Comparative assessment of the operation quali- ty of shovel-truck systems at open-pit coal mines in the summer and transitional seasons

The operation quality of shovel-truck systems (STSs) at open-pit coal mines in the summer and transitional autumn-spring periods differs markedly. This is due to a decrease in the speed of haul trucks during the transitional season compared to the summer season. This leads to an increase in the travel time of trucks. Shovels and trucks must work longer to ensure the planned volumes of loading and transportation and the required number of hauls. Consequently, the duration of the working shift (or day) increases. This leads to deterioration in the STS performance in the autumnspring period. A quantitative assessment of changes in the STS operation quality will reveal the directions of its improvement.


Materials and methods
(coefficient of effective composition of the STS), (time to load a mining truck with a shovel), ℎ (duration of a truck haul) are the parameters to be optimized.
It was found in [12] that the speed of trucks in the transitional (autumn-spring) period decreases by 15-20% compared with the summer period. This leads to an increase in the travel time of trucks in the loaded ( ) and unloaded ( ) directions and in the haul time ( ℎ ). Shovels and trucks must operate longer to meet the scheduled volumes of loading and transportation and the required number of hauls. Consequently, the duration of the work shift (day) will increase, but should not exceed = 24 hours. To assess the influence of only the conditions of the autumn-spring period on the STS operation, all other indicators of this operation are left unchanged. The initial data for the calculations are given in Table 1. To obtain comparative characteristics, the basic values of the specific quality indicators according to the methodology given in [13] should be taken over the summer period.
From the optimal solutions for the summer (4) and autumn-spring (3) periods, it can be seen that the values of * do not coincide. This means that in the summer, the number of trucks servicing the same number of shovels should be more than in the autumn-spring pe-https://doi.org/10.1051/e3sconf /202131501016 E3S Web of Conferences 315, 01016 (2021) VI th International Innovative Mining Symposium riod. The reason for this is the long duration of a haul ( ℎ ) in the autumn-spring period due to the lower speed of movement, which means that the turnover of trucks is lower.
However, such a seasonal revision of the STS fleet structure is inappropriate. It makes sense to leave one value of the indicator . Obviously, this will be the smaller value * = 6,60, since for the autumn-spring period this is the maximum possible value. But the value of * for the summer period (6,653) can be reduced. A decrease in the value of * from 6,653 to 6,60 means that, in accordance with the margin for the limitation of the STS efficiency [11], its decrease will not be 1,529 (maximum), but 1,474. In proportion to this coefficient, the values of and ℎ will also change. The value of will be 3,627 minutes and ℎ will be 24,35 minutes.
The value of the functional criterion will be λ = 0,983, and the value of the generalized quality indicator will be k = 1,355.
The next difficulty lies in the fact that the actual values of the haul time in the autumnspring period are noticeably higher than the optimal value ℎ * = 23,88 minutes (5). To establish the relationship between the haul time in the summer and autumn-spring periods, we will carry out statistical processing of the corresponding data given in Table 1.
The communication equation has the following form: ℎ = 1,154 ℎ − 0,815 ± 0,097, where ℎ and ℎ are truck haul times in the summer and transition periods, respectively.
A change in the value of the indicator ℎ entails changes in the values of , λ and k in comparison with the optimal solution (5). We have from Table 2 that the reduction coefficient is 0,105, then = 3,627 minutes; λ = 0,877; k = 1,155.
The results of ℎ calculations for the given values of the haul duration ℎ are shown in Table 3. Minimum, maximum and recommended values are shown in bold.
To obtain complete data on the ratios of the indicators being optimized, the functional criterion and the generalized indicator of the STS operation quality for the given values of the haul time ( ℎ ), the corresponding calculations are carried out in a similar way. The results are also presented in Table 3. The actual values of the STS operation indicators for the summer period are indicated in the numerator, and for the autumn-spring period in the denominator.
A comparative analysis of the STS operation in the summer and autumn-spring periods shows (see Table 3) that the truck haul time ( ℎ ) in the autumn-spring period is on average 11% longer than in the summer period; the truck loading time ( ) does not change; the https://doi.org/10.1051/e3sconf /202131501016 E3S Web of Conferences 315, 01016 (2021) VI th International Innovative Mining Symposium functional criterion λ decreases by 11%, so does the generalized factor of the STS operation quality k -by 14,8%.
In [12,15] it is indicated that in the mining industry, the rational values of the match factor (in this case, the functional criterion λ) are less than 1,0 (optimal value), which corresponds to smaller fleets of mining trucks. At the same time, although the downtime of shovels is increasing, operating costs are significantly reduced, most of which falls on motor transport exactly.
All values λ ≥ 0,9 are acceptable (for the summer period of the STS operation it means: ℎ = 26,0 minutes; = 3,525 minutes; * = 0,895; * = 1,246). The value of the generalized STS operation quality indicator k = 1,246, in this case, exceeds the best value for the Company's mines k = 0,879 (Krasnobrodsky mine) by 29,5%; and 50,7% higher than in the whole Company (k = 0,614). In addition to the optimal and the above options, it is advisable to consider also the option with the maximum possible value of the haul time ℎ = 28,58 minutes (the worst option). Despite the fact that the value of the functional criterion in this case is only λ = 0,777, this is still 9,4% higher than that achieved at the Taldinsky mine, which is the best by this criterion (λ = 0,704), and the value of the generalized indicator (k = 1,062) is 17,2% higher than that achieved at the best Krasnobrodsky mine (k = 0,879).

Conclusion
Comparative analysis of the STS operation in the summer and autumn-spring periods shows that the duration of truck hauls in the autumn-spring period is on average 11,0% longer than in the summer period; truck loading time does not change; the functional criterion decreases by 11,0%, and the generalized quality factor of the STS operation decreases by 14,8%. The functional criterion values acceptable for the mining industry are 0,9 and higher. The value of the generalized indicator of the STS operation quality in this case exceeds the best one achieved by the Company at the optimal values of the truck haul duration by 29,5% and the average one in the Company by 50,7%. The use of even the worst option at the maximum possible value of the haul duration gives an increase in the functional criterion by 9,4%, and in the value of the generalized indicator of the STS operation quality -by 17,2%.
The work is executed within the limits of the complex scientific and technical program of a full innovative cycle "Development and introduction of a complex of technologies in areas of exploration and extraction of solid minerals, maintenance of industrial safety, bioremediation, creation of new products of deep processing from coal raw materials at consecutive decrease in ecological impact on environment and risks for population life" (CSTP "Clean coal -Green Kuzbass") on event 2.5 "Development and creation of an autonomous shuttle-type dump truck with carrying capacity of 220 tons (JU-PITER project)", with participation of T.F. Gorbachev Kuzbass State Technical University in terms of research, development and technological works.