumentation that are used can be categorised as follows : Stress Measuring Instruments, It is not possible to directly determine the stress characteristics of rock but it can be evaluated […]

Surface subsidence will gradually form when coal is extracted over a wide area from a moderate to great depth of cover. The factors which influence subsidence include the height if the caved area over the extraction and the degree of bed separation within the overlying strata. The amount of subsidence […]

The effective width of a large rectangular chain pillar can be calculated by using either of the following formulae: weff = (w1 x w2)0.5 OR weff = 4A/C Where: w1 = width of one side of the chain pillar (metres) w2 = width of the other side of the chain pillar (metres) A = Area […]

SINGLE SQUARE CHAIN DESIGN The load transferred from the adjacent goaf areas is dependent upon the depth of cover to satisfy subsidence compatibility. For sub-critical subsidence conditions the following expression is used to calculate the load supported by a pillar: for w/h < 2 tan f Where : w = […]

The diagram opposite shows a typical longwall panel with a single row of rectangular chain pillars. Chain pillars can be either square, rectangular or in some case diamond in shape. They can also be in a single or double row configuration. In Australia a single line of rectangular chain pillars is the […]

Lateral stress is thought to be generated by techtonic plate movements. The magnitude of lateral stress undergound is proportional to rock stiffness since the stress is induced by constant lateral dispalcement. Since the stress can not pass through the openinigs, it will concentrate around them. The optimal direction of drivage […]

In the diagram opposite, mining of a longwall panel results in the formation of front and side abutment pressures. The peak of the front abutment pressures can occur 1 to 3 metres ahead of the face and the extent of the front abutment pressures can be up to 50 metres […]

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 […]