JPH09144475A - Excavator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve safety by installing a cover member freely moved towards the front of a cutter along the top plate of an adit to an excavator with the cutter. SOLUTION: The upper plate of the upper frame 26 of a front-section frame 23 is formed in a two-ply shape while an external plate in the upper plate is brought to a slidable state to an internal plate and a cover member 95 is prepared. The front end of the piston rod 97a of a cylinder 97 mounted on the frame 26 is connected to a cover 95, and the cover 95 is freely projected or retreated to or from the front of a cutter 21. A machine body is retreated slightly and an operator M enters into a space between a facing 16 and the cutter 21 at the time of bit exchange during excavation and maintenance and inspection. Since a top plate 13 on the facing 16 side is not timbered at that time, the cover 95 is projected to the front of the upper section of the cutter 21, and the fall of rocks, etc., from the top plate 13 are prevented. Accordingly, since safety can be ensured while the machine body need not be retreated largely from the facing, excavation can be conducted efficiently.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an excavator for excavating underground to form a side gallery in a coal mine.

[0002]

2. Description of the Related Art Generally, as a method for mining underground coal, a long wall type mining method as shown in FIG. 8 is known. This long-wall type mining method excavates parallel roadway tunnels 2 and 3 on both sides of a coal seam 1 to be mined, and also connects the tips thereof to excavate a tip tunnel 4 and a cutter loader (drum) to the tip tunnel 4. An excavating machine such as a cutter is installed, the long wall of the tip gallery 4 is cut toward the front side (direction of arrow a in the figure), and the mine is scraped out to the gallery 2 or 3 and carried out by a belt conveyor or the like.

As a machine for excavating the roadside tunnels 2, 3, a tunnel excavator (continuous minor) 5 as shown in FIG. 9 is known. In this tunnel excavator 5, a truncated cone-shaped excavating head 8 is provided at the tip of a boom 7 extending in front of the machine body 6, and the boom 7 is swung up and down or left and right to have a predetermined cross-sectional shape. It is supposed to be drilled in. The excavated coal and debris are scraped by the loading device 9 provided at the front of the machine body, transferred by the conveyor 10 extending rearward in the center of the machine body, and loaded on the transport vehicle 11 that follows and travels backward. Has become. This tunnel excavator 5 is normally operated by an operator and runs on a crawler 12.

[0004]

By the way, the excavated tunnels 2, 3 and 4 are designed to be supported and maintained by sequentially inserting lock bolts into the roof and side walls thereof. At the time of inspection or replacement, the tunnel excavator 5 must be retracted from the position of the face to the position where the lock bolt is already inserted in order to ensure the safety of the operator. For this reason, there is a problem in that the digging efficiency is deteriorated because the procedure of moving forward again after finishing the inspection work and the like has to be performed.

[0005]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides an excavator having a cutter for excavating a natural ground, which is movable forward along the roof of a tunnel formed by the cutter. It is provided with a cover member. With this configuration, the roof in the vicinity of the face can be substantially supported, and the bit replacement work of the cutter can be performed without retreating the machine body significantly.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 and FIG. 4 show a case where the present invention is applied as a machine for excavating and forming the roadside tunnels 2 and 3 in a coal mine. This excavator includes a cutter 21 for excavating a natural ground (coal bed or bedrock) 14 in an oval cross-sectional shape that is long in the left-right direction when viewed from the front, and a roadside tunnel 2 formed by excavation that is connected to the rear of the cutter 21. , 3 and a frame 22 that supports the peripheral walls. A cover member 95 is provided on the front end side of the frame 22 so as to be movable forward of the cutter along the roof 13 of the tunnels 2, 3.

First, the structure of the frame 22 will be described. The frame 22 is appropriately divided into front and rear in the direction of excavation, and the front frame 23 and the rear frame 24 thereof are substantially the same.
A main body frame 25 that is in contact with the floors of the roadside tunnels 2 and 3 and that constitutes the main body of the machine, and an upper frame 2 that supports the roof 13
6 and left and right side frames 27, 28 that support the side walls. And these frames 25 ... 28 are
It is arranged at a predetermined interval in the circumferential direction and has an outer shape (oval shape) substantially corresponding to the excavated cross section by the cutter 21. That is, the upper frame 26 has an upper plate 29 having a linear cross section, and is assembled flat as a whole. The side frames 27 and 28 have outer plates 30 having an arc cross section.
It is assembled with 31. Body frame 25
Is a rectangular lower part 33 having a straight cross-section bottom plate 32, vertical parts 34 standing on both sides of the lower part 33 in the longitudinal direction, and an upper end of the vertical part 34. The upper horizontal portion 35 and the upper vertical portion 36 are connected to each other, and the whole is assembled into a substantially rectangular parallelepiped shape. A partition wall 37 is attached to the front end of the main body frame 25 to separate it from the cutter 21 side.

The body frame 25 and the upper frame 2
6 and the side frames 27, 28 are provided with expansion / contraction jacks 38, 39, respectively, so that the diameter can be reduced toward the inside of the body, and guides 40, 41 for guiding the expansion / contraction are provided. Has been. In the expansion / contraction jack 38 for the upper frame 26, the cylinders 42 are vertically attached to the front and rear of the respective upper and lower vertical portions 36 of the main body frame 25, and the tip of the piston rod 43 protruding and retracted from the cylinder 42 is the upper frame. It is connected to the lower surface of 26. That is, the upper frame 26 is the upper frame 2
It is movable within a predetermined lifting range within the distance between the lower surface of 6 and the upper surface of the upper vertical portion 36 of the main body frame 25. As shown in FIG. 6, the guide 40 is composed of a cylindrical body 44 erected on the upper end of each vertical portion 34, and a columnar body 45 hung coaxially with the cylindrical body 44 from the upper frame 26.
The pillar 45 slides in the cylinder 44 to guide the up and down movement of the upper frame 26. Further, the expansion / contraction jacks 39 for the left and right side frames 27, 28 are
The jack main bodies 46 are provided above and below and on the both sides of the main body frame 25, respectively, and the tip ends of the piston rods 47 are attached to the inner surfaces of the side frames 27 and 28, respectively. And guide 41
Is a column portion 48 which is provided in parallel in the vicinity of the expansion / contraction jack 39 and horizontally protrudes from the inner surfaces of the side frames 27 and 28;
Cylindrical part 4 which is partitioned in the vertical part 34 and slides the column part 48
9 and 9 (see FIG. 1).

Between the front frame 23 and the rear frame 24, a propulsion jack 50, which is an expansion / contraction means for applying a predetermined propulsive force required for excavation, is provided. The propulsion jacks 50 are arranged at the four upper, lower, left and right corners of the main body frame 25, and the jack main body 51 is provided on the lower portion 33 and the upper vertical portion 52 of the rear frame 24 along the longitudinal direction thereof. Therefore, especially the upper vertical portion 52
Is slightly stronger than the upper vertical portion 36 of the front frame 23 so that the propulsion jack 50 can be sufficiently supported. The left and right expansion / contraction jacks 39 and guides 41 of the rear frame 24 are provided at positions where they do not interfere with the propulsion jack 50. The tip of the piston rod 53 of the propulsion jack 50 is detachably connected to the rear end of the body frame 25 of the front frame 23. That is, the propulsion jack 50 is the expansion / contraction jacks 38, 39.
The expansion and contraction drive is performed in conjunction with the driving of the rear part frame 24 to move the front part frame 23 and the cutter 21 forward with a reaction force to the rear part frame 24, and to move the rear part frame 24 with respect to the advanced front part frame 23. It is designed to attract.

The cover member 95 is formed by the front frame 23.
An upper plate 29 is formed on the upper frame 26 as an outer plate of the two stacked plates and is slidable with respect to an inner plate 96. The upper frame 26 is provided with a cylinder 97, and the tip of the piston rod 97a is connected to the cover member 95, and by extension thereof, projects toward the front of the cutter 21. That is, when exchanging bits during excavation or during maintenance and inspection, as shown in FIG. 1, the aircraft is slightly retracted, and its face 16 and the cutter 2 are moved.
Although the worker M will enter the space between 1 and 1, the roof 13 on the face 16 side is not supported, so the cover member 95 prevents falling stones from the roof 13 and the worker This is to secure the safety of M.

Next, the cutter 21, as shown in FIG.
A pair of left and right main cutters 61 and 62 that rotate around the axis of the excavation direction, and a pair of upper and lower trimming cutters 63 for excavating the portion left uncut by the main cutters 61 and 62 (indicated by the two-dot chain line in the figure). , 64. The main cutters 61 and 62 include a shaft 65 serving as a rotating shaft, three spokes 66 radially extending from the shaft 65, and bits (cutter picks) 67 protruding forward at a predetermined interval in the longitudinal direction of the spokes 66. It consists of and. A bit 68 is also planted in an arc shape at the front end of the shaft 65. Further, a water injection nozzle may be provided on the shaft 65 to inject a spray for dust suppression and cutting spark prevention on the face. The left and right main cutters 61 and 62 are the spokes 6
6 are arranged on the same plane and in a phase relationship such that one spoke 66 enters the middle of the other spoke 66.

As shown in FIG. 1, the shaft 65 extends rearward and is axially supported by the vertical portion 34 of the body frame 26, and a gear 69 is provided at the extending end thereof. The gear 69 is meshed with a gear 71 of an electric motor 70 mounted on the lower portion 33 of the main body frame 26. A speed reducer 72 is provided between the gear 71 and the electric motor 70. That is, the rotational force of the electric motor 70 is appropriately transmitted to the pair of main cutters 61 and 62, and these are rotationally driven in the opposite directions to excavate the front face. Then, as shown in FIG. 3, the outer peripheral end side 66 a of the spoke 66 is detachably divided and is formed so as to become shorter in accordance with the diameter reduction of the frame 22. As for this division structure, for example, the division surfaces 73 of the spokes 66 may be formed in a concavo-convex shape so as to be fitted together, and then fastened with bolts and nuts (not shown). In FIG. 3, only the spokes 66 protruding upward or left and right when the diameter is reduced are shown as a structure that can be shortened, but all the spokes 66 may be formed so as to be shortened.

Further, a bucket 74 is provided on the back side of the spokes 66 so that the excavated coal or rock is picked up and thrown into a conveyor 76 for carrying out via a chute 75. Two chutes 75 are provided corresponding to the left and right main cutters 61, 62, and are inclined downward toward the center of the machine body. As shown in FIG. 1, the conveyor 76 is formed by an endless belt 78 wound around a roller 77 located below and in front of the chute 75. Then, as shown in FIG. 6, the endless belt 78
The conveyance surface side is supported by a guide roller 79 appropriately arranged in the main body frame 25, and after slightly rising, it extends horizontally rearward and is excavated to another conveyor or a transportation vehicle (not shown) located at the rear of the machine body. It is designed to transport coal or rocks.

The trimming cutters 63 and 64 are formed in a sawtooth shape by a cutter body 80 having a predetermined length and bits 81 planted at predetermined intervals along the longitudinal direction thereof, and the main cutters 61 and 62. It is provided at the front end of the front frame 23 near the rear of the bucket 74. That is, the upper trimming cutter 63 is located on the upper frame 26.
Further, the lower trimming cutters 64 are arranged on the lower portion 33 of the main body frame 25, respectively. As shown in FIG. 4, the cutter body 80 is housed in a box-shaped bracket member 82 with the bit 81 exposed, and is supported by a guide rod 83 extending in the left-right direction via a moving block 84. There is. The guide rod 83 is a bracket member 8.
Both ends are supported by two left and right side plates 82a. The moving block 84 is fitted to the guide rod 83 and is slidable in the longitudinal direction thereof. A return cylinder 85 is connected to the moving block 84. The return cylinder 85 is
The cylinder body 85a is provided in parallel with the guide rod 83, and the base end of the cylinder body 85a is a base plate 82b at the rear of the bracket member 82.
Is supported by a bracket 86 on the piston rod 8
The tip of 5b moves through the bracket 87 to the moving block 84.
It is connected to. That is, the trimming cutters 63 and 64 reciprocate in the left-right direction by expanding and contracting the return cylinder 85. The returning range is restricted by a stopper 83a provided on the guide rod 83.

As shown in FIG. 5, the bracket member 82 is provided with an actuator 88 for appropriately moving the trimming cutters 63 and 64 in and out of the machine body. The actuator 88 has a cylinder portion 88.
The base end of a is pivotally supported inside the lower frame 33 or the upper frame 26 via a bracket 89, and the tip of the piston rod 88b is pivotally supported on the back side of the base plate 82b via a bracket 90. And in the vicinity of the fulcrum,
The board 82b is attached to the frames 33, 2 via the bracket 91.
A support shaft 92 for supporting 6 is provided in the left-right direction. In other words, by extending and retracting the actuator 88 to raise and lower the bracket member 82 about the support shaft 92,
The trimming cutters 63 and 64 are movable in and out of the machine body. Therefore, as shown in FIG. 6A, in the normal excavation, the bit directions of the trimming cutters 63 and 64 are tangentially connected to the upper ends and the lower ends of the pair of main cutters 61 and 62. Is held at a predetermined angle θ with respect to the vertical direction, for example, 45 degrees. If necessary, the actuator 88 is retracted, and the actuator 88 shown in FIG.
As shown in the middle part (b), the bracket member 82 is rotated clockwise by an appropriate angle (α) in the drawing, so that the bit 81 is directed toward the inside of the machine body and the bracket member 82.
The whole body is located inside the body. That is, when inspecting or exchanging the bit 81, adjusting the amount of excess digging, or performing bending excavation, the actuator 88 is extended upward and downward or both of them one more than usual, so that the bit 81 projects outside the fuselage. Thus, it can be rotated and held at any position up to the maximum position (P). When the trimming cutters 63 and 64 are directed toward the inside of the body, the bracket member 82 may interfere with the partition wall 37. Therefore, in order to avoid this, FIG.
As shown in (b), the portions of the frames 33 and 26 supporting the actuator 88 are formed to be slidable in the front-rear direction, and the other actuator 93 is extended so that this portion can be advanced by an appropriate distance L. You may
In addition, an inclined guide plate 82c for appropriately guiding the coal excavated by the trimming cutters 63 and 64 is formed on the inner side of the bracket member 82 in the body. That is, on the upper side, coal or the like is guided to the chute 75, and on the lower side, it is pushed forward by excavation and scooped by the buckets 74 of the main cutters 61 and 62. Further, the bracket member 82 is provided with an auxiliary guide 94 in parallel behind the guide rod 83 in order to sufficiently receive the excavation reaction force of the trimming cutters 63 and 64.

In addition, as shown in FIG. 6, the main body frame 25 is provided with a vent pipe 98 for ventilation. Then, each jack (3
8, 39, 50 ...), a cab (not shown) for controlling excavation, and the like are provided. This operator's cab may be provided on the side of the wellhead separated from the frame 22 so that the excavation operation can be performed by remote control. Further, on the rear deck (not shown) of the rear half frame 24, a rock bolt 99 is attached to the roof 13 of the roadways 2 and 3.
And a bolt insertion device 100 for insertion into the side wall. The bolt inserting device 100 is not necessarily provided in the rear deck, but may be separately mounted in a traveling vehicle that follows the excavation.

Next, by using the excavator having the above structure,
The process of excavating 3 will be described (see FIG. 7). First, while keeping the propelling jack 50 in a contracted state, the front frame 23 has an outer diameter slightly smaller than the cross section excavated by the cutter 21, so that the jacks 38, 3 for reducing the diameter are provided.
9 is degenerated to a reduced diameter state. That is, an appropriate gap S ₁ is formed between the roof 13 and the upper surface of the upper frame 26, and the side wall and the side frames 27, 28 are formed.
A similar gap (not shown) is also formed between and.
The rear half frame 24 includes the diameter reducing jacks 38, 3
By the extension of 9, the main frame 25, each frame 2
6 ... 28 are pressed against the peripheral wall over the entire circumference as appropriate (a in FIG. 7). In this state, the main cutters 61 and 6
2 and the trimming cutters 63 and 64 are driven, and the conveyor 76 is also driven. And propulsion jack 5
When 0 is extended, the main cutters 61 and 62 excavate substantially the entire face of the cutting face 16 due to the rotation and pressing force thereof, and the trimming cutters 63 and 64 cause the main cutters 61 and 6 to excavate.
The portion left uncut by 2 is excavated (b in FIG. 7).
At this time, the trimming cutters 63 and 64 only cut at the positions where the upper ends and the lower ends of the pair of main cutters 61 and 62 are tangentially connected to each other. ), Due to the nature of the coal seam, if cracks occur, it is easy for the rocks to become damaged due to its own weight or vibration.
Peeled off from The coal or rock excavated by the cutter 21 is scooped by the bucket 74, and the chute 7
5 and the conveyor 76 carry out to the rear.

When the propelling jack 50 has been dug to the maximum extent, the expansion / contraction jacks 38, 39 of the front frame 23 are extended to bring the upper frame 26 and the side frame 27 into pressure contact with the peripheral wall. With
The expansion / contraction jacks 38, 39 of the rear frame 24 are reduced to separate the frames 26, 27 from the roof 13 and the side walls. That is, an appropriate gap S ₂ is formed between the upper surface of the upper frame 26 of the latter half frame 24 and the roof 13 (c in FIG. 7). In this state, the propulsion jack 50 is retracted, and the rear frame 24 is pulled forward (d in FIG. 7). In parallel with this pulling, or after pulling is completed, a hole for inserting a lock bolt is made in the roof 13 and the side wall of the dug section with a drill provided in the bolt inserting device 100, and the hole is used to stabilize. The chemical liquid for the purpose of injection is injected, and the lock bolt 99 is inserted and fixed with the nut. In this support, a net or the like may be used together to fix the lock bolt 99. If the propulsion jack 50 is degenerated to the minimum (e in FIG. 7),
The diameter of the front frame 23 is reduced again, and the rear frame 2
4 is expanded and returned to the initial state (a in FIG. 7), and the excavation is continued.

When the digging time or digging length is reached, the bits 67 and 68 of the main cutters 61 and 62 are inspected and partially replaced. In this case, in a state where the propulsion jack 50 is extended and the front portion frame 23 is reduced in diameter (c in FIG. 7), the propulsion jack 50 is contracted again, the front portion frame 23 is slightly retracted, and the face 16 and the main face 16 are removed. Cutter 6
A space is provided between 1 and 62 for the worker M to enter (see FIG. 1). Next, the actuator 88 of the upper trimming cutter 63 is contracted, and the bracket member 82 is rotationally moved toward the inside of the machine body so as to be separated below the level of the upper plate 29. And the cylinder 97 of the upper frame 26
Is extended to advance the covering member 95 forward. As a result, the front roof 13 is covered by the cover member 95, and the safety in the space below it is ensured. Further, the trimming cutters 63 and 64 may be inspected and replaced at the same time as the maintenance of the main cutters 61 and 62. In this case, the lower trimming cutter 64 is also retracted inside the body by reducing the actuator 88. It should be noted that the retracting distance of the front frame 23 is preferably such that the main cutters 61, 62 return to the position where the trimming cutter 63 cuts the roof 13 horizontally. It is also conceivable that the board 13 is provided with elasticity so as to get over even if some protruding portions remain, or that the protruding portions can be cut by the cylinder pressing force. In this case, the retreat distance may be the minimum necessary distance corresponding to the working space.

When the excavation reaches the planned length, the expansion / contraction jacks 38, 39 are retracted to the maximum extent, and the outer diameter of the frame is reduced so as to be significantly smaller than the cross section of the roadways 2, 3 (Fig. (Solid line 3). That is, the frames 26 ... 2
A large gap is formed between 8 and the roof 13 and the side wall. Then, the connection between the piston rod 53 of the propulsion jack 50 and the front part frame 23 is released, and the rear half part frame 24 is connected to the towing vehicle traveling in the roadside tunnels 2, 3. Then, the rear half frame is carried out by running the towing vehicle to the pit side. At this time, the second half frame 2
By slightly lifting the rear end of No. 4, only the front end is in contact with the ground, and the frictional resistance is small. For this pulling, a roller or the like may be provided below the front end of the rear half frame 24. If the natural ground 14 is a coal seam, the excavation surface (bottom surface 15) is smooth and the friction coefficient μ is 0.
Since it is about 4, it does not cause a big obstacle in towing, and it can be quickly carried out by a relatively small towing vehicle. When this unloading is completed, the towing vehicle is subsequently connected to the front half frame 23. At this time, if the lower trimming cutter 64 is in the same position as the outer surface of the frame or is left in a protruding state, the frictional resistance due to grounding increases,
Further, since there is a possibility of damage to the cutter, the actuator 88 is reduced in size so that it is accommodated inside the body. Then, as the tow vehicle travels, it is carried out in the same manner as the latter half frame 24. In some cases, the front half frame 23
Alternatively, the rear half frame 24 may be carried out by a towing vehicle while being connected to the latter half frame 24.

When the excavation of the roadside tunnels 2 and 3 is completed, the tip tunnel 4 connecting the tips thereof is excavated (see FIG. 8 above). At the time of this excavation, the direction may be changed to a right angle so that the same excavator can be used to continue excavation in the roadside roads 2 and 3, but it is difficult to change the direction in a narrow space, and the tip roadway 4 is Since it is extremely short as compared with the layer tunnels 2, 3, the conventional tunnel excavator (see FIG. 9) is carried in and excavated after the excavator of the present invention is carried out.
When this excavation is completed, the drum cutter is carried in and installed in the tip tunnel 4 to excavate the coal seam between the two roadside tunnels 2 and 3, and full-scale coal mining is performed.

In this way, the upper frame 26 is provided with the cover member 95 which is movable in the excavation direction, and the main cutter 61,
During the inspection / replacement work of 62, since the cylinder 97 is driven to project toward the front of the cutter along the roof 13, the roof 13 between the face 16 and the main cutters 61, 62 is substantially removed. It can be supported, and the safety of the worker M is secured. Therefore, it is not necessary to retreat the airframe significantly to the section where the insertion of the lock bolt 99 is completed, the maintenance work can be performed quickly, and the excavation of the roadside tunnels 2 and 3 can be performed efficiently.

Further, in this embodiment, a cutter 21 for excavating with an oval cross section and a frame 22 for supporting the peripheral walls of the roadside tunnels 2 and 3 formed by the cutter 21 are provided.
Moreover, since the frame 22 is formed so that its diameter can be freely reduced, excavation of the entire cross section of the tunnel can be performed efficiently at once, and the lock bolt 9
By carrying out the construction of 9 in parallel, the excavation efficiency can be greatly improved, and the post-excavation can be carried out very easily and quickly, and the construction period of the excavation and coal mining of the roadside tunnels 2 and 3 can be greatly improved. It can contribute to shortening. Since the frame 22 is divided into front and rear and the propulsion jack 50 is provided between them,
In combination with the structure in which the frame can be freely expanded and contracted, the propulsion reaction force can be reliably obtained without depending on the frictional force with the tunnel floor surface due to the weight of the machine body, and the excavation speed can be further improved. It should be noted that the circumferential division interval and expansion / contraction range of the frame 22 may be selected so long as they do not hinder the excavation and retreat, and should be appropriately selected according to the size of the excavation cross section, the protruding length of the head of the lock bolt 99, and the like. Kimono.

The present invention is not limited to the excavator for the roadside gallery 22 illustrated, but can be widely applied to tunnel excavation under similar construction conditions. Further, the configurations of the cutter, the frame and the like are not limited to the illustrated examples, and can be applied to an excavator or the like in which the cutter is supported by a beam.

[0026]

In summary, according to the present invention, it is possible to secure the safety of the operator when exchanging the bits of the cutter, etc., and it is not necessary to retreat the machine body from the face, so that the tunnel excavation can be performed efficiently. It can be carried out.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing an embodiment of the present invention.

FIG. 2 is a view taken along the line AA of FIG. 1;

FIG. 3 is a front view for explaining the operation of FIG.

FIG. 4 is a plan view of a main part of FIG. 1;

FIG. 5 is a side view of FIG. 4;

FIG. 6 is a sectional view taken along line EE of FIG. 1;

FIG. 7 is a side sectional view showing an excavation process by the excavator of FIG. 1.

FIG. 8 is a perspective view for explaining the long-wall mining method in a coal mine.

FIG. 9 is a perspective view showing a conventional machine.

[Explanation of symbols]

 2,3 Coastal mine (road) 13 Roof 14 Ground 16 Cutting face 21 Cutter 22 Frame 95 Covering member

Claims (1)

[Claims] 1. An excavator having a cutter for excavating the natural ground, characterized by comprising a cover member movable forward of the cutter along a roof of a gallery formed by the cutter.