BULLDOZER DEVELOPMENT of the placers (EN: bulldozer mining; DE: Planierabbau; FR: exploitation au bulldozer; ES: explotacion por excavadora de empuje; RU: бульдозерная разработка) is the method for the conducting of the opencast mining works, for which the bulldozer is used as the major excavating machine. The bulldozer development is most effective for the depth of the embedment of the placer of up to 6 metres. At the greater depths, the bulldozer development is combined with the transportation of the rocks, and with the forming of the waste dumps, with the help of the hydraulic transport, of conveyors, of excavators, and so on.
Within the USSR, the bulldozers, as the major extracting machines, have started to be used for the first time for the development of the permafrost placers at the mines of the north-east of the USSR since the middle of the 40-ies. Since the end of the 60-ies, the bulldozers have got the distribution also for the development of the thawed placers (mainly at the extracting works). The increasing of the volumes of the bulldozer development was ensured, on the one side, by the growth of the power of the base tractors, and on the other side, by the technological advantages of the bulldozer development (the normal loading of the deflecting blade of the bulldozer for the layer of the loose rocks is 0.08-0.1 metres, the value of which corresponds to the natural daily thawing of the loose frozen rocks during the summer period). By the 1975, the volume of the bulldozer development within the total complex of the opencast works at the mines of the north-east of the USSR has increased to 89%.
The bulldozer development includes the conducting of the overburden stripping and extracting works. During the process of the bulldozer development, they perform the excavation of the rocks throughout the area of the stope: by the adjacent horizontal ploughings (the Figure # 1, a); by the grooves or trenches (the Figure # 1, b); in case of the insufficiently intensive thawing, or in case of the difficult to develop rocks, by the method with the sub-raking (the Figure # 1, v), and with the preliminary mechanical loosening (the Figure # 1, g). Sometimes, for the development of the liquified rocks, they use the paired work of the bulldozers (the Figure # 1, d).
The introduction of the bulldozer deflecting blade into the rocks, depending on their strength, is performed according to the straight layered (with the constant or variable thickness of the ploughing) and crested schemes. At the overburden stripping works, the bulldozers perform the complete complex of the processes, from the excavation of the rock within the stope, to the stacking of the rock into the waste dump, or perform only the excavation, while the transportation and the forming of the dumps are performed by other machines. As the major equipment at the overburden stripping works, they use the bulldozers most often during the development with separate excavation of the sands. They prepare the frozen rocks for excavation by the method of the natural thawing, less often by the drilling-blasting loosening. In the latter case, the performance of the bulldozer decreases by 25-30%.
In case of the bulldozer development, they distinguish the systems for the overburden stripping works, depending on the sequence of the movement of the stope (with the constant of blockwise movement), on the direction for the movement of the bulldozer, or on the type of the exit from the open pit mine. If the depth of the development does not exceed 4 metres, then they flatten the entire edge of the open pit mine, and are constructing the continuous exit from this open pit mine. In case of the greater depth, there is appropriate the construction of the individual exits, with the placement of them at the intervals of 40-60 metres along the length of the open pit mine. The continuous and individual exits may be situated outside the limits of the open pit mine, and completely or partly within it. In the latter two cases, at the end of the overburden stripping works, there remains the virgin pillar of the rocks of the overburden, which they excavate at the concluding stage. The selection of the type of the exit is determined by the width and depth of the open pit mine. They construct the individual exits from the open pit mine as direct and oblique, depending on the possibilities for the stacking of the dump for the overburden rocks according to the relief of the terrain. In case of the significant distances for the transportation of the rocks, the performance of the bulldozer development decreases. In these cases, there is advised the comprehensive work of the bulldozers and excavators, during which they distinguish the systems for the overburden stripping works, depending on the presence or absence of the accumulating trench within the open pit mine. The concluding operation during the overburden stripping works is the bulldozer stacking of the waste dumps. The stacking includes the throwing of the rock by the bulldozers from the top of the slope down the slope (the Figure # 2, a), or (more productive) the stacking of the waste dump using the parallel layers (the Figure # 2, b, v).
During the extracting works, they perform by the bulldozers, as a rule, the complete complex of operations, namely, from the excavation of the sands within the stope, to the delivery of these sands into the bunker of the washing installation; they use the additional technical means only for the transportation of the sands during their centralized washing. Depending on the direction of the movements of the bulldozers, they distinguish the systems for the extracting works: parallel, diagonal, fan-shaped, and with the angular movements. The general (major) direction of the movements is characteristic for each type of the bulldozer development (the Figure # 3).
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