Study of the Influence of Individual Factors on Drilling and Blasting Performance Indicators under the Conditions of the Eldorado Deposit
Abstract Generated abstract
This paper examines factors affecting drilling and blasting performance in exploratory workings at the Eldorado gold ore deposit, where hard schist and quartz vein rocks require blasting methods. Based on production experiments, the authors compare cut designs for workings driven across rock strike and assess the effect of stemming on blasthole utilization, advance per blast, and explosive consumption. The results indicate that selecting a lower or upper cut according to rock dip can improve excavation outlining and increase hole utilization, while stemming reduces explosive use per linear meter and improves advance efficiency. The study proposes adjusted cut selection and blasthole filling coefficients for local blasting practice.
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STUDY OF THE INFLUENCE OF INDIVIDUAL FACTORS ON DRILLING AND BLASTING PERFORMANCE INDICATORS UNDER THE CONDITIONS OF THE “ELDORADO” DEPOSIT
A. D. Gromov, V. G. Lukyanov
(Presented by the scientific seminar of the Department of Geodesy, Mining, and Construction)
The “Eldorado” gold-ore deposit is located in the northern part of the Yenisei Ridge. The deposit is represented by numerous quartz veins and veinlets situated in quartz-biotite and garnet-mica schists. According to the Unified Classification of Rocks by Drillability (ENB, 1969), the rock category is XIV–XVII; therefore, the workings are driven by drilling-and-blasting methods. They are driven both along the strike of the rocks (adits, drifts) and across the strike of the rocks (crosscuts). The cross section of the workings is mainly 5.8–6.4 m². Workings with a cross section of 6.4 m² are driven to great lengths, on the order of 800–1000 m, and the worked-out space is supported with timbering. Workings with a cross section of 5.8 m² are driven to a length of about 30 m (crosscuts) without support. The blastholes are drilled with modern hand-held drilling machines of the PR-24L and PR-30LU types, using P-18LA and P-17LA pneumatic supports. As the explosive, detonit YuA is used everywhere, in cartridges 32 mm in diameter and with a cartridge weight of 200 g. The method of blasting is by fuse. Rock removal is carried out with PML-5MO and PPN-1s machines. Loaded mine cars are delivered to the dump by AK-2U battery locomotives.
Experimental studies aimed at investigating the influence of various factors on drilling-and-blasting performance indicators were carried out in two stages. At the first stage, studies were conducted to determine the degree of influence of the cut design on blasting operations.
When workings were driven across the strike of the rocks, incomplete outlining of the excavation occurred; pillars of unbroken rock remained at the floor or the roof of the working, depending on the direction, relative to the axis of the main working, in which the crosscuts were driven. In view of the fact that the dip of the rocks is not vertical but at an angle of 70–78°, it was decided to check whether the design of the cut being used was playing a negative role here. In all workings a vertical-wedge cut is used, irrespective of how the workings are driven relative to the bedding of the rocks. A lower cut was proposed when the rocks dip toward the face, and an upper cut when they dip away from the face. The experimental studies were carried out only with the use of the lower cut. The results are given in Table 1.
Analyzing the data of the table of experimental studies, the following conclusion can be drawn:
Table 1
| Number of measurements | Cut | Number of holes | Hole depth, m | Advance per blast, m | HUF | Explosives consumption per 1 linear m of advance, kg |
|---|---|---|---|---|---|---|
| 16 | Vertical-wedge | 13–14 | 1.4 | 1.20 | 0.86 | 13.9 |
| 16 | Lower | 13–14 | 1.4 | 1.3 | 0.93 | 13.7 |
The use of the lower cut when rock falls onto the face makes it possible to increase the hole utilization factor by 7% due to complete outlining of the working over the entire cross section of the face breast. At the second stage of the experimental studies, the influence of stemming on blasting-performance indicators was determined.
When exploratory mine workings are driven by drilling-and-blasting methods, the charge is placed in a charge chamber (hole), filling some part of it, depending on the physicomechanical properties of the rock. After charging, the remaining part of the hole is filled with some dense material (stemming), which provides sufficient resistance to the pressure of the explosion gases and prevents their escape through the mouth of the hole, premature lowering of their pressure, and reduction of the useful mechanical effect of destruction. In blasts without stemming, or with insufficient stemming, part of the gases formed during the explosion is discharged into the atmosphere; as a result, part of the potential energy contained in the explosives is lost during conversion into mechanical work, and the calculated charge size proves insufficient to obtain the specified blasting work. In this case the work can be performed either by increasing the charge or by using good, dense stemming.
The fact is that during an explosion the pressure acts in all directions with equal force. In the absence of stemming, the gases are directed along the hole and escape into the atmosphere. Although gas formation takes place over a short interval of time, nevertheless the portion of gases that has managed to leave through the hole has a substantial effect on the results of the blast. If, immediately after the charge, dense, good stemming is placed, then the explosion gases, having no free outlet into the atmosphere, develop the greatest pressure and perform the necessary useful work.
To determine the degree of influence of stemming on blasting operations, experimental studies were carried out under production conditions. At the first stage of the studies, measurements were made of hole length and advance per blast when blasts were carried out without the use of stemming. The hole utilization factor and the explosives consumption per 1 linear m of advance were calculated. At the second stage, the same measurements were made and the same drilling-and-blasting parameters were calculated, but this time when blasts were carried out with stemming. The results of the experimental studies are given in Table 2.
Table 2
| Blasting conditions | Number of blasts | Average hole depth, m | Average advance of the face per blast, m | HUF | Explosives consumption per 1 m of advance of the mine working, kg |
|---|---|---|---|---|---|
| Without stemming | 29 | 1.48 | 1.33 | 0.90 | 12.44 |
| With stemming | 24 | 1.43 | 1.36 | 0.950 | 11.14 |
Analyzing the data in the table, we see that the consumption of explosive per 1 linear m of drift is reduced by 1.3 kg. With an annual work volume of 2000 linear m (the 1969 plan of the Perevalninskaya party of the Northern Expedition), the annual consumption of explosive is 2600 kg. At a cost of 470 rubles per 1 t of detonite, the expenditure in monetary terms is 1222 rubles.
The utilization coefficient of the blasthole when blasting stemming-filled holes increases by 5%; i.e., instead of an advance per blast of 1.3 linear m (according to the data of the Northern Expedition report), an advance of 1.365 linear m per blast can be achieved. The number of cycles for an annual work volume of 2000 linear m is reduced from 1538.5 to 1470.6, i.e., by 67.9 cycles. With three cycles per day, the party loses approximately, due to a 5% reduction in the blasthole utilization coefficient, 15–20 days per year.
As a result of the experimental studies, it was proposed:
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When driving workings across the strike of the rocks, use a lower or upper cut depending on the direction of dip of the rocks relative to the face.
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Take the blasthole filling coefficient “\(\alpha\)” as 0.8 for cut holes and 0.7–0.75 for contour holes, provided that blasting operations are carried out using stemming.