Smooth blasting is mainly for the blasting of a layer of rock mass in the surrounding area. At the same time as the rock mass is broken, a smooth and flat boundary should be formed. The main blasting parameters are minimum resistance line, gutter method, number of blastholes, blasthole spacing, and line charge density. The determination of the main parameters of smooth blasting should not only meet the technical requirements of smooth blasting, but also ensure the rapid tunneling needs. Technically feasible, it is necessary to reduce the disturbance to the surrounding surrounding rock, to over-excavate small, to reduce the amount of explosives, and to meet the requirements of mechanical slag.
First, the grooved eye
The correct arrangement of the grooving eyes can ensure the blasting effect of the slotting of the working surface, create favorable conditions for the smooth blasting, and open the blasting free space. From the blasting principle of the long strips, it can be known that in order to obtain a satisfactory grooving effect at the same time as the footage is ensured, that is, the rock breaking and the slag slag are not in conflict, the empty eye, that is, the artificial free surface, is often arranged in the design grooving. Therefore, in designing the gutter, in order to obtain satisfactory results, the parameters of diameter, number, blasthole spacing, and charge concentration must be carefully selected.
The grooving eye is arranged in the middle and lower part of the excavation section, and adopts the form of a straight-eye spiral grooving cloth hole, that is, a hole is arranged at the position of the boring section of the excavation section, and each of the charging blastholes is spirally arranged around the hole, the distance is Incremented in turn, the charging segment is sequentially incremented, the sequence is detonated, and the volume of the cavity is sequentially expanded. The diameter of the drug roll is 32 mm.
(1) Number of holes
The number of empty eyes required for blasting of the working face, that is, the number of small-diameter open eyes, is determined according to the occurrence state of the rock mass at the working face and the size of the artificial free surface required for lithology calculation. It can be obtained by the following empirical formula:
N≥2·L·A·B
In the formula:
N- is the number of empty eyes;
L- is the length of the working face blasthole, which is taken to be 1.6m;
A- is the empirical factor of blasthole detonation damage, generally taking 0.5~0.7, the maximum value when the eye is shallow (below 1.8m), and the small value when the eye is deep;
B- is the rock's strength correction value, which is 1/10 of the firmness factor f.
(2) Relationship between the diameter of the eye and the spacing of the holes
From the relevant information: α = (π / 4) (D 2 + d 2 ) (k + 1) / (D + d) (k-1)
In the formula:
α- # 1 slot to center distance hole, mm;
K- is the rock swell factor, taking 1.5;
D- is 1 # slot diameter, take 42mm;
D- is the diameter of the blasthole, mm.
When calculating the groove resistance line, that is, the groove hole and the hole spacing, the hole diameter is performed according to the condition of the single hole.
(3) grooving method
Select the straight-eye spiral grooved hole form.
(4) Calculation of line charge density
According to the law of small-section rock clip fabrication and single-free rock breaking, it is determined that when the depth of the eye is 1.8m, it is effective to break rock and throw slag to form the funnel space, and the line charge density is larger than other blastholes. The formula is as follows:
q=2d 2 (p·c) 1/3
In the formula:
Q- is the line charge density, kg / m;
D- is the diameter of the blasthole 0.042m;
p·c- is the rock wave impedance, kg/m 2 ·s.
Second, the peripheral eye
(1) Peripheral eye spacing
The main reason for determining the quality of smooth blasting is the peripheral eye. According to the smooth blasting stress wave interference failure theory and the air wedge effect of the detonation high pressure gas, the principle of the roadway contour can not be formed by the expansion of the crack. The eye distance is calculated by the following formula:
E≤2K 1 R 0 (2h pressure / h pull +1) 1/2
In the formula:
E- is the peripheral light burst eye distance;
K 1 - is a multiple of the radius of the damage on the axis of the light bursting eye, generally taking K 1 = 2 ~ 3, and its value increases as the hardness of the rock increases;
R 0 - is the radius of the blasthole, taking 0.021m;
h pressure / h pull - is the compression ratio of the rock, take 10 ~ 20.
(2) Minimum resistance line of peripheral eyes
According to the principle of blasting rock breaking, in order to reduce the amount of super and undercut, the relationship between the minimum resistance line and the peripheral spacing of the peripheral eye is expressed by the density of the blasthole. According to the data analysis, the density of the blasthole is 0.7 to 1.0. When the working face rock layer is soft, take a small value, and vice versa. In practice, we mostly take around 0.86.
(3) Peripheral eye line charge density
Smooth blasting requires that the detonation energy should both collapse the photo-explosive layer rock mass and form a through-crack between adjacent two peripheral eyes without causing damage to the surrounding rock. The line charge density can be calculated by the following formula:
Q=72.5R 0 E 1/2 f 1/3 /3D 2
In the formula:
Q- is the line charge density, kg/m;
R 0 - is the radius of the blasthole, taking 0.021m;
F- is the firmness factor of the rock, taking 6-8;
D- is the explosive detonation speed, km/s.
When the diameter of 2 # rock ammonium nitrate explosive is 32mm; the detonation speed can be 2600m/s.
In practical application, the following points should also be grasped: 1. According to the change of surrounding rock, the light explosion parameters should be adjusted in time. During the construction, in different sections of the same tunnel, there are often actual conditions such as uneven hardness, different degrees of weathering, and different joint development. The light explosion parameters should also be adjusted accordingly. Specifically, for the case where the rock becomes soft, the weathering is severe, or the joint development occurs, the peripheral eye distance (E) and the line charge density (Q) should be appropriately reduced, and vice versa. 2. While following the design principles of other blastholes, it is necessary to fully consider the blasting range of the front blasthole and the use of the created free surface, especially in the sulcus and the peripheral eye. 3. Strengthen the precision of drilling the eye and improve the rock drilling efficiency. Compared with the straight eye groove and the slanting eye groove, since the blasthole is perpendicular to the face of the face, the blasthole is not limited by the width of the excavation section, the blasthole drilling direction is easy to control, and the blasting slag heap is concentrated, etc. The reason is that the blasting design adopts a straight-eye spiral groove, which requires high precision and spacing error, and requires the construction of personnel with skilled drilling technology. 4. The simultaneous nature of the light face detonation is very important. Only the adjacent holes can be detonated at the same time to form the superimposed stress, and the combined stress is formed in the direction of the vertical center line, eventually forming a smooth failure surface. Therefore, a high-precision millisecond detonator should be selected to reduce the detonation. jet lag.
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