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Coal
Published in Peter M. Schwarz, Energy Economics, 2023
Underground mining is still the predominant form of mining in developing countries, as well as in developed countries where coal seams are deep. One technique is room-and-pillar that may be followed by a final stage of retreat mining. Room and pillar mining builds rooms into the coal mine, leaving pillars to support the roof. To maximize profit, the rooms and especially the pillars must be of optimum size. Pillars are left-behind resources, so larger pillars leave behind more resources. However, smaller pillars increase the chance of a mine collapse. Retreat mining removes the coal pillars to get the remaining coal, increasing the danger that the mine roof could collapse.
Pillar design issues in coal mines
Published in Xia-Ting Feng, Rock Mechanics and Engineering, 2017
As mentioned before, since the classic approaches do not consider the abutment loads, they are not suitable for mines where retreat mining is going to be done. In retreat mining, the creation of a mined-out gob area generates abutment loads. Abutment loads affect the pillars adjacent to the pillar line and a load more than the one estimated by tributary area theory applies on pillar. Pillar design without the abutment loads leads to failure of pillars during retreat mining. So, proper pillar design is the key to prevent the pillar failure and reduce accidents related to retreat mining. In the US, the LaModel and the Analysis of Retreat Mining Pillar Stability (ARMPS) programs are used successfully for designing safe retreat mining (Tulu et al., 2010). LaModel is a PC-based program for calculating the stresses and displacements in coal mines or other thin seam or vein type deposits (Heasley & Barton, 1999; Heasley, 2009). It is primarily designed to be utilized by mining engineers for investigating and optimizing pillar dimensions and layouts in relation to overburden, abutment and multiple seam stresses. The program was developed based on displacement-discontinuity variation of the boundary element method. The ARMPS computer program was developed by National Institute for Occupational Safety and Health (NIOSH) to aid the design of pillar recovery operations (Mark & Chase, 1997). ARMPS is an empirical method in which the statistical analysis is used to derive design guidelines that separate the “successful” case histories (those where the entire panel was mined without pillar failure) from those that are “unsuccessful”. The goal is to minimize the risk of the most hazardous types of pillar failures (collapses and bumps). Like classic pillar design methodology, ARMPS consists of three basic steps: (1) estimate the applied loads, including development and abutment loads; (2) estimate the load bearing capacity of the coal pillars; and (3) compare the load to the capacity, and employ engineering criteria to determine whether the design is adequate.
Mining method selection for extracting moderately deep ore body using analytical hierarchy process at mindola sub- vertical shaft, Zambia
Published in Cogent Engineering, 2022
Víctor Mutambo, Samuel Kangwa, Marsheal Fisonga
Based on the assessed criteria, RMR ranked high with 23.83%, followed by thickness with 15.31 % and powder factor with 15.11%. When the criteria are evaluated with the alternatives, the mining method with the highest score of 18% was Vertical Crater Retreat (VCR), followed by Sublevel open stoping with 16.62%. Vertical retreat mining, is an open stopping, bottom-up mining method that involves vertically drilling large-diameter holes into the ore-body from the top, and then blasting horizontal slices of the ore-body into an undercut using spherical charges, which has a length to diameter ratio of 6:1 or 4: 1. VCR is also referred to as the modern version of sublevel open stopping, which has done away with sublevels. The ore-body characteristics for the Mindola mine given in (Table 2) are favourable and in conformity with this mining method’s sphere of application.