Longwall mining

Abstract: Underground Mining Methods presents the latest principles and techniques in use today. Reflecting the international and diverse nature of the industry, a series of mining case studies is presented covering the commodity range from iron ore to diamonds extracted by operations located in all corners of the world. Industry experts have contributed 77 chapters. This book is certain to become a standard for every practicing mining engineer and student alike. Sections include: General Mine Design Considerations, Room-and-Pillar Mining of Hard Rock/Soft Rock, Longwall Mining of Hard Rock, Shrinkage Stoping, Sublevel Stoping, Cut-and-Fill Mining, Sublevel Caving, Panel Caving, Foundations for Design, and Underground Mining Looks to the Future.

Abstract: The fractured zones caused by mining were studied in the overburden of the Torezko-Snezhnyanskaya area, Ukraine, through the change in natural gas emission from these zones during longwall coal excavation. Zones of interconnected fractures and separate horizontal fractures were studied with vertical wells drilled from the ground surface down to active underground workings. The maximum heights of the zone of interconnected fractures and separate horizontal fractures may reach 19–41 and 53–92 times the thickness of the coal seam respectively. It was found that the ratio between the maximum height of the zone of interconnected fractures and the thickness of the extracted coal seam increases with the increasing number of rock layer interfaces and decreases with the increasing stiffness of immediate roof. It is shown that the growth of the zone of interconnected fractures occurred during 17–39 days at an average rate of 0.94–1.97 m day−1 and it was accompanied by increasing methane emission from overburden. Observation shows that the formation of separate horizontal fractures began only 11–49.5 days after the height of the zone of interconnected fractures reached its maximum value. Formation of separate horizontal fractures in overburden over the longwall excavation occurred as a stepped process from lower to upper sandstone–sandy shale layer interfaces in the direction of the ground surface.

Abstract: The impact of mining subsidence on the environment can occasionally be very catastrophic, destroying property and even leading to the loss of life. Usually, however, such subsidence gives rise to varying degrees of structural damage that can range from slight to very severe. Different types of mineral deposits have been mined in different ways and this determines the nature of the associated subsidence. Some mining methods result in contemporaneous subsidence whereas, with others, subsidence may occur long after the mine workings have been abandoned. In the latter instance, it is more or less impossible to predict the effects or timing of subsidence. A number of different mineral deposits have been chosen to illustrate the different types of associated subsidence that result and the problems that arise. The examples provided are gold mining in the Johannesburg area; bord and pillar mining of coal in the Witbank Coalfield, South Africa; longwall mining of coal in the Ruhr district; mining of chalk and limestone in Suffolk and the West Midlands, respectively; and solution mining of salt in Cheshire. These mineral deposits have often been worked for more than 100 years and, therefore, a major problem results from abandoned mines, especially those at shallow depth, the presence of which is unrecorded. Abandoned mines at shallow depth can represent a serious problem in areas that are being developed or redeveloped. Abstraction of natural brine has given rise to subsidence with its own particular problems and cannot be predicted. Although such abstraction is now inconsequential in Cheshire, dereliction associated with past subsidence still remains.