Double pipe hole drilling device and hole drilling method using the double pipe hole drilling device

Abstract

To propose a double-pipe drilling device capable of suppressing labor and time required for replenishment work of an inner rod and an outer casing, and a drilling method using the device.SOLUTION: In a double-pipe drilling device 1, a down-the-hole hammer 3 has a hammer body portion 3a positioned radially inside an outer casing 4, and an enlarged diameter portion 3c projecting radially outward from the hammer body portion 3a in front of the outer casing 4. A rear end connecting portion 2a of an inner rod 2 is located forward of a rear end connecting portion 4a of the outer casing 4 when connected to a drive mechanism 5. An axial distance L1 from the outer casing 4 to the enlarged diameter portion 3c is set longer than an axial distance L2 from the rear end connecting portion 4a of the outer casing 4 to the rear end connecting portion 2a of the inner rod 2 when connected to the drive mechanism 5.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a double-tube drilling device including an inner rod having a down-the-hole hammer at its front end and an outer casing into which the inner rod is inserted, and a drilling method using this double-tube drilling device.

Background Art

[0002] In performing civil engineering work such as foundation anti-seismic work and small well work, in order to excavate easily collapsible ground, a double-tube drilling device including an inner rod having a down-the-hole hammer at its front end and an outer casing into which the inner rod is inserted is used (see, for example, Patent Document 1). When the drive mechanism provided in this type of double-tube drilling device is operated, a striking force is generated from the down-the-hole hammer attached to the inner rod, so that the ground can be excavated by the bit provided on the down-the-hole hammer. Further, by advancing the outer casing as the excavation by the down-the-hole hammer progresses, it is possible to prevent the collapse of the drilled hole.

[0003] Also, in such a double-tube drilling device, there is known one in which an enlarged diameter portion having a diameter equal to or larger than that of the outer casing is provided on the down-the-hole hammer. When using a down-the-hole hammer having such an enlarged diameter portion, since the ground is excavated with a hole diameter equal to or larger than the outer diameter of the outer casing, the load on the outer casing can be suppressed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, when the depth of the hole drilling exceeds the length of the inner rod or the outer casing, after drilling to a predetermined depth, the drive mechanism attached to the rear end portions of the inner rod and the outer casing is temporarily separated, and a new inner rod and an outer casing are added to the original inner rod and the outer casing, and an operation of attaching the drive mechanism to the new inner rod and the outer casing is performed. Here, in order to attach the front end portion of the new inner rod to the rear end portion of the original inner rod when adding the new inner rod to the original inner rod, the original inner rod must be restrained. Therefore, it is necessary to temporarily retract the original inner rod to expose its rear end portion from the outer casing. That is, when using a down-the-hole hammer having an expanded diameter portion, the expanded diameter portion must be temporarily reduced in diameter and then the original inner rod must be retracted, which requires time and effort for reducing the diameter of the expanded diameter portion and causes a decrease in workability.

[0006] In view of such conventional problems, an object of the present invention is to propose a double-tube hole drilling device capable of suppressing the time and effort required for the operation of adding the inner rod and the outer casing. At the same time, a hole drilling method using this double-tube hole drilling device is also proposed.

Means for Solving the Problems

[0007] The present invention provides a double-tube drilling device comprising an inner rod equipped with a downhole hammer at its front end and an outer casing into which the inner rod is inserted. The rear-end connecting portion of the inner rod and the rear-end connecting portion of the outer casing are connected to a drive mechanism for drilling. In a state separated from the drive mechanism, a new inner rod and a new outer casing can be added to the rear-end connecting portion of the inner rod and the rear-end connecting portion of the outer casing. The downhole hammer has a hammer body portion positioned radially inside the outer casing and an expanded diameter portion protruding radially outward from the hammer body portion in front of the outer casing. In a state connected to the drive mechanism, the rear-end connecting portion of the inner rod is positioned in front of the rear-end connecting portion of the outer casing, and the axial distance from the outer casing to the expanded diameter portion is set longer than the axial distance from the rear-end connecting portion of the outer casing to the rear-end connecting portion of the inner rod in a state connected to the drive mechanism.

[0008] In such a double-tube drilling device, it is preferable that the outer casing has a ring bit protruding radially inward from the inner peripheral surface of the outer casing and approaching the outer peripheral surface of the hammer body portion.

[0009] Also, in this double-tube drilling device, it is preferable that the inner rod has a protruding portion protruding radially outward and approaching the inner peripheral surface of the outer casing.

[0010] Also, in this double-tube drilling device, it is preferable that the hammer body portion has a sludge discharge passage communicating with the gap between the inner rod and the outer casing and opening in front of the outer casing.

[0011] The present invention also relates to a drilling method using a double-tube drilling device. The double-tube drilling device includes an inner rod having a down-the-hole hammer at its front end and an outer casing into which the inner rod is inserted. The rear-end connecting portion of the inner rod and the rear-end connecting portion of the outer casing are connected to a drive mechanism for drilling. In a state separated from the drive mechanism, a new inner rod and a new outer casing can be added to the rear-end connecting portion of the inner rod and the rear-end connecting portion of the outer casing. The down-the-hole hammer has a hammer body portion located inside the outer casing in the radial direction and a diameter-expanding portion protruding radially outward from the hammer body portion in front of the outer casing. In a state connected to the drive mechanism, the rear-end connecting portion of the inner rod is located in front of the rear-end connecting portion of the outer casing. The axial distance from the outer casing to the diameter-expanding portion is set to be longer than the axial distance from the rear-end connecting portion of the outer casing to the rear-end connecting portion of the inner rod in a state connected to the drive mechanism. After operating the drive mechanism to excavate the ground with the down-the-hole hammer and advancing the inner rod and the outer casing in an oblique direction or a horizontal direction for drilling, when adding the new inner rod and the new outer casing, the steps include separating the drive mechanism from the rear-end connecting portion of the outer casing; retracting the inner rod with the diameter-expanding portion in an expanded state to expose the rear-end connecting portion of the inner rod from the rear-end connecting portion of the outer casing; adding a new inner rod to the rear-end connecting portion of the inner rod and adding a new outer casing to the rear-end connecting portion of the outer casing; connecting the new inner rod to the drive mechanism and advancing the new inner rod, and then connecting the new outer casing to the drive mechanism.

Advantages of the Invention

[0012] According to the double-tube hole-drilling device of the present invention having the above-described configuration, since the axial distance from the outer casing to the diameter-expanding portion is set to be longer than the axial distance from the rear-end connecting portion of the outer casing to the rear-end connecting portion of the inner rod in a state of being connected to the drive mechanism, even without reducing the diameter of the diameter-expanding portion, the original inner rod can be retracted to expose the rear-end connecting portion thereof from the rear-end connecting portion of the outer casing, and a new inner rod can be added. That is, when adding the inner rod and the outer casing, since it is not necessary to reduce the diameter of the diameter-expanding portion, the labor and time required for the work can be suppressed.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0014] Hereinafter, with reference to the drawings, an embodiment of a double-tube hole-drilling device according to the present invention and a hole-drilling method using this double-tube hole-drilling device will be described. Note that the excavation by the illustrated double-tube hole-drilling device shows the case of providing a horizontal hole in the ground. In addition, the front-rear direction in the following description is the direction along the illustrated axis C, where "front" is the back side when drilling the hole, and "rear" is the entrance side when drilling the hole.

[0015] FIG. 1 is a diagram schematically showing an embodiment of a double-tube hole-drilling device according to the present invention, and FIG. 2 is a partially enlarged view of the double-tube hole-drilling device shown in FIG. 1. The double-tube hole-drilling device 1 of the present embodiment includes an inner rod 2, a down-the-hole hammer 3, an outer casing 4, and a drive mechanism 5.

[0016] The inner rod 2 is a long member as shown in the figure, and is hollow in this embodiment. A down-the-hole hammer 3 is attached to the front end of the inner rod 2. Further, at the rear end of the inner rod 2, an inner rod rear end connecting portion 2a formed in a male screw shape is provided in this embodiment.

[0017] As shown in FIG. 2, a protruding portion 2b protruding radially outward is provided on the outer peripheral surface of the inner rod 2. The protruding portion 2b of this embodiment is plate-shaped, and a plurality of them are provided at intervals in the circumferential direction with respect to the outer peripheral surface of the inner rod 2.

[0018] The down-the-hole hammer 3 includes a hammer main body portion 3a connected to the front end of the inner rod 2, and a pilot bit 3b provided at the front end of the hammer main body portion 3a and having a plurality of tips on the front side portion. Further, on the front outer peripheral surface of the hammer main body portion 3a, an enlarged diameter bit 3c protruding radially outward from the hammer main body portion 3a and having a plurality of tips on the front side portion is provided. The enlarged diameter bit 3c corresponds to the "enlarged diameter portion" in this specification and the like. The enlarged diameter bit 3c can be switched between an enlarged diameter state protruding radially outward from the outer peripheral surface of the illustrated hammer main body portion 3a and a reduced diameter state aligned with the outer peripheral surface of the hammer main body portion 3a (or entering inside the outer peripheral surface of the hammer main body portion 3a). There is no limitation on the means for switching the enlarged diameter bit 3c between the enlarged diameter state and the reduced diameter state. For example, a mechanism using hydraulic pressure may be adopted, or a mechanism that switches according to the rotation direction of the down-the-hole hammer 3 may be adopted.

[0019] The hammer main body portion 3a includes a piston (not shown) inside thereof. This piston moves back and forth by an operating fluid (for example, air, water) supplied from the drive mechanism 5 into the internal space of the hollow inner rod 2, and generates an impact force at that time. The impact force generated by the piston is transmitted to the pilot bit 3b and the enlarged diameter bit 3c.

[0020] Further, the hammer main body portion 3a is provided with a groove portion 3d that recesses its outer peripheral surface and extends in the front-rear direction.

[0021] The outer casing 4 is hollow, and the inner rod 2 is inserted inside it. As shown in the figure, a gap S is provided between the outer casing 4 and the inner rod 2. The radially outer edge of the protrusion 2b described above is close to the inner peripheral surface of the outer casing 4 as shown in FIG. 2. Further, as shown in FIG. 1, a female-threaded outer casing rear-end connecting portion 4a is provided at the rear end of the outer casing 4 in the present embodiment.

[0022] Also, the outer casing 4 is provided with a ring bit 4b having a plurality of tips at its front end. The inner peripheral surface of the ring bit 4b in the present embodiment protrudes radially inward from the inner peripheral surface of the outer casing 4.

[0023] The drive mechanism 5 includes a swivel joint 6 in the present embodiment. The swivel joint 6 includes a master coupling 6a provided with a male-threaded portion at its front end, and an extension rod 6b provided in front of the master coupling 6a and having a female-threaded portion at its front end. The female-threaded portion of the extension rod 6b can be screwed into the male-threaded inner rod rear-end connecting portion 2a. Also, the male-threaded portion of the master coupling 6a can be screwed into the female-threaded outer casing rear-end connecting portion 4a.

[0024] The drive mechanism 5 also has a function of supplying the above-described working fluid to the swivel joint 6. Here, the swivel joint 6 communicates with the hollow inner rod 2 in a state where the inner rod rear-end connecting portion 2a and the extension rod 6b are connected. By feeding the working fluid from the drive mechanism 5, the piston provided in the hammer main body portion 3a is actuated via the swivel joint 6 and the inner rod 2, and an impact force is applied to the pilot bit 3b and the expanded-diameter bit 3c.

[0025] Also, the swivel joint 6 is provided with a discharge port (not shown) that communicates with the gap S between the outer casing 4 and the inner rod 2 in a state where the rear end connecting portion 4a of the outer casing and the master coupling 6a are connected. As will be described later, the gap S is a space through which the slime (a mixture of excavated earth and sand, gravel, and water used during excavation) flows when drilling is performed by the double pipe drilling device 1, and the slime that has flowed through the gap S is discharged to the outside of the double pipe drilling device 1 from the discharge port.

[0026] Incidentally, as shown in the drawing, in a state where the rear end connecting portion 2a of the inner rod and the extension rod 6b are connected and the rear end connecting portion 4a of the outer casing and the master coupling 6a are connected, the hammer main body portion 3a is located at a position overlapping the ring bit 4b in the front-rear direction. Also, in this state, the outer peripheral surface of the hammer main body portion 3a is close to the inner peripheral surface of the ring bit 4b. And in this state, the rear side portion of the groove portion 3d communicates with the gap S, and the front side portion of the groove portion 3d is located in front of the ring bit 4b. Incidentally, the space formed inside the groove portion 3d corresponds to the "mud discharge passage" in this specification and the like.

[0027] Also, in a state where the rear end connecting portion 2a of the inner rod and the extension rod 6b are connected and the rear end connecting portion 4a of the outer casing and the master coupling 6a are connected, the distance L1 in the direction along the axis C from the ring bit 4b to the expanded diameter bit 3c is set to be longer than the distance L2 in the direction along the axis C from the rear end connecting portion 4a of the outer casing to the rear end connecting portion 2a of the inner rod.

[0028] And although not shown in the drawing, the drive mechanism 5 is provided with a boring machine that is connected to the swivel joint 6 via a shank rod. When the boring machine is driven, both the inner rod 2 and the outer casing 4 that are connected to the swivel joint 6 vibrate in the direction along the axis C and also rotate about the axis C. Also, by the boring machine, the inner rod 2 and the outer casing 4 can be advanced or retracted.

[0029] Next, a method of drilling the ground with the double pipe drilling device 1 configured as described above will be described with reference to FIGS. 3 and 4. Note that the double pipe drilling device 1 of the present embodiment can be used not only for drilling in the vertical direction with respect to the ground, but is particularly suitable for use in drilling in an oblique direction or horizontal drilling described below.

[0030] FIG. 3(a) shows a state in which excavation of the ground G is started and horizontal drilling is being performed. When performing horizontal drilling, as shown in FIG. 1, a down-the-hole hammer 3 is attached to the front end of the inner rod 2, the inner rod rear end connecting portion 2a and the extension rod 6b are connected, and the outer casing rear end connecting portion 4a and the master coupling 6a are connected. Then, when the drive mechanism 5 is operated, a striking force is generated from the piston provided in the hammer main body portion 3a by the working fluid supplied from the drive mechanism 5, and thereby the striking force is applied to the pilot bit 3b and the reaming bit 3c. Further, the inner rod 2 and the outer casing 4 connected to the swivel joint 6 both vibrate in the direction along the axis C and rotate about the axis C. Then, by advancing the inner rod 2 and the outer casing 4 in the horizontal direction in this state, horizontal drilling can be performed as shown in FIG. 3(a).

[0031] By the way, when drilling holes in the ground G in the horizontal or diagonal directions, due to the influence of gravity, the hole wall is more likely to collapse compared to drilling in the vertical direction. As shown in FIG. 1, when the under-reaming bit 3c of this embodiment drills a hole, for reasons described later, it is separated from the ring bit 4b provided at the front end of the outer casing 4 by a distance L1 in the direction along the axis C. Therefore, when the ground G to be drilled is a collapsible mountain, the hole wall drilled in advance by the under-reaming bit 3c collapses before the outer casing 4 reaches, and gravel or the like may accumulate between the under-reaming bit 3c and the outer casing 4. That is, the accumulated gravel or the like hinders the advancement of the outer casing 4, leading to a decrease in the drilling efficiency. On the other hand, the double-tube drilling device 1 of this embodiment is provided with a ring bit 4b at the front end of the outer casing 4, and the ring bit 4b vibrates in the direction along the axis C together with the outer casing 4 and also rotates around the axis C. Therefore, even if gravel or the like accumulates in front of the outer casing 4, the drilling efficiency can be maintained.

[0032] Also, although the down-the-hole hammer 3 has a relatively small diameter and is lightweight compared to the conventional down-the-hole hammer mainly for drilling in the vertical direction, as shown in the figure, it protrudes relatively long forward from the outer casing 4. Therefore, when drilling in the horizontal or diagonal directions, it is likely to tilt downward due to gravity. And if the down-the-hole hammer 3 drills in a tilted state downward, the drilling direction will be tilted more than the intended direction. For this reason, in this embodiment, as shown in FIG. 2, the inner peripheral surface of the ring bit 4b is made to protrude radially inward from the inner peripheral surface of the outer casing 4, so that the inner peripheral surface of the ring bit 4b is brought close to the outer peripheral surface of the hammer main body 3a. That is, the down-the-hole hammer 3 that tends to tilt downward due to gravity when drilling in the horizontal or diagonal directions can be supported by the ring bit 4b to suppress the tilt, so that the hole can be drilled in the intended direction.

[0033] Furthermore, as shown in Fig. 2, the inner rod 2 of the present embodiment is provided with a protrusion 2b, and the radially outer edge of the protrusion 2b is close to the inner peripheral surface of the outer casing 4. That is, the inclination of the down-the-hole hammer 3 during horizontal or diagonal hole drilling can be suppressed by the protrusion 2b being supported by the outer casing 4. Therefore, by supporting the hammer main body 3a by the ring bit 4b and supporting the protrusion 2b by the outer casing 4, hole drilling in the intended direction can be performed more reliably.

[0034] As described above, since the ring bit 4b of the present embodiment is close to the hammer main body 3a, it is difficult for the slime generated during hole drilling to pass between the hammer main body 3a and the ring bit 4b when discharging the slime. However, the front part of the groove 3d is located in front of the ring bit 4b, and the rear part of the groove 3d communicates with the gap S between the outer casing 4 and the inner rod 2. Therefore, the slime passes from the front part of the groove 3d through the inside of this groove 3d (mud discharge passage) to reach the gap S, and further flows through the gap S and is discharged to the outside of the double-tube hole drilling device 1 from a discharge port (not shown) provided in the swivel joint 6. Although the above-described protrusion 2b (see Fig. 2) is provided on the outer peripheral surface of the inner rod 2, since the protrusion 2b is provided at intervals in the circumferential direction with respect to the outer peripheral surface of the inner rod 2, the gap S is not blocked. Therefore, the flow of the slime is not impaired by the protrusion 2b.

[0035] When hole drilling is performed to a predetermined depth and it becomes necessary to add the inner rod 2 or the outer casing 4, the operation of the drive mechanism 5 is temporarily stopped. The expanding bit 3c may remain in the expanded state. Then, with the outer casing 4 fixed, the swivel joint 6 is rotated to release the screwing engagement between the rear end connecting portion 4a of the outer casing and the master coupling 6a. As a result, as shown in Fig. 3(b), the outer casing 4 and the swivel joint 6 can be separated.

[0036] Next, as shown in FIG. 3(c), the swivel joint 6 is retracted until the expanded-diameter bit 3c in the expanded-diameter state is caught by the ring bit 4b. As described above, the distance L1 in the direction along the axis C from the ring bit 4b to the expanded-diameter bit 3c in the state of FIG. 1 is set to be longer than the distance L2 in the direction along the axis C from the outer casing rear-end connecting portion 4a to the inner rod rear-end connecting portion 2a. Therefore, when the swivel joint 6 is retracted to the state of FIG. 3(c), the inner rod rear-end connecting portion 2a is exposed from the outer casing 4. Therefore, with the inner rod 2 fixed, the swivel joint 6 is rotated to disengage the screw engagement between the inner rod rear-end connecting portion 2a and the extension rod 6b, and the inner rod 2 and the swivel joint 6 can be separated.

[0037] After that, as shown in FIG. 4(a), an operation of adding a new inner rod 12 to the original inner rod 2 is performed. The new inner rod 12 in the present embodiment is provided with an inner rod front-end connecting portion 12a formed in a female screw shape, and the inner rod front-end connecting portion 12a can be screwed into the inner rod rear-end connecting portion 2a formed in a male screw shape. Therefore, by rotating the new inner rod 12 with the original inner rod 2 fixed, the new inner rod 12 can be added to the original inner rod 2.

[0038] After that, as shown in FIG. 4(a), an operation of adding a new outer casing 14 to the original outer casing 4 is performed. The new outer casing 14 in the present embodiment is provided with an outer casing front-end connecting portion 14a formed in a male screw shape, and the outer casing front-end connecting portion 14a can be screwed into the outer casing rear-end connecting portion 4a formed in a female screw shape. Therefore, by rotating the new outer casing 14 with the original outer casing 4 fixed, the new outer casing 14 can be added to the original outer casing 4.

[0039] The above-mentioned new inner rod 12 is provided with a male-threaded inner rod rear-end connecting portion 12b having the same shape as the inner rod rear-end connecting portion 2a. The new outer casing 14 is provided with a female-threaded outer casing rear-end connecting portion 14b having the same shape as the outer casing rear-end connecting portion 4a. Also, the new inner rod 12 and the outer casing 14 are substantially the same length. When the new inner rod 12 and the outer casing 14 are added to the original inner rod 2 and the outer casing 4, the inner rod rear-end connecting portion 12b is exposed from the outer casing rear-end connecting portion 14b.

[0040] Next, as shown in Fig. 4(b), with the new inner rod 12 fixed, the swivel joint 6 is rotated, and the inner rod rear-end connecting portion 12b and the extension rod 6b are screwed together to connect the two.

[0041] After that, when the swivel joint 6 is advanced, the original inner rod 2 also advances together with the new inner rod 12 connected to the swivel joint 6. Also, by advancing the swivel joint 6, the master coupling 6a approaches the outer casing rear-end connecting portion 14b. Therefore, with the new outer casing 14 fixed, the swivel joint 6 is rotated to screw the outer casing rear-end connecting portion 14b and the master coupling 6a together to connect the two.

[0042] After that, by operating the drive mechanism 5 again, drilling can be advanced deeper using the added new inner rod 12 and outer casing 14.

[0043] Thus, according to the double-tube drilling device 1 of this embodiment, the operation of adding the new inner rod 12 and the outer casing 14 can be performed while keeping the expansion bit 3c in the expanded state. Therefore, the labor and time required to reduce the diameter of the expansion bit 3c can be saved, and the addition operation can be performed efficiently.

[0044] As described above, although one embodiment of the present invention has been explained, the present invention is not limited to such a specific embodiment, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims, unless otherwise particularly limited in the above description. Also, the effects in the above embodiments are merely examples of the effects resulting from the present invention, and it does not mean that the effects of the present invention are limited to the above effects.

[0045] For example, in the above-described embodiment, the inner rod rear end connecting portion 2a was male-threaded and the outer casing rear end connecting portion 4a was female-threaded. However, the inner rod rear end connecting portion 2a may be female-threaded, and the outer casing rear end connecting portion 4a may be male-threaded. When using a female-threaded inner rod rear end connecting portion 2a, the extension rod 6b may be male-threaded, and when using a male-threaded outer casing rear end connecting portion 4a, the master coupling 6a may be female-threaded.

[0046] Also, the structures for connecting the inner rod rear end connecting portion 2a and the extension rod 6b, and the outer casing rear end connecting portion 4a and the master coupling 6a are not limited to those by the above-described threads. For example, a structure in which a protrusion provided on one side is inserted into a hole provided on the other side for connection may also be used.

Explanation of Reference Numerals

[0047] 1: Double-tube hole-drilling device 2: Inner rod 2a: Inner rod rear end connecting portion 2b: Protrusion 3: Down-the-hole hammer 3a: Hammer main body portion 3b: Pilot bit 3c: Diameter-expanding bit (diameter-expanding portion) 3d: Groove portion 4: Outer casing 4a: Outer casing rear end connecting portion 4b: Ring bit 5: Driving mechanism 6: Swivel joint 6a: Master coupling 6b: Extension rod 12: New inner rod 12a: Inner rod front-end connecting part 12b: Inner rod rear-end connecting part 14: New outer casing 14a: Outer casing front-end connecting part 14b: Outer casing rear-end connecting part G: Ground S: Gap

Claims

1. An inner rod having a downhole hammer at its front end, and an outer casing into which the inner rod is inserted. The rear end connecting portion of the inner rod and the rear end connecting portion of the outer casing are connected to a drive mechanism to perform hole drilling. In a state separated from the drive mechanism, a new inner rod and a new outer casing can be added to the rear end connecting portion of the inner rod and the rear end connecting portion of the outer casing. A double-tube hole drilling device, The downhole hammer has a hammer main body portion located inside the outer casing in the radial direction, and a diameter-expanding portion that protrudes radially outward from the hammer main body portion in front of the outer casing. In a state of being connected to the drive mechanism, the rear end connecting portion of the inner rod is located in front of the rear end connecting portion of the outer casing, and the axial distance from the outer casing to the diameter-expanding portion is set longer than the axial distance from the rear end connecting portion of the outer casing to the rear end connecting portion of the inner rod in a state of being connected to the drive mechanism. A double-tube hole drilling device.

2. The double-tube hole drilling device according to claim 1, wherein the outer casing has a ring bit that protrudes radially inward from the inner peripheral surface of the outer casing and is close to the outer peripheral surface of the hammer main body portion.

3. The double-tube hole drilling device according to claim 1 or 2, wherein the inner rod has a protrusion that protrudes radially outward and is close to the inner peripheral surface of the outer casing.

4. The double-tube hole drilling device according to any one of claims 1 to 3, wherein the hammer main body portion has a mud discharge passage that communicates with the gap between the inner rod and the outer casing and opens in front of the outer casing.

5. A hole drilling method using a double-tube hole drilling device, The double-tube hole drilling device is, An inner rod having a downhole hammer at its front end, and an outer casing into which the inner rod is inserted. The rear end connecting portion of the inner rod and the rear end connecting portion of the outer casing are connected to a drive mechanism to perform hole drilling. In a state separated from the drive mechanism, a new inner rod and a new outer casing can be added to the rear end connecting portion of the inner rod and the rear end connecting portion of the outer casing. The down-the-hole hammer has a hammer main body portion located radially inside the outer casing, and a diameter-expanded portion that protrudes radially outward from the hammer main body portion in front of the outer casing. In a state where it is connected to the drive mechanism, the rear-end connecting portion of the inner rod is located in front of the rear-end connecting portion of the outer casing, and the axial distance from the outer casing to the diameter-expanded portion is set to be longer than the axial distance from the rear-end connecting portion of the outer casing to the rear-end connecting portion of the inner rod in a state where it is connected to the drive mechanism. After operating the drive mechanism to excavate the ground with the down-the-hole hammer and advancing the inner rod and the outer casing in an oblique direction or a horizontal direction to perform hole drilling, when adding a new inner rod and a new outer casing, a step of separating the drive mechanism from the rear-end connecting portion of the outer casing; a step of retracting the inner rod while the diameter-expanded portion remains in a diameter-expanded state to expose the rear-end connecting portion of the inner rod from the rear-end connecting portion of the outer casing; a step of adding a new inner rod to the rear-end connecting portion of the inner rod and adding a new outer casing to the rear-end connecting portion of the outer casing; a hole-drilling method including a step of connecting the new inner rod to the drive mechanism, advancing the new inner rod, and then connecting the new outer casing to the drive mechanism.

Images