The influence of flooding on underground coal mines

[摘要] English: The purpose of the study is to investigate the influence of flooding on underground coal mines. Two case studies were investigated the shallow underground Klibarchan coal mine and the deep underground Usutu mine. Kilbarchan colliery is located 10 km south of Newcastle in KwaZulu/Natal. It comprises two underground sections, called Roy Point and Kilbarchan. Usutu colliery is situated just 8 km outside the town of Ermelo in Mpumalanga, close to Camden power station on the N2 road to Piet Retief. The geology of both studies lies within the Karoo Group, Ecca subgroup in the Vryheid formation. Higher precipitation at Usutu and Kilbarchan occurs in the summer months, while Kilbarchan has a higher annual rainfall of 864 mm/a compared to Usutu's 705 mm/a. The water levels at both mines yielded interesting findings. Usutu mine is compartmentalized with walls in the underground. These walls are so strong that they function as 'low pressure seals resulting in compartmentalized underground, withstanding the huge pressures created by the recharged groundwater. This causes water levels to differ in the underground. Water levels at Kilbarchan mine vary in depth, but when plotted in metres above mean sea level (mamsl) they plot in a straight line. Regional recharge at Usutu was calculated as 5.7 % and 11.3 % at Kilbarchan. Recharge is influenced by what type of mining activity was practised in that specific area. It was concluded that recharge on opencast is between 15 to 20%, the stooped area between 10-15% and in an underground shallow mine it could be as high as 10%. Mining activity ceased in 1992 at Kilbarchan. Pumping is a common practice at flooded underground mines, because the mine needs to be filled with water on an ongoing basis. This prevents sulphate generation and the water quality from deteriorating. Pumping at Usutu is well managed and flushing started to occur in the underground with the electric conductivity improving over time. Pumping at Kilbarchan is poorly managed and over pumped. The electric conductivity over time, is not improving indicating that oxygen infiltrates the system when too much pumping occurs. Bord-and-pillar mining followed by stooping has been the main mining method. At Usutu mining activity ceased in the late 1980 and then the mine was flooded. It is finally there is concluded that an underground should be flooded as quickly as possible and then managed well. Shallow underground mines have a higher potential of contamination, because of a shorter residence time. The depth of mining, topography, mining methods, water levels, exposure to oxygen, rainfall, recharge, residence time and pumping have an influence on the effects of a flooded coal mine.

[发布机构] University of the Free State