JP3253896B2 - Drilling machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drilling machine for drilling continuous slots (hereinafter referred to as "slits") in rock or concrete.

[0002]

2. Description of the Related Art Conventionally, for example, when a tunnel is excavated in a bedrock, slits having an appropriate depth are formed in the length direction of a planned tunnel in consideration of environmental problems and work safety, and are surrounded by these slits. It is being done to remove the damaged rock mass. As shown in FIG. 12, as a drilling machine for excavating such a slit, a long rod B having a drilling bit A at its tip and a short rod having a drilling bit B 'at its tip. The rod B ′ is a rod B, B in which the drill bit A of the long rod B is located forward of the drill bit A ′ of the short rod B ′, and is adjacent to the diameter of these drill bits A, A ′. A plurality of drilling machines have been known in which a plurality of drilling machines are arranged in parallel so that the distance between the centers of the '' s is reduced, and these rods B and B 'are simultaneously rotated and the slit is excavated by hitting the rear end side. ing.

[0003]

As described above, according to the conventional drilling machine, the drilling bits A and A 'of the adjacent long rod B and short rod B' are displaced from each other in the front-rear direction. Then, when all the long and short rods B and B 'are simultaneously rotated and the rear end face is perforated, the hole is drilled in the rock. First, the perforated bit A is projected by the other long rod B protruding forward. As shown in FIG. 13, circular holes H are drilled at regular intervals in advance, and then adjacent to the long rod B by the drill bit A ′ of the short bit B ′ following the long rod B, as shown in FIG. A circular hole H 'is to be drilled in the rock part between the circular holes H, H so that a part thereof overlaps the circular hole H, and the drill bit A of the long rod B and the short rod B' The area of the rock mass drilled by the drill bit A 'is significantly different. It will be.

That is, the drill bit A of the long rod B drills the entire cross section of the circular hole H having the same outer diameter.
The drill bit A 'of the short rod B' drills a rock portion with a small remaining area between the circular holes H, which cannot be drilled by the drill bit A of the long rod B. In addition, the rock part excavated by the drill bit A 'of the short rod B' has a rock strength by the impact and rotation of the drill bit A when the circular hole H is drilled first by the drill bit A of the long rod B. In the case of a rock mass originally having many cracks or a low strength rock mass, the long rod B, the drill bit A of the B,
The rock part between the circular holes excavated by A is almost in a crushed state.

For this reason, when excavating a slit with a drilling machine, a greater load (excavation resistance) is applied to the drilling bit A of the long rod B than to the drilling bit A 'of the short rod B'.
While the wear of the drill bit A becomes intense and the load on the long rod B and the rotating mechanism increases, the drill bit A 'of the short rod B' may be hit in an empty state. There is a problem that the durability of a rotation mechanism for simultaneously rotating the rod B 'is impaired.

The present invention has been made in view of such a problem, and an object of the present invention is to uniformly operate all the rods projecting a drill bit so that the drill bit of any of the rods can be used. It is an object of the present invention to provide a drilling machine capable of smoothly excavating a slit so as to exert the same drilling ability.

[0007]

According to a first aspect of the present invention, there is provided a drilling machine in which a plurality of rods each having a drill bit protruding at a tip thereof are arranged side by side. In a drilling machine configured to drill a slot by hitting while rotating a rod, a small-diameter drill bit and a large-diameter drill bit are provided at the tip of each of the rods. The small-diameter drill bits are aligned integrally on the plane perpendicular to the axis of the rod, while the adjacent large-diameter drill bits are alternately shifted in the front-rear direction. The hole drilled by the large-diameter drill bit is configured to partially overlap.

According to a second aspect of the present invention, a plurality of rods having a piercing bit protruding at the tip are arranged in parallel, and the rods are hit while rotating the rods so as to pierce the slots. In the drilling machine configured, a second rod having a first rod having a large-diameter drill bit protruding at the distal end, a small-diameter drill bit at the distal end, and a large-diameter drill bit integrally provided on the rear side of the small-diameter drill bit. The rod is aligned with the tip of the large-diameter drill bit of the first rod and the tip of the small-diameter drill bit of the second rod on a plane perpendicular to the axis of the rod, and the large-diameter drill bit of the first rod and the second rod are aligned. The holes drilled by the large-diameter drilling bits are alternately juxtaposed so as to overlap.

[0009]

According to the first aspect of the invention, all the small-diameter drill bits provided at the tips of the side-by-side rods have their tips aligned on a plane perpendicular to the axis of the rod. When excavating, the tips of all the small-diameter drill bits are in contact with the rock surface, and the rotating torque from the rotating mechanism and the impact force of the striking mechanism act uniformly, and the small-diameter drill bits cause the small-diameter holes to be simultaneously formed. Is excavated. The small-diameter holes formed by the small-diameter drill bits are excavated at small intervals in the direction parallel to the rods. The large-diameter hole is drilled while expanding the small-diameter hole by the large-diameter drill bit.

At this time, in the adjacent rods, the large-diameter drill bit of one rod is shifted in the front-rear direction with respect to the large-diameter drill bit of the other rod. The large-diameter drilling bit of the rod is used to expand the small-diameter hole already drilled by the small-diameter drilling bit at the tip of the rod into a large-diameter hole, and then by the large-diameter drilling bit of the other rod disposed on the rear side. The small-diameter hole drilled by the small-diameter drill bit at the tip of the rod is expanded in diameter, and a large-diameter hole overlapping the previously drilled large-diameter hole is drilled by the large-diameter drill bit of the one rod.

In this case, at the start of excavation of a large-diameter hole by a large-diameter drill bit, the large-diameter drill bit of one of the rods disposed on the front side starts excavation first.
Although the excavation resistance is larger than that of the other rod, only the small diameter hole already drilled by the tip small diameter drill bit of the rod is used as a guide to excavate the surrounding ground portion, so that the small diameter of the other rod is small. The drilling resistance is only slightly larger than the drilling resistance by the drilling bit, and the drilling of the other rod by the large-diameter drilling bit is performed immediately after the large-diameter drilling bit of the one rod. The load at the time of excavation by the diameter drilling bit hardly changes, and a predetermined slit through which all the large diameter holes communicate in series is smoothly excavated.

Next, according to the second aspect of the present invention, the large-diameter drill bit and the small-diameter drill bit provided at the distal ends of the first and second rods arranged side by side have the same protruding length from the rod distal end. Therefore, as in the invention according to the first aspect, when excavating the slit, the tip bits of all the rods are in contact with the rock surface, and the rotational torque from the rotating mechanism and the impact of the striking mechanism are reduced. The force acts almost uniformly and the first
When the large-diameter hole formed by the large-diameter drill bit of the rod and the small-diameter hole formed by the small-diameter drill bit of the second rod are simultaneously excavated with a small interval therebetween, and further excavated by these large- and small-diameter drill bits, The small-diameter hole drilled by the small-diameter drill bit becomes an enlarged large-diameter hole by the large-diameter drill bit of the second rod following the small-diameter drill bit, and the large-diameter hole is drilled by the large-diameter drill bit of the first rod. The slit is formed so as to partially overlap the large-diameter hole.

[0013] Even when the slit is excavated, the area excavated by the large-diameter drill bit of the first rod is
Since the area excavated by the small-diameter drill bit and the large-diameter drill bit of the second rod is equal, the load at the time of excavation applied to both rods hardly changes, and a predetermined slit in which all the large-diameter holes communicate in series is formed. Excavation can be performed smoothly and efficiently.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing the structure of a parallel bit according to the first embodiment of the present invention; FIG. A fixed-length steel rod 1A having a small-diameter drill bit 2 and a large-diameter drill bit 3A integrally provided at a front end thereof with a small gap in front and rear, and the same diameter as the small-diameter drill bit 2 at the front end. And a fixed-length steel rod 1B integrally provided with a small-diameter drill bit 2 having the same shape and a large-diameter drill bit 3B disposed so as to be connected to the rear side of the small-diameter drill bit 2. A plurality (four in the figure) of the rods 1A and 1B are alternately arranged at a constant interval slightly shorter than the diameter of the large diameter drilling bits 3A and 3B. It constitutes a parallel bit for slot excavation.

The configuration of the juxtaposed bits will be described in more detail. The lengths of all the rods 1A and 1B are the same, and the centers of the rods 1A and 1B are centered on the center lines of the rods 1A and 1B. The large and small diameter perforated bits 2, 3A and 2, 3B are integrally fixed to each other and
The projecting lengths from the tips of A and 1B to the tip of the drill bit 2 are all the same. That is, the lengths from the base ends of the rods 1A and 1B to the tip of the small-diameter drill bit 2 are formed to be the same,
Therefore, the tip of the small-diameter drill bit 2 juxtaposed is the rod 1A,
Guide shell aligned on a plane perpendicular to the axis of 1B
10 (shown in FIG. 5) is arranged so as to rotate and move back and forth in the axial direction.

Further, in adjacent rods 1A and 1B,
The rear end neck 2a of the small-diameter drill bit 2 disposed on one rod 1A is changed to the neck 2b of the small-diameter drill bit 2 of the other rod 1B.
Therefore, the large-diameter drill bit 3A provided on one rod 1A has a longer separation distance rearward from the small-diameter drill bit 2 than the large-diameter drill bit 3B of the other rod 1B. The large-diameter drill bit 3B of the other rod 1B is juxtaposed at a position facing the neck 2a of the small-diameter drill bit 2 having the long neck 2a. That is, the large-diameter drill bits 3A and 3B are alternately arranged in a staggered manner while being shifted in the front-rear direction.

Each of the small-diameter drill bits 2 has a larger diameter than the rods 1A and 1B. However, a certain interval is provided between the adjacent small-diameter drill bits 2 and 2 and a plurality of cutting bits are formed on the front end face thereof. The tip 4 projects radially from the center toward the outer peripheral end, and a concave arcuate cut is formed on the outer peripheral surface of the small-diameter drill bit 2 between the adjacent cutting tips 4 as shown in FIG. A powder discharge groove 5 is provided. On the other hand, in the drill bits 3A and 3B having a diameter larger than that of the small-diameter drill bit 2, a plurality of cutting tips 6 are radially protruded from the outer peripheral edge of the neck of the small-diameter drill bit 2 toward the outer peripheral end thereof. As shown in FIG. 4, the outer peripheral surface of the large-diameter drill bit 3A, 3B between the adjacent cutting tips 6, 6 is provided with a concave arc-shaped curved powder discharge groove 5 '.

A fluid supply hole 8 is formed in each of the rods 1A and 1B at the center thereof so as to communicate with a fluid ejection port 7 drilled from the base end face to the tip end face of the small diameter drill bit 2. Further, fluid ejection holes 9 and 10 are formed from the tip of the fluid supply hole 8 so as to communicate with the small-diameter drill bit 2 and the above-mentioned dust discharge grooves 5 and 6 of the large-diameter drill bits 3A and 3B.

The rods 1A and 1B having the large- and small-diameter perforated bits at the distal end configured as described above are disposed on the front half of the guide shell 10 in a state where they are aligned at regular intervals in the lateral direction as described above. The rods 1A and 1B are
As shown in, the front end portion of the front shell of the guide shell 10 is rotatably and axially slidably inserted into and supported by the front rod receiving member 11, while the base end is moved back and forth on the guide shell 10. A rear rod receiving member 13 fixed on a front end of a freely movable movable base plate 12 is rotatably and axially slidably inserted and supported.

As is well known, a rotary drive mechanism 14 for simultaneously rotating all the rods 1A and 1B and a rod 1
A striking mechanism 15 for striking the base ends of A and 1B is provided, and together with these rods 1A and 1B, constitutes a drilling machine. The movable base plate 12 is connected to an endless chain or a rotary screw rod provided in the guide shell 10, and is driven by a motor to drive the guide shell.
It is configured to move back and forth on the top 10. Further, a fixing tool 16 for fixing the guide shell 10 to the bedrock surface is protruded from the front end surface of the guide shell 10.

The guide shell 10 is mounted on a leading end of a boom 17 provided on a traveling vehicle (not shown) so as to be rotatable in up, down, left and right directions via a support member 18. The support member 18
The hydraulic jack 19 is connected to and supported by the boom 17 so as to be able to freely bend vertically.

In order to form a slit S for excavating a tunnel in the rocky ground by the drilling machine constructed as described above, the traveling vehicle is moved to a position near the face of the tunnel and the boom 17 is operated. After the shell 10 is opposed to the face to be drilled and the hydraulic jack 19 is driven to adjust the drilling angle to a predetermined angle, the movable base plate 12 is advanced to advance the tip of the small-diameter drill bit 2 of all the rods 1A and 1B. Is brought into contact with the perforation position on the face, and the fixing tool 16 is pressed against the face to fix the guide shell 10.

In this state, when the rods 1A and 1B are rotated and their rear ends are hit, the small diameter drill bits 2 of the rods 1A and 1B are uniformly pressed against the face, so that all the rods 1A and 1B are pressed. As shown in FIG. 6, a plurality of small-diameter holes H are excavated in the parallel direction of the rods 1A and 1B with a constant interval between the small-diameter drill bits 2 by applying uniform rotational torque and impact force to the rods. You.

When a small-diameter hole H having a constant depth is excavated by the small-diameter drill bit 2, one of the rods having the large-diameter drill bit 3 A at the rear of the small-diameter drill bit 2 having a long neck portion is then used.
The large-diameter drill bit 3B of the other rod 1B, which is disposed before the large-diameter drill bit 3A prior to 1A, reaches the small-diameter hole H drilled by the small-diameter drill bit 2 of the rod 1B. As shown in FIG. 7, a large-diameter hole H ′ obtained by expanding the small-diameter hole H is excavated while excavating the rock around the small-diameter hole H.

At this time, the excavation resistance caused by the large-diameter drill bit 3B acts on the rotating mechanism 14 via the rod 1B. However, when the small-diameter drill bit 2 excavates and rotates the small-diameter hole H, the surrounding rock is formed. Instead of excavating the rock part corresponding to the entire cross section of the large-diameter drill bit 3B, the surrounding ground obtained by subtracting the area of the small-diameter hole H from the excavation area by the large-diameter drill bit 3B is reduced. Since the part is excavated, the excavation resistance is small.Besides, the excavation by the large-diameter drill bit 3A of one rod 1A is started following the large-diameter drill bit 3B, so that all the rods 1A, 1B
In this state, the large-diameter drill bit 3A advances with the small-diameter hole H previously excavated by each small-diameter drill bit 2 as a guide, and as shown in FIG. A predetermined slit S in which a part of the outer peripheral portion of the large-diameter hole H ′ excavated by the large-diameter drilling bits 3A and 3B of 1A and 1B partially overlaps and all the large-diameter holes H ′ communicate in series. It will be excavated.

In this manner, the rods 1A and 1B advance into the bedrock by rotating and hitting the rods 1A and 1B, thereby allowing the rods 1A and 1B to enter the rock and excavating the slit S having a constant depth. During the excavation of the slit S,
Water or air is supplied to the fluid supply hole 8 provided at the center of each rod 1A, 1B from the rear side of the drilling machine, and the fluid ejection port 7 provided in the small-diameter drill bit 2 and the large-diameter drill bits 3A, 3B. And the jet holes 9 and 10 to jet into the slit S, and the cuttings excavated by the cutting tips 4 and 5 of the drill bit are discharged backward together with the fluid through the gap between the slit S and the rods 1A and 1B. When a slit S having a constant depth is excavated, the movable trolley 12 is retracted, the rods 1A and 1B are extracted from the slit S, and the excavation work of the next slit S is performed again in the same manner as described above.

FIG. 9 shows the structure of a juxtaposed bit according to the second aspect of the present invention, wherein a first rod 21A made of steel having a fixed length and having a large diameter drill bit 3A integrally provided at the tip end. A plurality of steel second rods 21B having a small-diameter drill bit 2 at the front end and a large-diameter drill bit 3B integrally provided at the rear end of the small-diameter drill bit 2 are shown in FIG. Book), first and second rods 21A, 21 alternately and adjacently
The distance between the centers of B 1 is juxtaposed at a fixed interval slightly shorter than the diameter of the large-diameter perforated bits 3A and 3B.

The first rod 21A and the second rod 21B have the same length, and the large-diameter drill bit 3A is disposed on the same rod at the tip of the first rod 21A and is integrally fixed thereto. A large-diameter drill bit 3B of the same diameter and the same shape as the large-diameter drill bit 3A is provided at the tip of the second rod 21B, and a small-diameter drill bit 2 is provided at the center of the front end face of the large-diameter drill bit 3B on the same center line as the rod. And are fixed together.
Similarly to the above embodiment of the present invention, the tip of the drill bit on the tip side, that is, the tip of the large-diameter drill bit 3A of the first rod 21A and the tip of the small-diameter drill bit 2 of the second rod 21B are rod-shaped. Are arranged on the guide shell 10 so as to be rotatable and movable back and forth in the axial direction in a state of being aligned on a plane perpendicular to the axis.

The shape and structure of the small-diameter drill bit 2 and the large-diameter drill bits 3A and 3B, and the drilling machine together with the rotating mechanism 14 and the striking mechanism 15 installed on the movable base plate 12 on the guide shell 10 constitute a drilling machine. Since the same structure is the same as that of the first embodiment of the present invention, the same portions are denoted by the same reference numerals and the description thereof will be omitted.

With this configuration, the first rod 21A
When the leading end surfaces of the large diameter drilling bit 3A and the small diameter drilling bit 2 of the second rod 21B are brought into contact with the drilling position of the face face, these rods are rotated and the rear ends are hit. Since the tip bit of the rod is in contact with the face, a uniform rotational torque and a striking force act on the first rod 21A and the first rod 21A, and the large-diameter drill bit 3A of the first rod 21A is used as shown in FIG. As shown in the large hole H ',
The small-diameter holes H are simultaneously excavated at a fixed interval from each other by the small-diameter drill bit 2 of the second rod 21B.

Further, the first rod 21A and the second rod 21B
When the large-diameter hole H 'and the small-diameter hole H are excavated while pushing the small-diameter hole H, the large-diameter drill bit 3B of the second rod 21B following the small-diameter drill bit 2 for excavating the small-diameter hole H becomes larger. The ground around the small-diameter hole H drilled is excavated to make the small-diameter hole H a large-diameter hole H ′.

At this time, the large-diameter drill bit of the first rod 21A
Since the area of the rock excavated by 3A and the area of the rock excavated by the small-diameter drill bit 2 and the large-diameter drill bit 3B of the second rod 21B are substantially equal, all the rods 21A, 21
The load due to the excavation resistance on B becomes substantially equal, and the large-diameter hole H ′ excavated by the large-diameter drill bit 3A of the first rod 21A is excavated by the large-diameter drill bit 3B of the second rod 21B. A part of the outer peripheral portion of the large-diameter hole H ′ overlaps with that of FIG.
As shown in the figure, a predetermined slit S in which all the large-diameter holes H 'communicate in series is excavated.

[0033]

As described above, according to the drilling machine according to the first aspect of the present invention, a small-diameter drill bit and a large-diameter drill bit are provided at the tips of the rods arranged at regular intervals as drill bits. The large-diameter drill bit is positioned integrally on the rear side of the small-diameter drill bit, and the ends of these small-diameter drill bits are aligned on a plane perpendicular to the axis of the rod, while adjacent large-diameter drill bits are sequentially placed. The holes drilled by these large-diameter drill bits are alternately shifted in the front-rear direction so that part of the holes drilled by these large-diameter drill bits are overlapped. In this manner, the rotating torque from the rotating mechanism and the striking force of the striking mechanism can be uniformly applied to each rod, and these small-diameter drill bits can simultaneously drill small-diameter holes. Perforated In addition to the wear of the rods, the load on the rods and the rotating mechanism is reduced, and not only the durability is improved, but also the excavation of all rods can be done smoothly by reducing the energy loss of impact and rotation. it can.

Further, the small-diameter holes drilled by the small-diameter drill bits of each rod precede the small-diameter holes, and the small-diameter holes are used as guides to accurately follow the large-diameter drill bits of each rod. Can be excavated to expand into a large-diameter hole, and a part of the adjacent large-diameter hole overlaps to excavate a slit in which the large-diameter hole is continuous.

At this time, since the rock area around the small diameter hole drilled by the large diameter drill bit of each lot is substantially equal,
Even during excavation with these large-diameter drill bits, the excavation resistance is substantially uniform, and the rotating torque and impact force can be applied to each rod while being evenly distributed, so that the drilling operation can be performed accurately and efficiently. is there.

According to the second aspect of the present invention, the first rod having the large-diameter drill bit protruding at the distal end, the small-diameter drill bit at the distal end, and integrally provided on the rear end side of the small-diameter drill bit. And a second rod having a large diameter drill bit.
The tip of the large-diameter drill bit of the rod and the tip of the small-diameter drill bit of the second rod are aligned on a plane perpendicular to the axis of the rod, and the large-diameter drill bit of the first rod and the large-diameter drill bit of the second rod are aligned. , The large-diameter drill bit and the small-diameter drill bit provided at the ends of the side-by-side first and second rods respectively are formed in the rock. In contact with the surface, the rotating torque from the rotating mechanism and the striking force of the striking mechanism can be applied substantially uniformly to each rod. Therefore, the striking and rotating of all the rods can be performed in the same manner as in the first aspect. Energy loss can be reduced and the slit can be dug smoothly.

Further, a large-diameter hole formed by expanding the small-diameter hole is excavated by using the small-diameter hole drilled by the small-diameter drill bit at the leading end of the second rod, which is preceded by the large-diameter drill bit of the second rod, as a guide. The slit can be accurately excavated while overlapping the large-diameter hole with the large-diameter hole excavated by the large-diameter drill bit of the first rod.

Even when the slit is formed by excavation, the area excavated by the large-diameter drill bit of the first rod is:
Since the area excavated by the small-diameter drill bit and the large-diameter drill bit of the second rod is equal, the load at the time of excavation applied to both rods hardly changes, and a predetermined slit in which all the large-diameter holes communicate in series is formed. It can excavate smoothly and efficiently. The juxtaposed drill bit according to the present invention is not limited to rock as described above, but can be used for drilling slits in concrete.

[Brief description of the drawings]

FIG. 1 is a simplified plan view of a drilling machine,

FIG. 2 is an enlarged plan view of a tip portion of the juxtaposed rod,

FIG. 3 is a front view of a small-diameter drill bit;

FIG. 4 is a vertical sectional front view of a large-diameter drill bit;

FIG. 5 is a simplified side view showing a state in which a slit is perforated;

FIG. 6 is a plan view of a small-diameter hole drilled by a small-diameter drill bit;

FIG. 7 is a plan view showing a state where a small-diameter hole is enlarged by a large-diameter drill bit of one rod;

FIG. 8 is a plan view in the case where a large-diameter hole is continuously formed as a slit,

FIG. 9 is an enlarged plan view showing the structure of another juxtaposed drill bit according to the present invention;

FIG. 10 is a plan view of a hole drilled by a bit on the tip side,

FIG. 11 is a plan view when a large diameter hole is continuously formed as a slit,

FIG. 12 is a simplified plan view of a conventional drilling machine,

FIG. 13 is a plan view of a hole drilled by a drill bit of a long rod of the drilling machine.

FIG. 14 is a plan view of a slit excavated with a long and short rod drill bit.

[Explanation of symbols]

 1A, 1B rod 2 Small diameter drill bit 3A, 3B Large diameter drill bit 4, 6 Cutting tip 21A First rod 21B Second rod

Continuation of front page (72) Inventor Keisuke Yasui 2-2-2 Matsuzakicho, Abeno-ku, Osaka-shi Okumura Gumi Co., Ltd. (56) References JP-A-54-139801 (JP, A) JP-A-3-140591 ( JP, A) JP-A-7-301085 (JP, A) JP-A-8-42279 (JP, A) JP-A-61-80891 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , (DB name) E21B 6/02

Claims (2)

(57) [Claims] 1. A drilling machine in which a plurality of rods each having a drill bit protruding at a tip end are arranged in parallel, and a slot is drilled by hitting while rotating these rods. A small-diameter drill bit and a large-diameter drill bit are provided integrally with the large-diameter drill bit located at the rear side of the small-diameter drill bit at the tip of the rod, and the tips of these small-diameter drill bits are perpendicular to the axis of the rod. While arranged on the upper side, adjacent large-diameter drill bits are sequentially shifted alternately in the front-rear direction so as to partially overlap holes drilled by these large-diameter drill bits. Drilling machine. 2. A piercing machine in which a plurality of rods having a piercing bit protruding at the distal end are arranged side by side and a slot is pierced by hitting while rotating these rods. A first rod having a large-diameter drill bit protruding therefrom, and a second rod having a small-diameter drill bit at the tip and a large-diameter drill bit integrally provided on the rear side of the small-diameter drill bit. The tip of the large-diameter drill bit and the tip of the small-diameter drill bit of the second rod are aligned on a plane perpendicular to the axis of the rod, and excavation is performed by the large-diameter drill bit of the first rod and the large-diameter drill bit of the second rod. A drilling machine characterized in that holes to be drilled are alternately arranged side by side so as to overlap.