Substantiating the rational parameters for a complicated non-transport system when mining low-thickness fireclay deposits

The paper examines a complicated non-transport system for mining a gently sloping fireclay deposit using ESH-10/70 dragline excavators. The research purpose is to substantiate the technological scheme of stripping operations and determine their parameters to reduce the strip-mining costs. Theoretical research is performed using the following methods: methods of scientific analysis of theoretical research, as well as practices of project and production organizations; mining-geometric calculations; variant method for comparing and selecting a mining system. As a result, the dependence of the excavator block mining velocity on the entry way width has been determined, which makes it possible to study the relationship between mining and stripping equipment in time. The change in the re-excavation coefficient depending on the width of the dragline excavator entry way has been studied and its rational value has been determined. The practical value of the research results is in the substantiation of an effective system for mining a gently sloping fireclay deposit.


Introduction
Mining and export of mineral resources are today the driving force in the development of the economies of many countries around the world [1][2][3].In modern Ukraine, various types of mineral deposits are also mined.The vast majority of minerals are mined by open-pit mining method.Open-pit mining is considered to be the most efficient and cost-effective method due to its high level of productivity and lower initial capital operating costs [4][5][6].Along with large iron-ore deposits, Ukraine has a powerful mining of fireclays, which are widely used for the production of refractory products used in construction, metallurgy, mechanical engineering and other industries [7,8].
Ukraine owns huge fireclay reserves, deposits of which have been explored within the Donetsk folded structure, the Ukrainian Shield and the Dnipro-Donets depression.The main area of fireclay distribution is the Donetsk folded structure, where more than half of Ukraine's reserves are concentrated [9].One of the leading enterprises producing high-quality fireclay is VESCO PJSC, which mines the Andriyivsky field.
Open-pit mining of fireclays in the Andriyivsky field assumes a high stripping ratio, which is due to the low mineral deposit thickness of 1.6 m, and the average thickness value of sediments is 28 m.
The high thickness of the overburden rocks determines the combined systems of the field mining.For example, in the Zakhidnyi Quarry No.1, the front bench is mined with hydraulic excavators using a transport mining system, and the next benchwith a dragline using a complicated non-transport mining system.The main share of costs for stripping are related to the mining of the front bench, which is due to the costs for transporting the rock mass and the costs of renting hydraulic excavators [10].
Therefore, the issue of improving the quarry mining system and determining its parameters to reduce the cost for stripping operations is relevant.
Experience in using a non-transport system shows that with one piece of equipment, the efficiency of the technological scheme varies significantly depending on the location of the dragline excavators and directly on the mining system parameters.In this case, determining the mining system rational parameters is a difficult task [11].To do this, many factors should be taken into account, namely: mining-technical conditions of the field, parameters and performance of excavators, as well as the interrelation of the mining system elements.
One of the methods for selecting rational non-transport mining system parameters is the graphicanalytical method.It consists in multiple selection of the dimensions for the technological scheme elements, and the criterion for efficiency is obtaining a minimum re-excavation coefficient.This method is complex due to multiple design of the mining system with different parameters, but using computer modeling it is significantly simplified.Therefore, the research uses a graphic-analytical method to determine the mining system rational parameters.

Determining a link between the mining rate of the stoping bench and overburden bench
One of the most important factors when choosing a mining system is the rate of the deposit stripping, that is, ensuring the front of mining operations for the mining of mineral resources.To do this, it is necessary to coordinate the operation of stripping and mining equipment [12].
The velocity of mining overburden benches in a complicated system directly depends on the dragline excavator performance and its face parameters.With a complicated non-transport mining system with upward and downward diggings using one dragline excavator, its performance drops by 15-20% unlike its operation with only downward digging [13].This is due, first of all, to an increase in the angle of the dragline rotation and a more complex digging process during the upper mining of the bench.It is possible to increase the dragline performance only with proper organization of the excavator operation.
The excavator face parameters have a direct impact on the volume of the block mined by the dragline [14].As a block expands, its mining time also increases.However, when considering the velocity of advance along the front of mining operations, the movement of the dragline to a new block should be taken into account.Therefore, it is necessary to consider the excavator face parameters in order to ensure a sufficient velocity of the stripping operations.
The main dragline excavator face parameters are the height and width of the entry way [15].The height of the bench in the case of the complicated mining system of the Zakhidnyi Quarry No.1 is determined by the geological structure of the field and the excavator parameters.Thus, the average height of the upper bench will be 8 m on loams, and the lower -20 m on sands.Therefore, this research examines the influence of the excavator entry way width on the advance velocity of the overburden and stoping benches.
To determine the influence of the entry way width on the velocity of mining the overburden bench, it is necessary to calculate its maximum and minimum values according to safety conditions.
When using a non-transport mining system, the dragline excavator is located at a safe distance В1 from the upper edge of the bench, which is ensured by the angle of stable structure of overburden rocks.With a complicated mining system, the safe distance from the upper edge is also taken into account [16,17].To determine the maximum entry way width of the dragline excavator, it is necessary to take into account the parameters of the upper bench and the transport berm.Thus, given the above, the maximum entry way width of the lower bench of a dragline excavator with a complicated mining system with upward and downward diggings is determined by the formula: here Rd.maxmaximum digging radius, m; Hup.b.height of the upper overburden bench, m; αslope angle of the upper overburden bench, deg.
Maximum entry way width of the upper bench is calculated by the formula: After performing calculations, it possible to determine the excavator entry way maximum width for the lower and upper benches, respectively: Аmax.l = 59 m, Аmax.up = 52 m.
Based on the safety conditions, the minimum entry way width for the lower bench of a dragline excavator is determined by the formula: here Rbexcavator body rotation radius, m.
For the calculation, the minimum entry way width of the upper bench is taken to be 7 m less than the minimum entry way width of the lower bench Аmіn.up = 9.5 m.
The total time for mining one excavator block consists of the time for direct mining of the block tmining and the time for moving the excavator to a new block tmov.Thus, the time for mining one block is determined from the expression: The time it takes for excavators to move to a new working block is influenced by many factors, such as the dragline movement velocity, the driver's qualifications, and the block length.Also important is the time for planning the site on the bench, the time for transferring, installing and connecting to the power transmission line network.
The time it takes to move the excavator to a new working block tmov is calculated by the expression: The block length on the upper bench is limited only by the excavator parameters, and the block length during the downward digging is limited by the height of the bench and the physical-mechanical properties of the rocks.Based on the above, the block length, when mining the lower bench, is calculated using the expression: here αз -the slope angle of the dragline face, αз=45 о ; rbradius of the dragline excavator body, m; a safe distance from the stable bench upper edge to the excavator body, m.
The block length is 44.5 m.The bulldozer performs the planning of the track for moving the excavator, then the planning time is determined by the expression: here Splthe planned site area, m 2 ; hlaythickness of the planned rock layer, m, hlay = 0.3 m; Qbul.per bulldozer performance, m 3 /hour.The Zakhidnyi Quarry No.1 uses Cat D8R bulldozers.Their performance according to technical specifications is Qbul.per= 300 m 3 /hour.
The duration of moving the dragline excavator to a new block is 0.96 hours.With a complicated mining system with upward and downward digging, the dragline excavator mines the upper and lower bench from one installation place.Therefore, when calculating the duration of mining a block, the parameters of the upper and lower blocks are taken into account.From here, the duration of mining the blocks is calculated by the formula: here Qе.hourhourly performance of the dragline excavator.
The ESH-10/70 theoretical performance is 680m 3 /hour.However, when an excavator operates with upward digging, the cycle duration increases due to a more complicated digging process and an increase in the excavator rotation angle.Therefore, with a complicated mining system, the hourly dragline performance is 350-450 m 3 /hour, with the lowest value taken for calculation.
Knowing the maximum and minimum values of the ESH-10/70 entry way width according to safety conditions, the total time for mining the blocks can be calculated.Based on the calculation results, the dependence of the change in the time of mining the excavator blocks on the entry way width of the lower bench tbl = f(Аl) (Fig. 1) can be determined, as it is the lower bench that influences the entry way width of the mining excavator.From the data shown in the graph (Fig. 1), the time for mining the blocks with a dragline excavator increases with an increase in the entry way width, which is caused by an increase in block volumes.
Having determined the time for mining the blocks, it is possible to determine the velocity of mining the overburden benches along the front of mining operations using the formula: Knowing the parameters of the mining excavator and the required annual performance for mining of minerals Аminer=100 thousand m 3 , it is possible to determine the advance velocity of the stoping bench mining along the front of mining operations, given that the entry way width of the stoping bench with a complicated mining system will be equal to the entry way width on the lower bench.For this purpose, the necessary hourly demand for mining of minerals is determined, taking into account the number of working days per year at the enterprise is nwork= 241 days.
By determining the velocity of mining the overburden and stoping benches at different values of the excavator entry way width, it is possible to find the dependence of the advance velocity on the entry way width for the overburden and stoping benches, and also construct a dependency graph voverb = f(А) and vstop = f(А) (Fig. 2).

Figure 2. Dependence of the velocity of mining the benches with a variable entry way width
From the data shown in graph (2) it is clear that the velocity of mining the overburden benches is greater than the velocity of mining the stoping bench at different values of the entry way width.This makes it possible to assert that the ESH-10/70 excavator provides the stripping ratio of the required volume of minerals over time at different entry way width values.

Determining the rational parameters for a complicated non-transport mining system
For the conditions of the Zakhidnyi Quarry No.1, explore the possibility of using a complicated non-transport mining system with one ESH-10/70 excavator operating on the overburden bench.The dragline will work with both upward and downward diggings with direct placement of overburden into the internal dump.
The possibility of using this technological scheme for stripping operations will be tested using a graphic-analytical method by constructing a mining system with the specified bench height parameters, provided that the slope angles are stable.The entry way width is assumed to be minimal according to safety conditions.When constructing a scheme, the volume of the internal dump should be greater than the volume of overburden rocks, taking into account the loosening coefficient.
The flowsheet is presented in Figure 3.As it can be seen from the data presented in Figure 3, the volume of overburden that can be placed into the internal dump is less than in the overburden bench entry ways: Therefore, the use of this technological scheme is impossible.Next, consider a complicated nontransport mining system using an excavator in stripping operations and in a dump.This technological scheme consists of additional re-excavation of rock with a dump excavator located in the pre-dump area for additional movement of rock.
The mining system parameters depend on the mining-geological conditions of the field.Thus, the height of the upper overburden bench is equal to Нup=8 m, the height of the lower overburden bench is Нl=20 m.Therefore, it is necessary to determine the rational entry way width of the dragline excavator.To do this, using the graphic-analytical method, the volume of rocks to be re-excavated and the re-excavation coefficient [18] can be determined by the formula: To determine the volume of mining operations, it is possible to construct a flowsheet for a complicated mining system with various parameters of the entry way width (Fig. 4).The obtained data are presented in Table 1.To determine the rational entry way, the dependency graph of the re-excavation coefficient is plotted when the width changes (Fig. 5).As can be seen from the dependency graph, the minimum re-excavation coefficient is achieved with a minimum entry way width, however, the value of the re-excavation coefficient increases insignificantly by 6% when the entry way width increases to the maximum value.Therefore, the rational value of the entry way width is A=30 m, since with this value of the entry way width, the greatest use of the excavator is achieved in time, and the maximum visibility of the face for the excavator operator is provided.

Economic assessment of the proposed mining system
The criterion for assessing the effectiveness of the proposed mining system is the specific cost for strip-mining of 1 m 3 [19,20,21,22].Therefore, we will calculate all cost items for this stripping site, and based on the obtained data, construct a histogram for calculating unit costs for mining the Zakhidnyi Quarry No.1 site (Fig. 6).As can be seen from the data shown in Figure 6, the main share of costs with the existing combined mining system is spent on fuel and electricity, and with the proposed complicated non-transport mining system, the main costs are only for electricity.This is due to the refusal to use dump trucks and diesel excavators.By eliminating equipment rental costs and reducing fuel costs, the cost of 1 m 3 of stripping operations is reduced by 17.51 UAH.Consequently, the proposed mining system can reduce the cost of 1 m 3 of stripping operations and gain additional profit.

Conclusions
The paper examines the improvement of conducting stripping operations in the conditions of the Zakhidnyi Quarry No.1 of the Andriyivsky fireclay field, mined by VESCO PJSC.The research performed makes it possible to determine the maximum and minimum possible values of the entry way width for a dragline excavator under safety conditions and during upward and downward diggings.It has been revealed that with a complicated non-transport mining system, the maximum value of the entry way width is Аmax.= 59 m, and the minimum is Аmax.= 16.5 m.
The dependence of the velocity of mining the overburden and stoping benches on the entry way width has been determined for a complicated non-transport mining system, which allows us to state that with the required mining of minerals in the amount of 100 thousand m 3 /year, the velocity of mining the overburden benches is greater than the velocity of mining the stoping bench, given the different values of the entry way width.
After determining the re-excavation coefficient for different values of the excavator entry way width, it has been revealed that the re-excavation coefficient increases by 6% when the entry way width increases.Taking this into account, the rational ESH-10/70 entry way width is 30 m, since with this value of the entry way width, the greatest use of the excavator is achieved in time, and the maximum visibility of the face for the excavator operator is provided.
Economic efficiency from the implementation of a complicated non-transport mining system using ESH-10/70 draglines in the Zakhidnyi Quarry No.1 will reduce the cost of stripping operations compared to a combined mining system by 37.1%, which means additional profit in the amount of 30.81 million UAH per year.
here lbl -length of the block mined by the dragline excavator, m; tsw.cthe time spent on switching the cable network, hour; tpltime spent on planning the track for moving the dragline, hour; υе -the dragline excavator movement velocity, m/hour.Theoretical velocity of ESH-10/70 movement is υе=200 m/hour.

Figure 3 .
Figure 3. Complicated mining system using a single stripping excavator

8 Figure 6 .
Figure 6.Structure of unit costs per 1 m 3 of stripping operations

Table 1 .
Parameters for a complicated non-transport mining system with different entry way width