JP3065871B2 - Blasting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blasting method for crushing an object to be crushed, such as bedrock or blast furnace residual iron or concrete, by blasting.

[0002]

2. Description of the Related Art Conventionally, in order to crush an object to be crushed such as a bedrock by a blasting method, a blasting hole having a circular cross section of a predetermined depth is provided at an appropriate interval in a portion to be crushed. A blasting method has been adopted in which an explosive is loaded in the blast and then blasted to generate cracks in all directions from each blast hole. Furthermore, in such a blasting method, since the direction of the crack from the blasting hole is uncertain and efficient crushing cannot be expected, a notch is formed on the hole wall surface of the blasting hole, and stress concentration occurs at the notch portion at the time of blasting. In some cases, the direction of the crack is determined.

[0003]

However, the notch is formed by the blade at the same time as the hole is formed by using a piercing rod having a notch forming blade projecting from the outer peripheral surface. Not only does the installation work take time, but also, for example, when drilling a rock, the hole wall excavated by the rod tip bit has an uneven surface. Even if a notch can be cut into the convex surface of the hole wall by the blade body, a notch cannot be formed on the concave surface, and
Since the correction cannot be performed, the notch is formed discontinuously in the length direction of the blast hole, and the depth thereof is also non-uniform, so that there is a problem that it is impossible to form a crack with high accuracy. An object of the present invention is to provide a blasting method capable of completely solving such a problem.

[0004]

In order to achieve the above object, a blasting method according to a first aspect of the present invention is characterized in that a cross section is elongated at a substantially central portion of a planned excavation surface of a crushed object such as a bedrock.
A long hole- shaped borehole is drilled to a desired depth, and in the planned excavation plane on both sides orthogonal to the longitudinal direction in the cross-sectional shape of the borehole, the length in the longitudinal direction in the cross-sectional shape of the borehole is defined as one side. Toko
With two other virtual sides going outward from both ends of one side
The cross section is larger than the above bore hole in the equilateral triangle formed
Contact Keru the shape of the longitudinal direction of the shorter cross-sectional slot shape the length of the cross-sectional shape blasthole longitudinal borehole cross-sectional shape
The drilling holes are drilled to a desired depth in a state parallel to the longitudinal direction.Furthermore , blast holes having a long hole shape in section are provided at predetermined intervals outside the blast holes in the planned excavation plane at predetermined intervals. Each blast hole is drilled to a desired depth with the longitudinal ends of the cross-sectional shapes of adjacent blast holes facing each other, and explosives are loaded into each blast hole to form a blast hole close to the borehole. It is characterized by being blasted sequentially.

Further, the blasting method according to the second aspect of the present invention is characterized in that a blasting hole having a long cross section and a small hole having a circular cross section are formed along an outer peripheral edge of a planned excavation surface of an object to be crushed such as a bedrock. Are alternately drilled to a desired depth at predetermined intervals and in a state in which the longitudinal direction in the cross-sectional shape of the elongated hole-shaped blast hole is oriented in the circumferential direction of the outer peripheral edge of the planned excavation surface, and furthermore, these blast holes and On the planned excavation surface surrounded by the hole row composed of small-diameter holes, there is a constant interval inward from the hole row, and blast holes having a long hole cross section are formed at predetermined intervals so as to be along the hole row. A blast hole row is formed by drilling to a predetermined depth, and thereafter, the blast holes in the hole row composed of the blast holes and the small-diameter holes are charged and blasted, and then the inner blast hole row is formed. It is characterized by blasting.

[0006]

When an explosive is charged into a blast hole having a long cross-sectional shape and blasted, a crushing force is concentrated in the short direction of the cross-sectional shape of the hole and acts to cause a crack in a longitudinally extending direction. . Then, a plurality of blast holes are formed in a longitudinal direction in the sectional shape.
Since the ends in the direction are opposed to each other and drilled at regular intervals in the crushed object, cracks are surely generated between adjacent blast holes, and all the blast holes are continuous by this crack. Thus, the object to be crushed can be efficiently crushed.

Further, according to the first aspect of the present invention,
The cross section provided at the approximate center of the planned excavation surface is an elongated slot
When the blasting Jo borehole blasthole adjacent on both sides of, emitting Yabuana, at both sides of the borehole in an equilateral triangle plan excavation plane to one side of the length of the long side direction in the borehole cross-sectional shape because are bored with being directed parallel to the longitudinal direction <br/> direction with respect to the longitudinal direction of the borehole cross-sectional shape in its cross-sectional shape, the both ends in the longitudinal direction of the both end portions in the sectional shape of the blasthole Cracks are generated intensively between both ends in the longitudinal direction in the cross-sectional shape of the borehole facing the portion, and the blasting hole and the crushed object surrounded by the crack and the borehole can be efficiently excavated and removed. Next, when the outer blast holes are blasted, cracks are intensively generated between the longitudinal ends in the cross-sectional shape of the adjacent blast holes in the same manner as described above, and the crushed material surrounded by the blast hole rows and the cracks is formed. Excavation and removal can be performed efficiently.

According to the second aspect of the present invention, since the outermost blast hole row is provided with holes between adjacent blast holes, the cross section of the blast hole when the blast hole is blasted. The cracks are concentrated from the longitudinal end of the shape toward the holes, and therefore, the space between adjacent blast holes is continued by the cracks through the intermediate holes, so that the number of blast holes and the explosive Not only can the amount of use be reduced, but also accurate excavation along the outer peripheral edge of the planned excavation surface becomes possible. Next, the inner blast hole array is blasted to make the cracks between the blast holes continuous, and the planned excavation surface is excavated to a predetermined depth.

[0009]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a method of excavating a tunnel in a rock as a material to be crushed 1 by the blasting method of the present invention. The blasting holes 2 having a long cross section at regular intervals along the outer peripheral edge of a planned excavation surface 1a of the tunnel. The first blast hole row A1 is formed by piercing the end of the cross section in the longitudinal direction to a desired depth in a state in which the ends in the longitudinal direction face each other in the circumferential direction of the outer peripheral edge of the planned excavation surface 1a. An arc-shaped second blasting hole row B1 and a third blasting hole row C1 are formed in parallel with the outer peripheral edge of the planned excavation surface 1a at predetermined intervals sequentially inward from the first blasting hole row A1. The second blast hole row B1 and the third blast hole row C1
Similarly to the first blast hole row A1, the blast holes 2 having a long hole shape in cross section are formed at predetermined intervals by drilling the blast holes 2 to a desired depth with their longitudinal ends in the cross section facing each other. You.

Furthermore, substantially the same borehole 3 of the elongated hole-shaped cross-section is not elongated in the longitudinal direction in the center portion of the crushing part surrounded by the third blasthole column C1 of the innermost to the blasthole 2 and the tunnel longitudinal direction Contact to the cross-sectional shape of the bore hole 3 with bored to a depth
The third blast holes on both sides perpendicular to the longitudinal direction
In the planned excavation surface 1a inside the row C1, the length in the longitudinal direction in the cross-sectional shape of the borehole 3 is defined as one side.
One side and two other virtual sides going outward from both ends of this side
The bore is located in the planned excavation surface of an equilateral triangle
Blasthole 2b short <br/> cross slot shape of the longitudinal lengths of the cross-sectional shape than the holes 3, the length in the cross-sectional shape 2b
The hole is drilled so that the hand direction is parallel to the longitudinal direction of the sectional shape of the borehole 3.

The blast hole 2 having a long hole shape in cross section as described above,
For example, as shown in FIG. 3 , a plurality of rods 20 each having a bit 21 attached to the distal end are juxtaposed with the above-mentioned bids 21 having a diameter larger than the rods 20 being alternately shifted in the front-rear direction. When viewed from the front, a piercing tool is used in which the bits 21 and 21 of the adjacent rod 20 have a structure in which the opposing portions thereof are overlapped with each other. To a desired depth. It is desirable that the major axis of the blast hole 2 is formed at least twice as large as the minor axis.

In order to excavate the cross section of the planned tunnel by loading and exploding the explosive into each of the blast holes 2 thus drilled, first, the blast holes 2 on both sides of the borehole 3 are required.
b, and then loaded with explosives to blasting to 2b, cracks blasthole 2b by the blast, from both ends in the longitudinal direction of 2b cross section longitudinal intensively toward both ends in the cross-sectional shape of the borehole 3 Blast hole 2b and bore hole 3 generated
Are continuous due to cracks. The rock part surrounded by the crack, the blast hole 2b and the borehole 3 is excavated and removed.

Next, a third row of blast holes C1, a second row of blast holes B
1, in order from the first blast hole row A1, from the inside to the outside, blast each blast hole 2 of the blast hole row, excavate and remove the rock part surrounded by the blast hole 2 and the crack, and It excavates a tunnel. In addition, the blast line as above
Blasting may be performed with a short time difference in the order of 2b, C1, B1, and A1.

FIG. 2 shows another embodiment of the blasting method according to the present invention. A blasting hole 2 having a long cross section and a small hole 4 having a circular cross section are formed along the outer peripheral edge of the planned tunnel excavation surface. The first hole row A2 is formed by alternately piercing the blast hole 2 to a desired depth in a state where the longitudinal direction in the cross-sectional shape of the blast hole 2 faces the circumferential direction of the outer peripheral edge of the planned tunnel excavation surface at predetermined intervals. From the first hole row A2, arch-shaped second blast hole rows B2 and third blast hole rows C2 are drilled inward at regular intervals in order, and furthermore, the innermost third blast hole row C2 is formed. A borehole 3 having a longitudinally elongated slot shape is formed in the center of the enclosed crushed portion to a depth substantially equal to the blast hole 2 in the lengthwise direction of the tunnel, and a sectional shape is formed on both sides of the borehole 3. the length in the cross-sectional shape of the bore hole 3 the longitudinal direction of
Explosion holes 2c, 2c having a long cross section are formed in the hand direction. Note that these second, third blasthole column B2, C2 and borehole 3 and both sides of the blasthole 2c, a method of drilling and 2c are the same as those of shown in FIG. 1.

In this blasting method, the interval between the blast holes 2, 2 adjacent via the small-diameter holes 4 in the first hole row A2 is larger than the interval between the blast holes 2, 2 shown in FIG. The small hole 4 having a circular cross section is formed at an intermediate portion between the blast holes 2 and 2 to a depth substantially equal to that of the blast hole 2. That is, the blasting holes 2 and the holes 4 are formed alternately, and the distance between the opposing ends of the blasting holes 2 and the holes 4 is shorter than the longitudinal length of the cross-sectional shape of the blasting hole 2. ing.

In order to excavate the cross section of the planned tunnel by loading and exploding the explosive into each of the blast holes 2 thus drilled, first, the excavator is provided along the outer peripheral edge of the excavation surface of the planned tunnel. Blast each blast hole 2 in one hole row A2. Cracks due to this blast are intensively generated from the blast holes 2 toward the holes 4, and the adjacent blast holes 2, 2 are continuously connected by cracks through the intermediate holes 4, and the outer peripheral edge of the excavation surface of the planned tunnel A gap is formed along the line, which interrupts continuity with the outer rock. At this time, the holes 4 serve as passages for the vaporized explosives when blasted to escape.

Next, the blast holes 2c, 2c provided on both sides of the borehole 3 are blasted to generate cracks communicating with the upper and lower ends of the borehole 3, and the rock part surrounded by the blast hole 2c and the borehole 3 is removed. Drill and remove. Thereafter, the blast holes 2 of the third blast hole row C2 and the second blast hole row B2 are sequentially blasted to excavate and remove the rock mass surrounded by the blast holes 2 and the cracks by using the already removed space. Then, a tunnel of a certain length is excavated.

In each of the blasting methods described above, the explosive may be directly loaded into the blasting hole 2 to a desired depth and then blasted. However, a gap is formed between the explosive and the hole wall of the blasting hole 2 so that a hole is formed. As shown in FIG. 4, the explosive 7 loaded into the blasting hole 2 and the lead wire 8 of the explosive 7 are drawn out of the hole, and the blasting force of the blasting hole 2 cannot be transmitted efficiently. After filling the gap 10a with a filler 10a such as sand, it is preferable to blast or use a bag body 9 which expands by injecting the liquid 10 as shown in FIGS.

As described above, when the explosive 7 is blasted through the lead wire 8 in a state in which the gap between the explosive 7 and the hole wall of the blast hole 2 is filled with sand, liquid, or the like, the blasting force is surely increased by the filler. The crushed object 1 can be efficiently crushed. Explosive 7
The blasting force acts intensively in the short side direction in the cross-sectional shape of the blast hole 2 having a long cross-sectional shape with a short distance from the blast hole 2, and the opposing long sides are separated by the blasting force and concentrated in the longitudinal extension direction. Cracks occur.

As described above, sand may be used as the filler, but if the bag 9 having flexibility is used, the explosive 7 can be efficiently loaded. That is, the explosive 7 is inserted and fixed in the front end portion of the bag 9 in the closed state.
Is inserted into the blast hole 2, and then the liquid 10
Is injected and filled to inflate the bag body 9 so that the bag body 9 is brought into close contact with the hole wall of the blasting hole 2 and then blasted. As a means for fixing the explosive 7 in the bag 9, a hook-shaped explosive locking device is provided on the inner surface of the tip of the bag 9, or a velvet type fastener that engages with the explosive 7 is attached. Alternatively, a string for explosive connection may be attached.

As shown in FIG. 8, the bag 6 has a cylindrical shape having a length equal to that of the blasting hole 2 and a slightly longer or shorter diameter than the cross-sectional shape of the blasting hole 2. The front end side is sealed, and a charging port 9b that can be sealed by a fastener or other appropriate means is provided in the center of the rear end wall 9a, and the liquid is injected into an appropriate place. A liquid inlet 9c that can be connected to the hose 11 is provided. further,
At least one (two in the figure) rigid rod-shaped core material 12 is fixed to the peripheral wall of the bag body 9 in an embedded state in which the exposed surface thereof is flush with the outer peripheral surface of the bag body 9 over the entire length. It is.
The bag body 9 is made of a synthetic resin sheet material or a water-impermeable sheet material obtained by coating a fabric with a waterproofing agent.
When a high-temperature furnace wall such as a blast furnace is to be destroyed, it is formed of a refractory heat-resistant fiber such as a ceramic cloth.

When the bag 6 is not used, as shown in FIG. 9, the core 12 can be contracted in the width direction and the thickness direction by using the core material 12 as a holding portion, so that the bag 6 can be easily handled. Is loaded with the explosive 7 and inserted into the blast hole 2. At this time, the bag body 9 can be smoothly inserted into the blasting hole 2 by the rigid rod-shaped core material 12 and the bag body 9 is contracted even if the blasting hole 2 is slightly bent or the wall of the hole has irregularities. The insertion work can be easily performed.

After inserting the bag body 9 into the blast hole 2 in this way, the charging port 9b is sealed. Thereafter, as shown in FIGS. 5 and 6, a liquid injection hose 11 such as water is inserted into the liquid injection port 9c. Connect and bag 9
When the liquid 10 is injected into the inside, the bag body 9 is expanded by the injection pressure, and the outer peripheral surface is brought into close contact with the hole wall of the blasting hole 2 entirely. When this state is reached, the valve 13 of the injection hose 11 is closed to keep the bag 9 in close contact with the hole wall of the blast hole 2, and thereafter, the explosive 7 is blasted, as described above.
A crack is generated from both ends in the longitudinal direction in the cross-sectional shape of the blasting hole 2 having a long cross section in the longitudinally extending direction of the blasting hole 2.

FIG. 10 shows a modification of the bag 9, in which one rigid rod-shaped core material 12 is mounted on one side of the bag 9 over its entire length. A core material pipe 14 is inserted into the other side portion so as to correspond to the liquid inlet 9c. The pipe 14 is opened with its distal end close to the inner bottom surface of the bag body 9 and the base end is closed. It has a structure that is fixed in a protruding state from the rear end wall portion 9a of the body 9. The bag 9 having such a structure is suitable when the blasting hole 2 is formed in an upwardly inclined state.

That is, after the explosive 7 is loaded and fixed in the inner bottom portion (in the front end portion) of the bag body 9, the bag body 9 is inserted into the blast hole 2 inclined upward and then into the injection port 9c. When the liquid 10 is injected from the connected hose 11, the liquid 10 gradually flows into the bag 9.
As the liquid level rises from the rear end wall 9a side and fills the front end side, the air enclosed in the front end of the bag body 9 that reduces the blasting efficiency can be discharged to the outside through the pipe 14. . When the blast hole 2 is formed in a horizontal state, the pipe 14 is used for liquid injection, and the injection port 9c is used.
Can be used as a drain port.

FIG. 11 shows still another modification of the bag 9, in which a drain port 9d having a smaller diameter than a liquid inlet 9c provided in a rear end wall 9a of the bag 9 is connected to the front end of the bag 9. A core material pipe 15 is provided in the bag body 9 in correspondence with the liquid inlet 9c, and the opening at the front end and the base end thereof is opened from the front and rear wall surfaces of the bag body 9 respectively. It is made to protrude outside. Other structures are the same as in the above embodiment.

With this configuration, as shown in FIG. 7, the explosive 7 is loaded in the deep portion of the blasting hole 2 in a horizontal state, and after that, the bag 9 is inserted into the blasting hole 2 and then injected. When the liquid 10 is injected through the hose 11 from the liquid port 9c, the bag body 9 is expanded by the liquid 10 injected therein to bring its outer peripheral surface into close contact with the hole wall and a part of the liquid 10 has a small diameter drain port. From 9d, the liquid is discharged into the deep part of the blasting hole 2, and the liquid fills the part and the excess liquid is discharged to the outside through the core material pipe 15. Cross-sectional shape of the blasthole 2 above likewise sectional slot shape by blasting explosives 7 in this state
A crack is generated in the extending direction from both ends in the longitudinal direction in the shape .

[0028]

As described above, according to the first aspect of the present invention, an elongated hole having a long and narrow cross section is formed at a substantially central portion of a planned excavation surface of a crushed object such as a bedrock to a desired depth. In the longitudinal direction in the sectional shape of the bore hole
In the planned excavation plane on both sides orthogonal to each other, the length in the longitudinal direction of the cross-sectional shape of this borehole is taken as one side
This one side and other virtual
The borehole is placed in an equilateral triangle formed by the two sides.
Drilled to the desired depth being directed parallel to the longitudinal direction of the longitudinal sectional shape of a short section slot shape blasthole length to the longitudinal direction of the borehole cross-sectional shape in the cross-sectional shape than Le Further, in the planned excavation plane, blast holes having a long hole shape in cross section at positions at predetermined intervals outside from these blast holes at predetermined intervals and in the cross-sectional shape of adjacent blast holes. drilled to the desired depth in the longitudinal direction of the end portion while being opposed to each other, the upper and loaded explosive in each blasthole
Since the blasting holes near the borehole are sequentially blasted, the blasting holes having an oval cross section can be easily drilled compared to the conventional piercing work that forms a notch in the blasting hole having a circular cross section. Instead, the explosive charged in the blast hole is blasted so that the blasting force acts intensively in the short-side direction of the cross-sectional shape of the blast hole having an elliptical cross section, and in the longitudinal extension direction in the cross-sectional shape of the blast hole. Cracks can be surely generated.

Further, an elongated hole having an elongated cross section is formed to a desired depth substantially at the center of the planned excavation surface of the object to be crushed, and the length of the bore in the sectional shape of the bore is determined.
In the planned excavation plane on both sides perpendicular to the hand direction ,
The length in the longitudinal direction of the cross-sectional shape of the bore hole is defined as one side, and the one side and the other end extending outward from both ends of the one side.
In the planned excavation surface part of the equilateral triangle formed by the virtual two sides of
The blast hole with a short cross-sectional shape with a short length in the hand direction is defined as the longitudinal direction of the cross-sectional shape with respect to the longitudinal direction of the cross-sectional shape of the borehole.
Since it is drilled to the desired depth in a state where it is oriented parallel ,
By blasting these blast holes, cracks are intensively generated from both longitudinal ends in the cross-sectional shape of the blast holes to between the longitudinal ends in the cross-sectional shape of the bore hole facing the both ends. Therefore, the amount of explosive required to generate a crack from the blast hole toward the borehole can be reduced, and the crushed material surrounded by the blast hole, the crack and the borehole can be efficiently cored. It is.

In addition, blast holes having a long cross section are formed at predetermined intervals on both sides of the blast holes adjacent to the borehole at predetermined intervals on the planned excavation surface in the longitudinal direction in the cross-sectional shape of the adjacent blast holes. Since the parts are drilled to a desired depth in a state where they face each other, after blasting the blast holes close to the borehole, by sequentially blasting the outer blast holes, similarly between the ends of the adjacent blast holes as described above. Cracks can be intensively generated, and excavation and removal of the crushed object surrounded by the cracks by the inner void portion already excavated and removed can be easily performed.

According to the second aspect of the present invention, a blast hole having a long cross section and a small hole having a circular cross section are alternately formed along an outer peripheral edge of a planned excavation surface of a crushed object such as a bedrock. since the drilled to the desired depth in a state with its longitudinal <br/> direction in the cross-sectional shape of the blasthole of and a long hole shape at intervals in the circumferential direction of the outer periphery of the planned drilling plane, blasting blasthole When this is done, cracks can be intensively generated from the longitudinal end in the cross-sectional shape of the blast hole toward the small-diameter hole, and accurate excavation along the outer peripheral edge of the planned excavation surface becomes possible. In addition, the distance between adjacent blast holes can be increased because the adjacent blast holes are continuous through cracks through the intermediate holes, reducing the number of blast holes and the amount of explosives used. And the small diameter holes are circular, And rapidly performed, it is possible to perform efficiently the entire blasting construction of the tunnel.

Further, on the planned excavation surface surrounded by the row of blast holes, a row of blast holes having a long cross section is formed in the same arrangement as above with a predetermined interval inward from the row of blast holes. Since the blast hole array is blasted and the inner blast hole array is blasted beforehand, the object to be crushed within the planned excavation surface can be accurately and efficiently excavated.

[Brief description of the drawings]

FIG. 1 is a simplified front view showing an embodiment in which a borehole is provided in the center,

FIG. 2 is a simplified front view showing an embodiment in which holes are provided between blast holes,

FIG. 3 is a simplified plan view of a blast hole excavator having an elliptical cross section,

FIG. 4 is a simplified vertical sectional view showing a state in which explosives are inserted into a blast hole and sand is filled.

FIG. 5 is a simplified vertical sectional view showing a state in which a bag loaded with explosive is inserted into a blast hole;

FIG. 6 is a simplified longitudinal side view thereof,

FIG. 7 is a simplified longitudinal side view of a modified example thereof,

FIG. 8 is a simplified perspective view of a bag,

FIG. 9 is a simplified perspective view showing a state where the bag body is contracted.

FIG. 10 is a partially cut-away simplified perspective view showing another structure of the bag body.

FIG. 11 is a partially cut-away simplified perspective view showing still another structure of the bag body.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Crushed object 2 Blast hole 3 Bore hole 4 Vacancy 5, 6 slot 7 Explosive

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-49-7702 (JP, A) JP-A-56-52287 (JP, A) JP-A-53-105031 (JP, A) JP-A 55-52 26373 (JP, A) JP-A-59-141693 (JP, A) JP-A-57-98800 (JP, A) JP-A-60-69500 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) F42D 1/00-7/00

Claims (2)

(57) [Claims] 1. A long hole- shaped borehole having a thin and long cross section is formed at a substantially central portion of a planned excavation surface of a crushed object such as a bedrock to a desired depth .
Within the planned excavation plane on both sides perpendicular to the longitudinal direction, the longitudinal length in the cross-sectional shape of this borehole
From one side and both ends of this side to the outside
Inside the equilateral triangle formed by the other two virtual sides
Longer length in the cross-sectional shape than the above bore hole
Drilled to the desired depth being directed parallel to the longitudinal direction of the cross section to the longitudinal direction of the borehole cross-sectional shape of a short section slot shape blasthole the further the planned drilling plane
A certain distance outside these blast holes inside
Drilled to the desired depth sectional slot shape blasthole in a position in a state of being opposed to each other in the longitudinal direction of the end portion in the cross-sectional shape of the and adjacent blasthole at predetermined intervals, loading explosives in each blasthole And blasting sequentially from a blast hole near the borehole . 2. A blast hole having a long cross section and a small diameter hole having a circular cross section are alternately formed at predetermined intervals along an outer peripheral edge of a planned excavation surface of an object to be crushed such as a bedrock. The longitudinal direction in the cross-sectional shape of the hole is
Drilling to the desired depth in a state facing the circumferential direction, furthermore, at a certain interval inward from the hole row on the planned excavation surface surrounded by the hole row consisting of these blast holes and small diameter holes A blast hole having a cross-sectionally long hole shape is formed at predetermined intervals at predetermined intervals along the hole row to form a blast hole row, and thereafter, a hole composed of the blast hole and a small-diameter hole A blasting method characterized in that each blast hole in the row is charged and blasted, and then the inner blast row is blasted.