|Room & Pillar Underground Mining|
Room and pillar mining is defined by the fact that portions of the coal seam being extracted are left in place to support the roof of the mine. Room and pillar mines are developed by using machinery to extract the coal seam in a grid like pattern through the development of a parallel series of extraction areas referred to as entries. The entries are connected together by extracting the coal perpendicular to the parallel entries in crosscuts. To support the coal extraction areas in the entries and crosscuts, roof support is installed by using machines to install long “bolts” into the roof of the mining area to consolidate and “tighten” the overlying rock strata. Referred to as “roof bolting”, this is the central point of a mine’s roof control plan that is developed by safety regulatory agencies and the operator to assure a maximum amount of safety by minimizing the possible occurrence of roof fractures and slips or roof falls. Figure A-2 provides an illustration of typical room and pillar mine in Appalachia.
Room & Pillar MiningCoal extracted from the entry and crosscut areas or “working faces” of the room and pillar mine is loaded onto special underground rubber tired haulage vehicles called shuttle cars. The shuttle cars move the coal from the working face to a centrally-located conveyor belt loading point where the coal is unloaded and transported to the surface for processing at the coal preparation plant. Some mines use shuttle cars to move the extracted coal to a loading point where it is transferred to narrow gauge railroad cars for movement to the surface. In slope and shaft mines there may also be a third transfer point where the coal from the working face is transferred again from the conveyor belt or rail car to an elevator-like haulage system where the coal is lifted vertically to the preparation plant. The initial development of a room and pillar mine, where entries and crosscuts are driven in the coal seam is referred to as primary extraction. Mines using primary extraction only can usually recover 40 to 60 percent of the coal in a given seam and reserve. Depending on the characteristics of the coal reserve, its overlying strata or roof and its underlying strata or floor, secondary production may be possible in room and pillar mines. In secondary production, some of the coal pillars that were established by the entries and crosscuts and were left in place for added roof control are removed. Extraction of the coal in the pillars, if possible at all, is governed by roof control and safety conditions as extraction of the pillars usually results in some level of roof collapse. Where it can be practiced secondary extraction is designed to remove the coal resource in the pillars in a calculated and designed fashion to allow for controlled roof collapse that will not endanger the safety of coal miners or compromise the overall geologic integrity of the entire mine. Where it is possible, secondary extraction can allow for recovery of 70 to 80 percent of the coal in a given coal seam.