Determination of rational technological schemes for the completion of open-pits taking into account land reclamation

The analysis of objects of landscape disturbances under opencast mining is carried out. The arrangements for reclamation of residual mines and earth’s surface relief formation at the opencasts of the Pokrovskyi mining and processing enterprise are determined. The basic approaches for final extraction of opencasts in order to mining method are investigated. Reclamation processes during final open-pit mining are justified, taking into account the development of mineral reserves at the ends of the open-pit.


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policies in the mining area.At the same time, the trend analysis method in this study can quickly extract problem areas after dump regreening and is applicable in most dumps [12].
Conditions of the planning of open-pit mining objects have been identified, making it possible to reduce the need in the allotted land area during mineral extraction.The research results have allowed proposing a methodological approach to determine economic expediency of the increase in the technogenic land reclamation level under conditions of open-pit mining, being the reserves to expand the technogenic land areas returned to the economic use [13][14][15].
In the surface mining of mineral deposits, land resources suitable for agricultural purposes are inappropriately spent in large volumes [16].When mining deep open pits, overburden rocks are mainly transported to the surface.The optimal solution for reducing the area of disturbed lands is the placement of overburden rocks in internal dumps in the open pit.This is especially suitable when mining a mineral deposit with several open pits where at least one of them is depleted.Therefore, it is important to assess the feasibility of building an internal dump, based on the stability parameters of its slopes and the safe distance for placing mining equipment within its boundaries.
This article [17] investigates a new approach for mine waste management called the multi-stage dumping sequence, suggesting the use of temporary waste dumps along the way to the final dump destination.Although this method requires material re-handling, which is considered a paradigm in mine industry, it certainly provides additional time to design and permit the final waste dump site and, if well planned, might even result in profit increases by reducing haulage distances in the first years of operation.
The methodical approach to the technological reengineering of the open pit and the improvement of the technological scheme for the development of a horizontal deposit under the condition of providing competitive cost for mining minerals are generalized in order to eliminate the inconsistency of the high capacity of technological complexes of mining operations [18][19].
For the restoration of disturbed environment, final extraction stage of open-pit field and reclamation of residual mines is the final one and the most important among all stages of surface mining operations, because of that a lot of surface disturbances occurred, accumulated and did not eliminated during all the previous stages and for now they should be eliminated during the last stage.All man-made disturbances can be systematized in two categories due to their impact on the environment: 1) landscape (mined-out area, dumping areas, land for industrial sites); 2) environmental (changing hydrogeologycal conditions, pollution of off-site areas, air and water reservoir, seismic disturbances).
Mineral outputs of manganese ore in Ordzhonikidze MPE (Table .1) indicate that the Olexandrivskyi open-pit will be a subject of mine closure in 2-3 years, the Zaporiz'kyi open-pit -after 10 years.Other open-pits are provided with ore reserves which are sufficient for their operation for 15-20 years or more.As the previous stage of preparation to reclamation, the operations of covering the space between opencasts of the Severny and the Shevchenkivskyi should be included in working projects of opencasts reclamation.Also at the Chkalovskyi №2 opencast creating of residual trenches of the main open-field should be put in reclamation working projects that allow increasing the area of reclamation.The protection of mining trenches from underflooding should be always carried out.
For a long time (20-25 years and over) production capacity of the Pokrovskyi MPE can support the Pokrovsky opencast, where carbonate ore is produced.For the maintenance of the productivity of this mining enterprise the development of stand-by condition reserves of the Zaporiz'kyi open-pit should be provided that requires developing of respective flowsheets.For the excavation of ore reserves the flowsheets of block's mining operations (by four blocks) are developed by this article's authors.The comparison of flowsheets is performed according to the volume of overburden operations.
The purpose of the article is an assessment of the current prospects for deposit exploitation of the Pokrovskyi MPE, a systematization of technological and organizational measures for reducing negative effects of mining complex on the territory of final exploration of manganese open-pits.

2.Methods
For a comparative technical and economic assessment, technological schemes were adopted, which provide for the use of ESh -15/90 stepping excavators instead of ESh -20/72, taking into account that the annual ore productivity of the Zaporiz'kyi open-pit is not standardized for PMPE.In particular, additional factors known from the theory and practice of open development of flat deposits are taken into account, which allow reducing the Kr factor, such as: 1) reduction of the width of dragline's cut; 2) reduction of the entire thickness of overburden rocks, which are worked out according to the complicated stripping method up to the limit height of 30-40 m.
Taking into account the specified changes, various technological schemes (I-IV and VI) can be recommended, the essence of which is shown in Figure 1a and 1b, which shows schemes I (II) and IV.These schemes differ, first of all, in the width of the cut that works the dragline, both in the initial value and in the calculated parameters and indicators.Features and differences of schemes III, IV and VII are presented in table 2.

3.Results and discussion
The main calculated technological parameters of each scheme under consideration is the resulting slope angle of the internal dump βrez.It is possible to adjust its value (decrease or increase) in two ways.The first way involves unloading the internal dump by re-excavating rocks in its upper part with an additional dragline (ESh-20/72 or ESh-6/45).At the same time, the angle βrez is determined by the formula: where Н0 -height of internal dump, m; Н3 -height of lower sub bench, m; h -height of ore, m; В -safe distance between the axis of movement of the dragline and the upper edge of the pre-dump, m; Ra.д -unloading radius of the additional dragline, which is installed in the upper part of the dump (Figure 1а), m.
Formula (1) can also be used for schemes IV and VI.For other schemes: where О is the distance between the axes of the dragline on the front slope (Figure 1а), m.
The above-mentioned approach to adjusting the βrez angle can be most effectively used in case of the need to re-excavate a part of the rocks under the condition of the receiving capacity of the upper layer of the dump.So, for scheme II, using an additional dragline of small linear parameters (for example, ESh-6/45) and re-excavating rocks with a volume of 189 m 3 /m of the length of the dump front of the works (Figure 1a), it is possible to reduce the βrez angle from 18-20 0 to 15-16 0 (scheme II).
The values of the βrez angle obtained for all the considered schemes (Table 2) not exceed the maximum permissible under the condition of stability.For the mining-geological and hydrological conditions of the of the Zaporiz'kyi open-pit, the limit values of the resulting slope angle of the internal dump are 20-21 0 with a factor of stability reserve η=1.1.
It should be noted that most often the described approach to adjusting the βrez angle leads to an increase in the amount of rock reexcavation.Therefore, it must be taken into account in each individual case.Recommended flowsheets are complicated dragline mining method of overburden with the height of 45 and 55 m and combined mining method (with the height up to 70 m), which includes transport mining method with the use of vehicles and complicated dragline mining method (Figure 1a and 1b).Also a combined mining method is developed, where the height of overburden of 55 m is developed by the dragline mining method and the height of 15 m due to transport mining method with the use of the excavator of loading shovel type and trucks.Proposed technological solutions allow reducing the reexcavation factor of overburden significantly as well as adjust the value of the resulting slope angle of internal dump to ensure its sustainability.
The final extraction and reclamation of the Zaporiz'kyi open-pit will be carried out soon.The tasks of the implementation of productive equipment and opencast mining method of overburden on the top bench as well as activities for the protection of overburden trenches from the underflooding are urgent for making decisions nowadays.Cost effectiveness of applying of recommended flowsheet of final extraction of the Zaporiz'kyi open-pit is substantiated.

Area of disturbed lands
The object which removes land area

Technological and organizational measures
Land allotment The processes of reclamation and covering of the end face of opencast under its final extraction cause considerable problems.Developing of opencast end face areas by dragline mining method is complicated because of that the length of stripping front exceeds the length of dumping front.It is connected with the creation of transport inclines or cross-over for the load and transport connection of extracting bench with the surface.Full or partial extracting of ore bed in the end face can be performed by additional mining and transport equipment according to transport or dragline flowsheets when overburden are transported outside of the opencast field.
Measures for land protection in manganese opencasts, which are being on the final stage of the extraction of deposits reservoir are shown in the Table 3.
The transfer from parallel advance of frontal operations under the final extraction of the previous opencast to fan-shaped one for the preparation of the next opencast (area) is provided by the technology of deposit reclamation and covering of mined-out area.It help to reduce the volume and site of minedout area and create the favorable conditions for its covering by the overburden from the following opencasts or their areas.

Conclusions
The stage of final extraction of open-pit area and reclamation of residual mines is concluding.A lot of disturbances are accumulated during all previous stages but should be eliminated during the last stage.
At the open-pits of the Pokrovskyi MPE the measures of the preparation of favorable conditions for the reclamation of residual mines and forming of indicated surface relief should be carried out.The internal dump of wheel-bucket complex is advisable to reclaim without carrying a layer of clay loams and humus.
For the extraction of ore reserves at the Zaporiz'kyi open-pit the technological scheme of mining method by the blocks should be introduced.Complicated stripping method is recommended for the capacity of overburden of 45 and 55 m.Combined mining method that includes mining system with the use of vehicles and complicated stripping method are recommended for the capacity of overburden up to 70 m.These decisions enable to reduce the reexcavation factor of overburden significantly as well as provide the stability of internal dump.Under final open pit extraction considerable difficulties will be caused by processes of reclamation and covering an end faces of open pit by overburden.

Table 2
Initial and calculated parameters and indicators of technological schemes that are compared