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41Scientific Journal Impact Factor
WALL CONTROL AND CONTOUR BLASTING TO ENSURE THE
STABILITY OF THE QUARRY BOARDS WHEN OPERATING DRILLING AND BLASTING WORKS
Shamaev M.K., Lecturer of the Department of Mining, Almalyk Branch Tashkent State Technical University named after Islam Karimov.
Melnikova T.E., Lecturer of the Department of Mining, Almalyk Branch Tashkent State Technical University named after Islam Karimov.
Abstract: The main limitation imposed on the conduct of drilling and blasting operations in the near-contour zone of a quarry is the need to protect the sides of the quarry and engineering structures on the sides from the seismic effects of massive explosions. As practice shows, the most effective and proven method of protecting the pit walls is the use of contour blasting, skewing the pit walls, preceding a massive explosion. A method for the formation of stable slopes of the sides of a quarry, an excavator method for sloping ledges on the limiting contour of a quarry and a method for initiating borehole charges of explosives in the near-contour zone of a quarry have been developed and introduced into the industry.
Keywords: Open pit edge zone, seismic impact, massive explosion, contour blasting, pit wall stability, open pit contour, bank slope work, borehole charges, explosives, pit wall protection.
Аннотация: Налагаемым основным ограничением на ведение буровзрывных работ в приконтурной зоне карьера является необходимость предохранения бортов карьера и инженерных сооружений на бортах от сейсмического воздействия массовых взрывов. Как показывает практика, наиболее эффективным и опробованным методом защиты бортов карьера является применение контурного взрывания, проведение заоткоски бортов карьера, предшествующей массовому взрыву. Разработаны и внедрены в промышленность способ формирования устойчивых откосов бортов карьера, экскаваторный способ заоткоски уступов на предельном контуре карьера и способ инициирования скважинных зарядов взрывчатых веществ в приконтурной зоне карьера.
Ключевые слова: Приконтурная зона карьера, сейсмическое воздействие, массовый взрыв, контурное взрывание, заоткоска уступов карьера, контур карьера, устойчивость бортов карьера, скважинные заряды, взрывчатые вещества, предохранение бортов карьера.
Scientific Journal Impact Factor
INTRODUCTION
For all quarries and opencast coal mines, and even within the same deposit with complex geological conditions, there is no uniform technology for sloping benches that would be acceptable. Various factors need to be considered such as direction of cracks, rock stratification, presence of deformed zones, etc. And also the properties of rocks, which characterize their destructibility by drilling and blasting, are of great importance.
The research process used the methods of objectivity, logic, analysis and synthesis of scientific knowledge. A significant number of technological schemes allows them to be subdivided according to various criteria. V.N. Popov, I.I. Popov, R.P. Okatov divided them into two groups, namely, the joint doubling - the alignment of the ledges and the separate outward slope of the sub-ledges. The slope technology has two main goals: increasing the slope angle of the ledge in order to reduce the volume of overburden and maintaining the strength of the circumferential massif to ensure safe mining.
Consider the types of flow diagrams for ledges that have found wide application in practice:
- presplit blasting along the contour to the entire depth of the double ledge, followed by separate mining of the upper and lower sub-ledges by massive explosions;
- "smooth blasting", (the nature of this scheme is when the wells are drilled along the contour to the entire depth of a 30-meter ledge, but at the same time, the upper sub-ledge is blasted by the bump holes simultaneously with the lateral ones with a short deceleration between the rows, and for the lower sub-slope the lateral wells form a preliminary slit);
- with separate subbench wall control of inclined borehole;
- with separate vertical boreholes along the slope of sub-slopes with drilling of additional wells of variable depth on the design contour;
- with the wall control of double ledges using combined technological schemes.
The choice of technological schemes for wall control works is greatly
influenced by the geological structure and structure of the massif at the mined area, the strength of rocks and the characteristics of shear resistance at the contacts of rock sheets and cracks, the standing of the sides in the limiting position, the intensity of
REFERENCES AND METHODS
DISCUSSION AND RESULTS
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weathering and crumbling of rocks from the surface of the slopes, the technical characteristics used on enterprises of drilling rigs. The most effective way to increase the stability of ledges is contour blasting. There are two possible ways of blasting the charges of the contour row: before the blasting of the main crushing charges in the border zone (presplit blasting); after breaking off the border zone (smoothwall blasting).
Fig. 1. The effect of blasting a charge on a rock mass.
The explosion leads to crushing of rocks in the zone immediately adjacent to the explosive charge (crushing zone, Fig. 1). In the zone of intense cracking (zone of intense cracking, Fig. 1), closed cracks open and new ones are formed. Rock blocks are displaced relative to each other, and splits are formed on the upper platform. Rock blocks in this zone almost completely lose their conjunction and are kept in balance due to friction and engagement by block irregularities. Further, in the fracturing zone, rock mass disturbances manifest themselves in the form of crack opening and an increase in fracturing.
The width of this zone reaches 40-50 m. Since the displacements of the massif during the explosion are directed backwards - upwards, they are most unfavorable in the presence of systems of cracks falling towards the massif. The presence of such cracks with a fall of more than 32 - 360 can lead to the collapse of the cut blocks immediately after the explosion. Further into the massif, the rock does not receive residual deformations, the vibrations are elastic in nature (elastic vibration zone in Fig. 1.). The size of this zone significantly depends on the mass of the simultaneously exploded charge and the properties of the rocks. However, by their nature, the
oscillations are an additional load and therefore the benches, which are in an equilibrium state close to the limiting one, can be disturbed even at large distances from the place of blasting. An increase in the disturbance of the massif intensifies the weathering processes and accelerates the formation of rock sloughing.
Reducing the adverse impact of the explosion on the array can be achieved by:
- limiting the mass of the simultaneously exploded charge;
- the use of contour blasting of inclined wells, diagonal short-delay blasting schemes, the slope of the ledge along the cracks falling towards the mined-out area of the open pit.
Vibrations of the rock during the explosion are characterized by the rate of displacement. A displacement rate that does not cause deformation will be permissible 09per) under these conditions. It depends on the type of rocks that make
up the slopes and the rate of application of the load (Table 1).
Permissible vibration velocities for buildings and structures (in the absence of deformations in them) should not exceed 3 ^ 6 smS.
Table 1
Characteristics of the rocks composing the slope Permissible displacement rates, smS when exploding
multiple blasting single blast
Water-saturated sandy rocks 6 12
Loosely connected and with unfavorably oriented fracturing rocks 24 48
Strenght rocks 48 96
At the same time, the oscillation speed depends on the mass of the simultaneously exploded charge Q, the distance from the explosion site to a given slope r and the properties of the rocks composing the slope. Maximum permissible value of simultaneously exploded charge (kg):
where - permissible vibration speed (Table 1), sm/s; r - is the distance to the explosion site, m; K - is the coefficient of the influence of the rock (Table 2).
Table 2
Characteristics of the rocks composing the slope K values
averages for single explosions maximum at multiple explosions
Water-saturated sandy rocks (the depth of the water table is less than 5 m) 450 600
Sparsely connected non-watered rocks with unfavorably oriented fracturing 300 450
Strenght rock slopes 200 300
In case of short-delayed explosion, the action of each series is not superimposed on the next one, while ensuring the deceleration interval (ms).
T >2
1 зам — -¿J 5
where S - is the surface area of the slope per one borehole, m2; у - rock density, t/m3; q- specific consumption of explosives, t / m3.
An increase in the stability of ledges can be achieved by applying: a) diagonal short-delay blasting schemes; b) inclined charges for breaking rocks; c) contour blasting.
The use of diagonal short-delay blasting schemes (Fig. 2) reduces the width of the residual deformation zone in the upper part of the ledge by a factor of 1.5-2 as compared to linear blasting.
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o
0
Fig. 2. Diagonal short-delay explosion schemes: 0-8-number of deceleration stages
When mining is approaching the limiting ledge contour at a distance closer than 30-40 m, regardless of the chosen method of the slope, no more than two-row arrangement of charges with a diagonal short-delay blasting scheme should be used.
The use of diagonal short-delay blasting schemes and deviated wells does not require special additional costs. These methods are also very effective in improving the quality of rock breaking and crushing and can be recommended as permanent methods of drilling and blasting operations.
Contour blasting (Fig. 3) is used when setting the bench to its final position with a minimum harmful effect of the explosion on the condition of the slopes. This effect is achieved by reducing the amount of charge in the last row of wells. A number of inclined wells are drilled along the design slope contour with an interval of 0.8 - 2 m, preferably with a reduced diameter and oriented according to the design slope angle. Boreholes are charged with weakened explosive charges. There must be an air gap between the borehole wall and the charges. The charges for contour blasting are made in the form of a garland of explosive cartridges on a detonating cord. The lower part of the charge increases by 1 m.
not less than 12-15 dcharge
/
ö»' 11
Fig 3. Scheme of contour blasting.
Table 3 shows the approximate parameters of the contour charges in rocks of various hardness according to the scale of Professor M.M.Protodyakonov and at different distances between the wells of the contour row.
Table 3
Rock-hardness ratio Blasting ratio*, kg/m3 Charge mass of 1 running meter of borehole (kg) depending on the distance between contour boreholes
1 m 1,5 m 2 m
16-20 0,8-1 1,5 2,2 3,0
10-12 0,5-0,6 1,0 1,5 2,0
6-8 0,3-0,4 0,8 1,2 1,5
* The blasting ratio during technological blasting is an indirect characteristic of the strength of rocks.
CONCLUSION
Thus, the slope of the benches in the final position along cracks and other structural weakening, falling towards the mined-out area of the quarry, is necessary at angles of incidence of 400 and more. Wall control blasting is performed by blasting either inclined wells at an angle of incidence of cracks, or vertical wells of different heights. Breaking of the rock at the final contour of the quarry should be carried out by wells that do not have a subdrilling.
REFERENCES
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