Production explosion of open pit mine

The production blasting of open pit mines, that is, the deep hole blasting of the production steps of open pit mines.

In recent years, with the large-scale, high-efficiency and high-speed production capacity of open-pit mines, the amount of blasting required for step deep-hole blasting is increasing. For this reason, large-scale blasting methods such as multi-row hole differential blasting, millisecond anti-extrusion blasting and high-step blasting are widely used in open-pit mining at home and abroad. At present, many mines blast 5 to 10 rows and 200 to 300 blastholes each time. The amount of blasting ore is as much as 30 to 50×10 ⁴ t. The blasting scale of large-scale open pit mines at home and abroad listed in Table 1 clearly reflects this trend.

First, multi-row hole differential blasting

Multi-row hole differential blasting refers to the millisecond blasting with the number of rows above 4 rows and the hole depth >6m. This blasting method has a large amount of blasting at a time, and it has the advantages of earthquake reduction, control of blasting direction, full use of explosion energy and improvement of blasting quality. Therefore, at present, most of the open-pit mines at home and abroad have used multi-hole blasting in the production of blasting. In recent years, due to the continuous development of detonating equipment in China, the number of millisecond detonators has been increasing, and the quality has been continuously improved, especially with plastic detonating tubes as the main body, supplemented by non-electrical detonating shunts (also known as detonating four-way). The non-electric detonation system provides more favorable conditions for the development and application of multi-row hole differential blasting technology, and enables equal-interval multi-row millisecond blasting technology. Many mines have promoted and applied non-electrical detonation systems, which have achieved significant economic and safety benefits.

Table 1 Scale of deep hole blasting in open pit mines at home and abroad

(1) Multi-row hole differential blasting parameters

At present, the determination of the multi-row hole differential blasting parameters is mainly based on experience, and there is no mature theoretical derivation. The relationship between the parameters is shown in Figure 1.

Figure 1 Deep hole blasting parameters

H-step height; L-drilling depth; L ₁ - charge length; L ₂ - filling length; L'- ultra deep;

WD-vertical hole chassis resistance line; W-slant hole resistance line; c-step slope top to hole center distance;

--step slope angle; a-hole distance; b-row spacing

1, chassis resistance line WD

It is an important parameter affecting the effect of differential blasting in open pit mines. The value of the value is related to the diameter of the borehole, the diameter of the charge, the characteristics of the explosive, the density of the charge, the explosiveness of the rock, the degree of fracture required, and the height of the step. Its determination is based on empirical calculations under the premise of satisfying rock fracture conditions, safety conditions and charging conditions.

Determine the relationship between the chassis resistance line W _D and the step height h:

Vertical hole

W _D = (0.6 ~ 0.9) h

Tilt hole

W=(0.4~0.5)h

Where W _D - chassis resistance line, m;

W-oblique hole resistance line (ie minimum resistance line), m;

H-step height, m.

Determined by the relationship between the chassis resistance line WD and the diameter D of the borehole

W _D =53DK _B (△KH/γ) ^1/2

Where D-drilling diameter, m;

K _B - rock explosive coefficient, for explosive, moderately difficult and difficult to explode rocks, K _B values ​​are 1.2, 1.1 and 1.0 respectively;

â–³-charge density, t/m ³ ;

K _H - explosive conversion factor;

Γ-rock bulk density, t/m ³ .

Calculated according to the drilling charge conditions:

Vertical hole

Tilt hole

Where q ₁ - the amount of drilling per meter, kg / m;

Q-explosive unit consumption, kg/m ³ ;

E-hole filling factor, e=L ₂ /W _D ≥0.75;

L ₁ - charge length, m;

L ₂ - filling length, m;

P-super deep coefficient, p = L' / W _D = 0.15 ~ 0.35;

L'-drilled super deep, m;

M-drilling proximity coefficient;

L-drilling depth, m.

Calculate the results according to the above three conditions, take the minimum value, and check according to the safety conditions of the operation.

W _D ≥hctgα+c

The safety distance between the c-hole center and the top line of the step slope is generally c≥2.5~3m;

--step slope angle, degree.

When using differential blasting, it is necessary to consider the increased resistance line value W' of the corpus callosum, ie

W'=δp/Ks

Where W'-碴 body thickness is converted into an additional resistance line value, m;

Average thickness of δp-steroid, m;

K _S - Loose coefficient of the carcass after blasting.

2. Pitch a, row b and proximity coefficient m Pitch a and row b are two important parameters that control the effects of interaction between the boreholes. The relationship between them is:

First row of holes

a ₁ =m ₁ W _D

Rear hole

a ₂ =m ₂ b

Where m ₁ and m ₂ - are the adjacent coefficients of the front and rear rows, respectively, generally m ₁ ≤1, m ₂ ≥1, when the equilateral triangle is arranged,

m ₂ =1.15; when square hole, m ₂ =1;

a ₁ , a ₂ - are the spacing of the front and rear rows of holes, m.

The size of the proximity coefficient m has an important influence on the utilization of explosive energy. In the deep hole blasting of open pit mines in China, the proximity coefficient generally varies between 0.5 and 1.4. In recent years, in the multi-row hole blasting at home and abroad, the large-hole blasting technology is adopted from the second row of holes. According to some open-pit mine blasting experience, it is shown that the blasting quality can be improved by appropriately reducing the row spacing and increasing the hole spacing while keeping the bearing area S of each blasthole substantially unchanged. Its relationship is

Where S - the blasting area of ​​each borehole, m ² ;

Other symbols have the same meaning as before.

When the slanting line differential detonation is adopted, the drilling arrangement, the detonation order and the resistance line direction are changed, the row spacing between the detonating holes is reduced, and the hole spacing is increased, thereby increasing the m value of the adjacent coefficient.

3, drilling ultra deep L'

It refers to the depth of the hole below the horizontal portion of the stepped plate. Its value depends mainly on the nature and structure of the rock and is related to parameters such as the chassis resistance line, the diameter of the hole and the nature of the explosive.

The ultra-deep effect is to reduce the center position of the column so as to help overcome the resistance at the bottom of the step. For rocks with certain characteristics, if they are too deep or too deep, they will easily produce roots; when the depth is too large, not only waste drilling and explosives, but also reduce the amount of blasting, and because the center of the column is too low, it will The upper part of the step produces a large block and destroys the integrity of the rock mass on the surface of the next step, which makes it difficult to drill in the future. Generally, the drilling depth is deep and can be determined by pressing the test.

L'=(0.15~0.35) W _D

Or L'=(8~12)D

According to the experience of blasting in open pit mines in China, the ultra-deep value is generally 2.5-3.5 m in hard and difficult-explosive rocks, 2.0-3.0 m in medium-hard rock, and 0.5-2.0 m in soft rock.

4, filling length L ₂

The filling length has a great influence on the utilization of deep hole blasting explosive energy. If the filling length is insufficient, the explosive energy will flow straight out from the orifice, causing the rock mass to scatter and the blasting quality to be reduced. If the filling length is too large, not only the drilling hole is wasted, but also the large filling is easy in the filling section of the orifice.

When drilling a continuous charge, the filling length can be calculated as follows

L ₂ = (20 ~ 25) D

Or L ₂ =eW _D

Where e-filling coefficient, vertical hole e = 0.7 ~ 0.8; oblique hole e = 0.9 ~ 1.0.

5, the unit consumption of explosives q and the amount of charge per hole Q

Due to the ruggedness of the rock and the difference in the structure and structure of the rock mass, the explosive properties of the rock are different, and the consumption of the explosive unit is also different. The value can be determined experimentally according to different classification methods, or can be selected with reference to relevant design data.

At present, open-pit mines at home and abroad have a tendency to increase the consumption of explosives units, and increase the q value to improve the blasting effect and reduce the total production cost of open pit mines. Figures 2 to 3 illustrate the relationship between the unit consumption of explosives and the bulk rate and the total cost of mine operations.

Figure 2 Relationship between explosive unit consumption and bulk rate

1-explosive rock; 2-moderately difficult rock; 3-difficult rock

Figure 3 Relationship between explosive unit consumption and total operating cost

(under moderate rock conditions)

1, 2, 3 - corresponding to the aperture of 100, 200, 300mm

The determination of the charge Q per hole is generally calculated by the volume formula at home and abroad, ie

Front row of holes Q=qaW _D k

Rear row of holes Q=qabhK

Where Q-the amount of charge per hole, kg;

K-combined blasting, the coefficient of increase of the amount of pores in the rear row, generally K = 1.1 ~ 1.2;

The rest of the symbols have the same meaning as before.

(two) differential interval ι

The differential interval time refers to the interval between the two adjacent boreholes under the condition of millisecond blasting. It is the time factor that affects the blasting, which largely determines the effect of the millisecond blasting. The selection of the interval time is mainly related to the nature of the rock, the minimum resistance line, the crushing effect, the earthquake-reduction requirements and the detonating equipment. Reasonable differential interval should be based on the good rock crushing effect and high seismic efficiency.

Regarding the calculation of the differential interval time, although there are many calculation formulas proposed at home and abroad, so far, there is no recognized general calculation formula. According to the actual experience of various open pit mines in China, the interval between the differentials used is mostly between 25 and 75 ms. Take small values ​​in hard rock and take larger values ​​in soft rock.

At present, the millisecond electric detonators and non-electrical millisecond detonators produced in China have been produced to 20 segments, while the larger ones are the first 5 segments, followed by the 6-15 segments, and the interval between 5 segments is longer and longer (50 to 300 ms). The error is getting larger and larger (±10~±150ms). Therefore, when the millisecond electric detonator and the non-electrical millisecond detonator are used for the millisecond blasting, the number of detonation sections and the interval of the differential are limited by the number and precision of the detonator. A ground delay device that can be used in conjunction with a non-conducting squib, which can control the time difference between the non-electrical squibs and the non-conducting blasting device (ie, the detonating four-way), is used for the non-conductance detonation when the hole is extended. In the explosion system, the millisecond blasting is not limited in principle, and the millisecond blasting at equal intervals can be realized.

(3) Cloth hole method and initiation sequence

At present, there are basically two kinds of cloth hole methods for deep hole blasting in open-pit mines at home and abroad, namely triangular, square or rectangular cloth holes. The latter facilitates perforation, charging and filling mechanization.

The detonation sequence of multi-row hole differential blasting is various, and there are several schemes as shown in Fig. 4.

Inter-row sequence detonation scheme The detonation sequence of Figure 4a begins with the freedom of the step and starts from the front to the back. If the number of blastholes in the same row is large, in order to reduce the seismic effect, the same row of blastholes can be divided into several sections to detonate. The advantage of this detonation scheme is that the detonation network connection is simple, the explosion stacking agent is uniform, and the collapse line after the final row of holes is blasted is obvious and regular, and is favorable for overcoming the root. However, the shortcoming is that the blasting seismic effect is strong and the backlash effect is also large.

Figure 4b and Figure 4a are basically the same, except that the row spacing is reduced from the second row, the m value is increased, and the large-hole blasting is realized. In the last row of holes, the hole spacing is the same as that of the first row of holes in order to make the collapse line obvious, regular and not low. Practice has proved that this kind of cloth hole method can reduce the single consumption of explosives by 20% to 30% and reduce the bulk rate by more than 50%, thus greatly improving the blasting effect.

Figure 4 Multi-row hole differential blasting initiation sequence

1 to 9-detonation sequence; (a) the sequence is detonated; (b) the large hole is sequentially detonated from the row;

(c) slanting sequence detonation; (d) "V" shaped detonation; (e) wavy detonation;

(f) detonation of the middle gutter; (g) detonation of the wedge groove

The oblique sequence detonation scheme is shown in Fig. 4c, and the detonation sequence is from the front side of the explosion area, and the detonation is sequentially performed in the order indicated in the figure. The line connecting the detonation holes in the same section is oblique to the top line of the step slope. The advantage is that: due to the small number of detonation drill holes in the same section, the earthquake reduction effect is good; the adjacent sections are squeezed by the explosive rock bodies, and the crushing effect is good; the explosion pile is concentrated, and the front and back are small. At the same time, due to the change of the direction of the blasting force, in the case where the single-hole blasting area S is constant (in the figure: S=a'b', and a'b'=ab), the m value can be increased to realize the large hole. From the blast. Therefore, this program is widely used in open-pit mines at home and abroad, and has received good blasting effects. The disadvantage is that the rear hole is highly clamped and the collapse line is not obvious.

"V" shape (d in Figure 4) and wave shape (e in Figure 4) two detonation schemes, although the adjacent sections are more fully crushed and crushed by the explosive rock bodies, the blasting effect is good, and the explosion pile is concentrated. But the network connection is more complicated.

Intermediate or wedge-shaped trench detonation (Fig. 4f, g) is commonly used for trench blasting. In the middle trench detonation scheme, firstly, the middle row of the groove is detonated to form a groove-like free surface, and then the rows of holes on both sides are detonated. Since the middle jaw groove is made of a larger clip, the hole spacing is generally 20% smaller than the normal hole, the ultra deep is increased by 5% to 10%, and the dose is increased by 20% to 25%. The wedge-shaped trench initiation scheme is a detonation scheme used to reduce the clamping of the middle slotted hole, which is basically similar to the "V" shaped initiation scheme.

The advantages of using multi-row hole differential blasting in open pit mines are:

1. A large amount of blasting can reduce the number of blasting and avoiding time, and improve equipment utilization;

2, improve the quality of blasting, the bulk rate is reduced by 30% to 50% than single-row hole blasting;

3. Increase the utilization rate of perforating equipment by about 10% to 15%, which is due to the increase in working time utilization rate and the decrease in the number of operations of punching equipment in the punching action area after blasting;

4. Improve the efficiency of mining and transportation equipment by about 10% to 15%.

Figure 5 shows the effect of the number of blasting rows on the blasting effect. It can be clearly seen from the figure that multi-row hole blasting has great advantages.

Figure 5 Effect of the number of blasting rows on the blasting effect

1-excavator efficiency (m ³ /m ³ bucket capacity · h); 2 - rig efficiency (m / Taiwan · h);

3-transport efficiency (m ³ /m railway); 4-bulk rate (%)

However, multi-row millisecond blasting requires timely preparation of a sufficient number of boreholes, which necessitates the use of highly efficient perforating equipment. The work of multi-row hole differential blasting is concentrated, and in order to blast in time, the charging and filling work should be mechanized.

Second, multi-row hole differential extrusion blasting

Multi-row hole differential squeezing blasting is a type of blasting that is left in front of the step work, and a reasonable differential interval time and detonation sequence is selected, as shown in Fig. 6.

Figure 6 Schematic diagram of differential extrusion blasting

A-vertical blasthole; b-inclined blasthole

This kind of blasting creates conditions for extrusion due to the presence of ramming piles. On the one hand, it can significantly increase the explosive stress in the rock, prolong the explosion action time, improve the utilization rate of explosive energy and increase the explosive unit consumption. Blasting effect; on the other hand, it can control the width of the explosion and avoid the scattering of ore.

According to the experience of using differential blasting at home and abroad, we should pay attention to the following problems.

(1) 碴 pile thickness δ and loose coefficient Ks

The thickness of the pile determines the strength of the rigid support during extrusion blasting. Suitable thickness of the pile should be able to maximize the energy of the explosive, which can be calculated according to the M, φ, Drukov formula

Where δ-碴 heap thickness, m;

K-explosive energy utilization coefficient, generally 0.04 ~ 0.2;

E-rock elastic modulus, Pa;

E ₀ - Explosive energy of unit explosives, J/kg;

The rest of the symbols have the same meaning as before.

The stress wave of the blasting blast is partially reflected into the tensile wave at the interface of the rock mass and the pile to continue to destroy the rock mass, and part of it is absorbed into the pile by the wave form. Therefore, under the premise of ensuring the extrusion of the pile, to increase the proportion of the reflected wave, it is necessary to make the stack loose. The ratio of the density of the original rock to the density of the pile is called the loose coefficient of the pile. According to domestic and international experience, the loosening coefficient of the pile should be kept between 1.15 and 1.4. If the looseness coefficient is too small and the stress wave passes too much, it is easy to compact the pile and form a hard wall, which affects the working efficiency of the excavator. When the pile thickness is too large and the looseness coefficient is too small (Ks<1.15), it must be increased. The amount of charge in the first row of holes or the mesh parameters of the first row of holes can be reduced to ensure the effect of extrusion blasting.

(2) Blasting distance B1

The rushing distance of the blasting pile is closely related to the thickness of the tamping pile. As the thickness of the ramming pile increases, the rushing distance of the blasting pile decreases. Figure 7 shows the relationship between the thickness of the pile and the distance of the burst. In order to ensure the working surface of the step, the forward distance of the pile can be calculated according to the following empirical formula.

Where B ₁ - bursting forward distance, m;

The average thickness of the top of the S-碴 pile, m;

D-drilling diameter, m;

Γ-rock bulk density, t/m ³ .

Fig. 7 Relationship between the thickness X of the pile and the distance B ₁ of the pile

(3) Dosage distribution and pore network parameters

The first row of holes in the multi-row hole differential blasting blasting will cause a large transmission wave loss due to close contact with the ramming pile, and it is necessary to push the tamping pile to create space for the rear row blasting. Therefore, it is necessary to increase the explosive energy of the first row of holes by 30% to 40%, that is, the first row of holes should increase the hole depth, reduce the resistance line or the hole distance, increase the charge amount or use a high-power explosive. In the blasting of the last row of holes, the looseness coefficient of the pile directly affects the mass of the next cycle of extrusion blasting. In order to loosen this part of the pile, the last row of holes also increases the explosive energy. To this end, the hole spacing or row spacing should be reduced by 10% to increase the total charge of the rear row of holes or to use high-power explosives, and the interval between the differentials should be extended by 15% to 20%.

Except for the first row and the last row of holes, the hole mesh parameters of the multi-row hole differential blasting blasting are the same as the multi-row hole blasting.

(4) Differential interval

Since the blasting blasting pushes the front pile, the blasting interval is longer than that of the ordinary blasting. If the interval is too short, the pressing effect is not enough, and the blasting will be limited; on the contrary, if the interval is too long, the pushed space will be filled by the broken ore and will not function as it should. Practice has proved that the interval time of multi-row hole differential blasting is 30%~50% larger than ordinary millisecond blasting. The differential time interval commonly used in open pit mines in China is 50-100ms.

In order to improve the blasting effect, the number of drilled holes in the blasting should be at least 4 rows or more.

Compared with millisecond blasting, the advantages of differential blasting blasting are:

1. The rock crushing effect is better. This is due to the presence of the front stack, so that the explosive energy is fully utilized and additional crushing action occurs under the squeeze of the stack;

2, the explosion heap is more concentrated. Due to the action of the pile, the rushing distance is small. According to domestic and international experience, when the thickness of the pile is 10~20m, the pre-burst distance is generally not more than 20m. For open pit mines that are transported by rail, they can be removed before blasting, thus improving the efficiency of the loading and transport equipment.

The disadvantages are:

1. The consumption of explosives is large, 20% to 30% more than the general multi-row hole differential blasting;

2, the height of the explosion pile is large, especially when the thickness of the pile is reserved to hinder the development of the pile, it may affect the safety of the equipment.