Overburden stripping works
OVERBURDEN STRIPPING WORKS (EN: stripping overburden removal; DE: Abraumarbeiten; FR: travaux de deblayement, découverte; ES: desmonte; RU: вскрышные работы) is the removal of the rocks, which are covering the useful minerals, during the opencast development of the deposits. The overburden stripping works include the processes of the preparation of the rocky rocks for the excavation, the excavation-loading works, the transportation, and the forming of the dumps of the waste rocks. The overburden stripping works are conducted for the creation of the initial front for the extracting works during the construction of the open-pit mines, and during the period of the operation, for the preservation and advancement of this front. The overburden rocks, which are not containing the useful components, are removed into the external or internal dumps for the waste rocks. If the overburden rocks are suitable for the usage as the building mineral raw materials (for example, clays, sands, limestones, chalk, and so on), then they are subjected to the further processing (crushing, sorting, and so on).
The method of the preparation of the overburden rocks for the excavation includes: the protection of the soft rocks against the freezing, their thawing, the loosening of the strong rocks, which may be performed using the mechanical, drilling-blasting, hydraulic, physical (the electric currents of the high and low frequency, the thermal destruction), and chemical (dissolution, and so on) methods.
The excavation and loading of the loosened overburden rocks from the stope are performed, as a rule, using the excavators, digging-transporting (wheeled scrapers, bulldozers), and loading-transporting (single bucket loaders, and so on) machines.
The transportation of the rock is performed using the railway, automotive, and conveyor transport. Less often, there are used the skip hoists, hydraulic transport, and hanging ropeways. Sometimes, they use for these purposes the combined transport (for example, the mining mass is hauled from the stopes using the automotive dump trucks, and is moved further using the conveyor, railway, and hydraulic transport; through the ore passes, and along the ore chutes; through the hanging ropeways). The peculiarity of the movement of the overburden rocks is the variable position of the stopes and unloading places at the dumps for the waste rocks. The choice of the rational methods and comprehensive technological schemes for the conducting of the overburden stripping works depends mostly on the type, physical properties, and thickness of the overburden rocks, on the system for the development, on the requirements for the protection of the environment, and so on. According to the character of the works, and to the time of their performance, the overburden stripping works are sub-divided into mining-capital and current.
The mining-capital overburden stripping works are performed at various stages during the development of the deposit. There belong to these works the overburden stripping works, which are associated with the removal of the overburden rocks, and with the extraction of the useful minerals along the way, which are performed at the open-pit mine before its introduction into the operation at the starting level of the productive capacity. These works also include the construction of the initial mounds for the dumps for the waste rocks. After the start of the open-pit mine, till the reaching of the complete designed productive capacity by this open-pit mine, there is accounted for the mining-capital overburden stripping works the portion of the quantities of the waste rocks (which are determined using the technical-economical calculations) from the penetration of the permanent unsealing mine workings (the capital trenches and semi-trenches, tunnels, ore passes, and so on). During the reconstruction and expansion of the open-pit mine, there belong to the mining-capital overburden stripping works the penetration of the permanent unsealing mine workings, and the removal of the waste rocks, according to the quantity, which has been determined using the technical-economical calculations.
The current overburden stripping works are performed at the enterprise during the period of its operation. These works are performed for the clearing of the reserves of the useful minerals, which have been unsealed, for the conducting of the subsequent parts of the cutting trenches at the benches, which have been unsealed (for the increasing of the length of the front of the works), for the removal of the waste rocks, which are covering and containing the useful minerals, into the dumps for the waste rocks.
The expenditures per unit for the mining-capital overburden stripping works are usually more, than for the mining works during the period of the operation of the open-pit mine. The redemption of the capital expenditures is performed according to the so-called rate per tonne. If the capital mine workings are used only for the part of the open-pit mine field, then the rate per tonne is calculated using the division of the cost of these mine workings onto the reserves of the useful minerals, which are subject to the excavation with the help of these mine workings. The operational expenditures during the overburden stripping works are being redeemed using the addition of the current cost of the unit of the overburden, which is multiplied by the planned ("redemption") overburden stripping coefficient, to the current cost of the extraction of the unit of the useful minerals.
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