US3655001A

US3655001A - Large diameter earth drill

Info

Publication number: US3655001A
Application number: US8664A
Authority: US
Inventors: Bernard A Hoffman
Original assignee: Schramm Inc
Current assignee: Schramm Inc
Priority date: 1970-02-04
Filing date: 1970-02-04
Publication date: 1972-04-11
Anticipated expiration: 1989-04-11

Abstract

A system for producing large-diameter, air-drilled holes through rock comprises a hollow, rotatable drill stem having a large bit at its lower end, and surrounded by a pipe which is relatively narrow compared to the hole diameter, which forms between itself and the drill stem, an annular passage. Air is blown downwardly through the drill stem, emerges at an opening at the location of the bit, and carries cuttings through the annular passage to the surface. A vacuum is drawn in a dust diverter immediately above the bit to insure that the cuttings enter the annular passage. Air descending through the drill stem under pressure operates a piston which imparts a hammering action to the bit. Drill stem sections and outer pipe sections may be added as required.

Description

United'States Patent a 11 1 3,655,001 1451 Apr. 11,1972

3,297,100 l/l967 Crews ..17s/21s x Prime/y Eraminer bavid H. Brown- Attorney-Bauer, Smith Harding [57] ABSTRACT A system for producing large-diameter, air-drilled holes through rock comprises a hollow, rotatable drill stem having a large bit at its lower end, and surrounded by a pipe which is relatively narrow compared to the hole diameter, which forms between itself and the drill stern, an annular passage. Air is blown downwardly through the drill stem, emerges at an opening at the location of the bit, and carries cuttings through the annular passage to the surface. A vacuum is drawn in a dust diverter immediately above the bit to insure that thecuttings enter the annular passage. Air descending through the drill stern under pressure operates a piston which imparts a hammering action to the'bit. Drill stem sections and outer pipe sections may beadded as required.

16 Clalrns,5 Drawlng Figures BACKGROUND OF THE INVENTION This invention relates to apparatus for producing large diameter holes in earth and rock for the purpose ofsetting poles, piling and the like. Typical diameters are in the range of 16 to 24 inches, although still larger diameters are sometimes required in certain applications. I In the past, these holes have been produced by blasting and also by producing lead holes of small diameter, for example 6 inches, and subsequently reaming to the required dimensions. Attempts to produce large holes have also been made involving the use of large diameter drills. The equipment required was bulky, and in many instances several passes had to be made with the drill because of difficulties in removing cuttings.

Air drilling has simplified the removing of cuttings in small diameter drills. Typically, a rotating drill stem is provided with a central passage and a surrounding annular passage. Ordinarily, air is introduced under pressure through the central drill stem passage, and cuttings are removed along with air through the annular passage. In reverse circulation" air drilling, air is introducedunder pressure through the annular passage, and cuttings are removed along with the air through the central passage.

Heretofore, neither of these methods has been successfully employed in the drilling of large diameter holes.

Numerous difficulties have been encountered in air drilling. The production of 'dust clouds by the air stream at the bit has resulted in unpleasant, and possibly hazardous conditions for drill operators and other persons in the vicinity of a drilling operation.

SUMMARY OF THE INVENTION In accordance with this invention, a rotating drill stem having a central passage is located within a stationary pipe forming an annular passage surrounding the drill stem. Air is introduced under pressure through the central passage. It exits from the central passage at the location of a bit mounted at the lower end of the drill stern, and carries cuttings and dust upwardly through the annular passage. A dust diverter is mounted on the stationary pipe just above the bit. The diameter of the lower end of the dust diverter is nearly as great as that of the bit. The dust diverter, however, narrows toward the location at which it is connected to the pipe. The internal diameter of the pipe and the external diameter of the drill stern are chosen so that the annular passage between them has a cross-section which produces a high rising velocity of the air passing through the annular space. Cuttings can thus be carried out efficiently without employing large volumes of flushing air. The annular space, however, is adequately large to prevent any accumulation of cuttings within it.

The pressure within the annular passage and within the dust diverter is at a lower pressure than the space outside the dust diverter. Therefore, air carrying dust tends to enter the dust diverter, and does not enter the atmosphere through the space between the pipe and the wall of the hole being drilled.

Since the air entering the hole passes through the central passage of the rotating drill stern, it can be conveniently used to power a vertically reciprocating piston arranged to impart a hammering action to the bit in order to aid cutting.

The apparatus is relatively simple and light in weight. The outer pipe is preferably non-rotating, allowing simple collection of cuttings and conserving rotational power. The most 'important advantage of the apparatus, however, is its ability to produce large diameter holes in a single pass.

The principle object of the invention, therefore, is to drill large diameter holes in earth and rock quickly and reliably.

Another object is to provide an air drilling system which is not liable to break down as a result of blocking of an air passage.

Still another object is to provide an air drilling system in which air under pressure serves not only the purpose of removing cuttings, but also operates a hammering device.

A still further object is to eliminate substantially the escape of dust into the atrnospherefrom a hole being produced by air drilling.

Still another object of the invention is to provide an air drilling system in which drill stem sections can be readily attached to each other in order to increase the depth of the hole beingdrilled. v

Other objects will become apparent from the following description read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENTS Various mechanisms may be used to effect rotation of the drill bit. Preferably, however, the entire length of the drill stem is rotated, rotational power being applied at or near the upper end of the drill stem.

FIG. 1 shows a drill stem section 10 having a bore 12 with a substantially constant diameter. A bull gear 14 is keyed to section 10, and meshes with a drive gear 16 rotated by a motor 18 (FIG. 5) through a shaft 20.

An air connector assembly 22, having an internal passage 24 bent at right angles, is connected to the upper end of drill stem section 10 so that passage 24 communicates with passage 12 for the introduction of a stream of air downwardly into the drill stem. Packing is provided at 26 to prevent leakage at the connection.

The connections between the drill stem sections of the assembly may take various forms. Conveniently, tapered threads may be used. At the lower end of drill stem section 10, tapered threads 28 are provided which connect to threads at the upper end 30 of a drill stem section 3 2.

A hollow member 34 has a shoulder 36 at its lower end carrying packing 37 which prevents the passage of air upwardly between shoulder 36 and drill stem section 32 into the interior 38 of member 34. A ring-shaped cap 39 is bolted to the top of member 34 to close interior 38. It allows stem section 32 to extend through its central opening 40 and downwardly through the interior 38 .of member 34.

The outer race 41 of a spherical roller bearing rests on a shoulder 42 of member 34. It is clamped in position by cap 39. Stem section 32 is provided with a shoulder 50 which rests on the inner race 52 of the bearing. A nut 54 is threaded onto stem section 32 and clamps race 52 against shoulder 50.

A cylindrical pipe section 56-is welded at 58 to member 34.

A transversely extending tubular member 60 is welded into an opening, the edge of which is indicated at 62. Its internal passage 63 is in communication with the internal passage 64 of pipe section 56.

Within internal passage 64, stern section 32 is provided with a pair of

shoulders

65 and 66, by which its diameter is increased. lts bore 68, however, remains constant in diameter.

As shown in FIGS. 1 and 3, a ring 70 is welded to the exterior of pipe section 56 at its lower end to provide a flange to which there is bolted a spider 72 having a circular central opening 73 through which stem section 32 extends. The clearance between opening 73 and the stem section permits the stern section to rotate freely but supports the stem section .against substantial radial movement. The spider provides openings at 74, 76 and 78.

A second and longer pipe section 80 is welded to the underside of spider 72.

Tapered threads 84 are provided atthe lower end of stem section 32. These threads couple with threads in member 86. (It should be noted that threads 84 and member 86 are duplicated in FIG. 2).

At the lower end of pipe section 80, there is welded a ring 88 fonning a flange to which there is bolted a spider 90. Ring 88 and spider 90 are similar to ring 70 and spider 72 respectively.

Pipe section 92 is welded to the underside of ring 90 at 94. Section 92 surrounds a drill stem section 96, which comprises an upper section 98 in which there is mounted a cylindrical valve member 100 held rigidly in place within section 98 by a spider 102. Spider 102 is integral with the valve member. Section 98 has an internal cylindrical wall 104 in which the upper end 106 of a piston 108 is arranged to reciprocate vertically.

Lower section 110 of drill stem section 96 is threaded to the upper section 98. Section 110 is the outer casing of the reciprocating piston device. The inner wall 112 of section 110 forms a cylinder in which the lower end 114 of the piston can reciprocate. The diameter of the cylinder formed by wall 112 os larger than the diameter of the cylinder formed by wall 104, and the respective ends 106 and 114 of piston 108 differ in diameter accordingly. An internal passage 116 within the piston leads from an opening 118 in the upper end 106 to a transverse opening 120 in a part 121 of the piston having a reduced diameter below part 114. A passage 122 leads from space 124 between wall 112 and the piston to an opening 126 in projection 128 at the bottom of the piston. A retaining ring 130 is provided in the wall 112 in order to prevent the piston from moving below the position at which the ring is engaged by the lowermost shoulder 132 of part 114 when the stem section 134 is removed.

Drill stem section 134, which acts as an anvil, is keyed by the cooperation of

teeth

136 and 138 so that it rotates with drill stem section 110 while it is allowed to reciprocate vertically under the hammering action imparted by piston 108. The lower limit of its reciprocation is established by the engagement of shoulder 140 on section 134 with shoulder 142 at the bottom of stem section 110.

Stem section 134 is rigidly connected to bit 144 through stem section 160.

Reciprocating piston drilling devices of the type just described are well known. Briefly, the operation is as follows: referring particularly to FIG. 2,- air travelling downwardly through passage 68 passes through the central passage 116 in the piston causing-the piston to be lifted since the effective area underneath the piston is greater than that above it. When projection 128 clears the opening in the top of stem section 134 in which it normally fits, air is allowed to pass into central passage 146. The momentum of the piston,however, carries it still further upwardly so that the flow of air into passage 116 is cut oil by valve 100. The piston then descends violently and imparts a blow to the top of stem section'134. So long as air is supplied, the reciprocation of piston 108 will continue automatically.

It has been assumed that the bit has been resting on the bottom of the hole being drilled. It will be apparent that, if the bit is allowed to hang, the upper end of stem section 134 will be sufficiently spaced from the lower end of the pistonthatain will freely flow through the central passage of the piston and downwardlythrough passage 146. Under these conditions, the piston will not reciprocate. 1

A ring 148 is welded at the bottom of pipe section 92, and a spider 150 is bolted to the ring. Ring 148and spider 150 are similar to those previously described. A frusto-conical member 152 is welded at its narrow end to the underside of spider 150. The diameter at the narrow end is approximately that of pipe section 92.

At the wide end of member 152, there is welded a spider 154 (also shown in FIG. 4). Spider 154 is similar to the spiders previously described but larger in size. A ring 156 is bolted to the underside of the spider, and a cylindrical skirt 158 is welded to the ring.

The assembly including member 152, spider 154 and skirt 158 constitutes a dust diverter. The diameter of member 158 should be as large as will be permitted by the hole being drilled. It should be no larger that the bit diameter, however. If the bit is replaced by one having a larger diameter, member 158 may be replaced by a member having a larger diameter. This can be accomplished easily by removing the bolts fastening ring 156 to spider 154 and bolting a substitute skirt and ring assembly in place.

Bit 144 is threaded into an enlarged part 160 of stem section 134. The bit has a central passage 162 which communicates with passage 146, and which has a central opening 164 in a small lead bit 166.

Oblique passages

168 and 170 deliver air from the central passage to

cones

172 and 174 respectively at the ends of

arms

176 and 178. Additional oblique or transverse passages may be provided as desired.

FIG. 5 shows gear box 180 and a bearing box 182 surrounding drill stem section 10.

Arms

184 and 186 connect the bearing box respectively to drive

chains

188 and 190 by which the drilling apparatus may be raised and lowered.

Air connector assembly 22 is connected to a compressor 192 which delivers air to it under a pressure typically 250 lbs. per square inch. Transverse pipe 60 is connected to a chip collection box 194 through a flexible hose 196 which allows for vertical movement of the drilling apparatus. Box 194 has a sloped bottom 196 and a hinged door 198 which opens under the weight of collected cuttings when a sufficient amount has been collected. A blower 200 is connected through a flexible hose 202 and through an opening 204 to the interior of the box. A baffle 206 is positioned within the box so that cuttings entering through opening 208 strike it and fall to the bottom. The opening at 204 is on the opposite side of the bafile.

Blower 200 draws a vacuum in the space between the drill stem ends of the outer pipe sections. The dimensions of the drill stem and the pipe sections are preferably related in such a way that the air velocity in the space between the drill stem and the pipe. is in the vicinity of 3,000 feet per minute. This velocity is sufficient to remove cuttings, but not so great as to produce erosion of mechanical parts. Typically, the outside diameter of drill stem section 32, in the area between

spiders

72 and 90, would be 5 V4 inches while the internal diameter of pipe section 80 would be 7 '76; inches.

Substantially lower air velocities may be used t0 accomplish removal of cuttings if a foam-producing material is introduced into the air stream in accordance with the method described in I US. Pat. No. 3,130,798, issued on Apr. 28, 1964 to Harold J. Schramm and Alfred N. Gustafson.

lnoperation, the air from compressor 192 passes through the drill stem, actuates the'piston which delivers a rapid succession of blows to the bit. The combination of bit rotation and vertical reciprocation produces efi'icient cutting through rock. The air stream not only operates the reciprocating piston, but also emerges through openings at the location of the bit and carries cuttings upwardly through the annular space surrounding the drill stem and to the collection box.

Since blower 200 maintains a negative pressure underneath the dust diverter, dust produced by cutting tends to enter. the

dust diverter, and does not pass .into the space between the wall of the hole and the pipe sections.

The small diameter of the pipe sections compared to thebit diameter permits the reduction of high rising air velocities with a minimum volume of air, and also reduces weight of the drilling equipment. Additional drill stern sections and pipe sections may be added as drilling progresses. The use of ring and spider assemblies is a convenient method for attaching pipe sections, and the spiders provide lateral support for the rotating drill stem.

In summary, the drilling system in accordance with this in vention makes possible the production of large diameter holes with' minimum air volume and minimum equipment weight, and provides a relatively dust free condition for the operator.

1. Apparatus for air drilling large diameter holes comprising a rotatable drill stern having a large diameter bit attached to its lower end,

means for imparting rotational movement to said drill stem, a bore entending through said drill stem and having at least one opening at the location of said bit, means for introducing air under pressure into said bore, a non-rotating pipe surrounding said drill stem, means providing a seal between said pipe and said stem at the upper end of said pipe, an outlet opening near the upper end of said pipe, means for drawing a vacuum at said outlet opening, and means providing an enlarged opening at the lower end of said pipe, said opening having a larger diameter than said pipe, but no greater than the diameter of said bit. 2. Apparatus for air drilling large diameter holes comprising a drill stem having a large diameter bit attached to its lower end,

means for imparting a cutting action to said bit, a bore extending through said drill stem and having at least one opening at the location of said bit, means for introducing air under pressure into said bore, a pipe surrounding said drill stem, means providing an outlet opening near the upper end of said pipe, means for drawing a vacuum at said outlet opening, and means providing an enlarged opening at the lower end of said pipe, said opening having a larger diameter than said pipe, but no greater than the diameter of said bit. 3. Apparatus for air drilling large diameter holes comprising a drill stem having a large diameter bit attached to its lower end,

means for imparting vertical reciprocatory movement to said bit, a bore extending through said drill stem and having at least one opening at the location of said bit, means for introducing air under pressure into said bore, a non-rotating pipe surrounding said drill stem, means providing an outlet opening near the upper end of said pipe, means for drawing a vacuum at said outlet opening, and means providing an enlarged opening at the lower end of said pipe, said opening having a larger diameter than said pipe, but no greater than the diameter of said bit. 4. Apparatus for air drilling large diameter holes comprising a drill stern having a large diameter bit attached to its lower end,

means for imparting rotational movement to said bit, a bore extending through said drill stem and having at least one opening at the location of said bit, means for introducing air under pressure into said bore, air-powered reciprocating means receiving air from within said bore for imparting a hammering action to said bit, a non-rotating pipe surrounding said drill stem, an outlet opening near the upper end of said pipe, means for drawing a vacuum at said outlet opening, and means providing an enlarged opening at the lower end of said pipe, said opening having a larger diameter than said pipe, but no greater that the diameter of said bit. 5. Apparatus for air drilling large diameter holes comprising a drill stem having a large diameter bit attached to its lower end, means for imparting rotational movement to said bit, a bore extending through said drill stem, at least one opening at the location of said bit, means for introducing air under pressure into said bore, air-powered reciprocating means receiving air from within said bore for imparting a hammering action to said bit, means for discharging air exhausted from said reciprocating means through said opening, a non-rotating pipe surrounding said drill stern, an outlet opening near the upper end of said pipe, means for drawing a vacuum at said outlet opening, and

means providing an enlarged opening at the lower end of said pipe, said opening having a larger diameter than said pipe, but no greater than the diameter of said bit.

6. Apparatus for air drilling large diameter holes comprising a rotatable drill stem having a large diameter bit attached to its lower end,

means for imparting rotational movement to said bit,

a bore extending through said drill stem and having at least one opening at the location of said bit,

means for introducing air under pressure into said bore,

a non-rotating pipe surrounding said drill stem,

means providing a seal between said pipe and said stem at the upper end of said pipe, an outlet opening near the upper end of said pipe, means for drawing a vacuum at said outlet opening, and

an opening at the lower end of said pipe for collecting air and cuttings from the bottom of a hole being drilled.

7. Apparatus for air drilling large diameter holes comprising a rotatable drill stem having a large diameter bit attached to its lower end,

means for imparting rotational movement to said drill stem, a bore extending through said drill stem and having at least one opening at the location of said bit, means for introducing air under pressure into said bore,

a non-rotating pipe surrounding said drill stem,

means providing an outlet opening near the upper end of said pipe, means for drawing a vacuum at said outlet opening, and

an opening at the lower end of said pipe for collecting air and cuttings from the bottom of a hole being drilled,

said non-rotating pipe comprising a plurality of sections arranged in end-to-end relation, and means for fastening said sections together.

8. Apparatus according to claim 7 in which said drill stem comprises a plurality of drill stem sections arranged in end-toend relationship and means for fastening said drill stem section together.

9. Apparatus for air drilling large diameter holes comprising a rotatable drill stern having a large diameter bit attached to its lower end,

means for imparting rotational movement to said drill stem,

means for introducing air under pressure into said bore,

a non-rotating pipe surrounding said drill stem,

an opening at the lower end of said pipe for collecting air and cuttings from the bottom of a hole being drilled, said non-rotating pipe comprising a plurality of sections connected in end-to-end relation, and means at each connection for fastening said sections together, each said fastening means comprising a flange fastened to the end of one of said sections, a flange fastened to the end of the other section at said connection, and means for fastening said flange in face to face relationship, at least one of said flanges having attached to it spider means having a central opening through which said drill stem extends, said spider means providing at least one opening between said drill stem and said pipe for the passage of air and cuttings upwardly to said outlet opening near the upper end of said pipe.

10. Apparatus according to claim 9 in which said spider means is an integral part of the flange to which it is attached.

11. Apparatus according to claim 9 in which said drill stern comprises a plurality of drill stem sections arranged in end-toend relationship and means for fastening said drill stem section together.

12. Apparatus for air drilling large diameter holes comprising a drill stem having a large diameter bit attached to its lower end,

means for imparting a cutting action to said bit,

means for introducing air under pressure into said bore,

a pipe surrounding said drill stem,

means providing an outlet opening near the upper end of said pipe, means for drawing a vacuum at said outlet opening, 4 means providing an opening at the lower end of said pipe,

and shielding means fastened to the lower end of said pipe for preventing dust produced by the cutting action of said bit from passing upwardly to the surface through the space between the pipe and the wall of the hole being drilled. 13. Apparatus according to claim 12 including a skirt having a maximum diameter not exceeding that of said bit and means detachably fastening said skirt to the shielding means.

14. Apparatus for air drilling large diameter holes comprising a drill stem having a large diameter bit attached to its lower end.

means for imparting a cutting action to said bit, a bore extending through said drill stem and having at least one opening at the location of said bit,

means for introducing air under pressure into said bore,

' a pipe surrounding said drill stem,

a collection box for cuttings, said box having an inlet opening, an outlet opening and at least one baffle obstructing a straight path between said inlet and outlet openings,

means providing an opening near the upper end of said pipe,

means for drawing a vacuum,

a conduit connecting said opening near the upper end of said pipe to the inlet opening of said collection box, and means connecting said means for drawing a vacuum to the outlet opening of said collection box.

15. Apparatus according to claim 14 in which said conduit is a flexible conduit.

16. Apparatus according to claim 14 including shielding

Claims

1. Apparatus for air drilling large diameter holes comprising a rotatable drill stem having a large diameter bit attached to its lower end, means for imparting rotational movement to said drill stem, a bore entending through said drill stem and having at least one opening at the location of said bit, means for introducing air under pressure into said bore, a non-rotating pipe surrounding said drill stem, means providing a seal between said pipe and said stem at the upper end of said pipe, an outlet opening near the upper end of said pipe, means for drawing a vacuum at said outlet opening, and means providing an enlarged opening at the lower end of said pipe, said opening having a larger diameter than said pipe, but no greater than the diameter of said bit.

2. Apparatus for air drilling large diameter holes comprising a drill stem having a large diameter bit attached to its lower end, means for imparting a cutting action to said bit, a bore extending through said drill stem and having at least one opening at the location of said bit, means for introducing air under pressure into said bore, a pipe surrounding said drill stem, means providing an outlet opening near the upper end of said pipe, means for drawing a vacuum at said outlet opening, and means providing an enlarged opening at the lower end of said pipe, said opening having a larger diameter than said pipe, but no greater than the diameter of said bit.

3. Apparatus for air drilling large diameter holes comprising a drill stem having a large diameter bit attached to its lower end, means for imparting vertical reciprocatory movement to said bit, a bore extending through said drill stem and having at least one opening at the location of said bit, means for introducing air under pressure into said bore, a non-rotating pipe surrounding said drill stem, means providing an outlet opening near the upper end of said pipe, means for drawing a vacuum at said outlet opening, and means providing an enlarged opening at the lower end of said pipe, said opening having a larger diameter than said pipe, but no greater than the diameter of said bit.

4. Apparatus for air drilling large diameter holes comprising a drill stem having a large diameter bit attached to its lower end, means for imparting rotational movement tO said bit, a bore extending through said drill stem and having at least one opening at the location of said bit, means for introducing air under pressure into said bore, air-powered reciprocating means receiving air from within said bore for imparting a hammering action to said bit, a non-rotating pipe surrounding said drill stem, an outlet opening near the upper end of said pipe, means for drawing a vacuum at said outlet opening, and means providing an enlarged opening at the lower end of said pipe, said opening having a larger diameter than said pipe, but no greater that the diameter of said bit.

5. Apparatus for air drilling large diameter holes comprising a drill stem having a large diameter bit attached to its lower end, means for imparting rotational movement to said bit, a bore extending through said drill stem, at least one opening at the location of said bit, means for introducing air under pressure into said bore, air-powered reciprocating means receiving air from within said bore for imparting a hammering action to said bit, means for discharging air exhausted from said reciprocating means through said opening, a non-rotating pipe surrounding said drill stem, an outlet opening near the upper end of said pipe, means for drawing a vacuum at said outlet opening, and means providing an enlarged opening at the lower end of said pipe, said opening having a larger diameter than said pipe, but no greater than the diameter of said bit.

6. Apparatus for air drilling large diameter holes comprising a rotatable drill stem having a large diameter bit attached to its lower end, means for imparting rotational movement to said bit, a bore extending through said drill stem and having at least one opening at the location of said bit, means for introducing air under pressure into said bore, a non-rotating pipe surrounding said drill stem, means providing a seal between said pipe and said stem at the upper end of said pipe, an outlet opening near the upper end of said pipe, means for drawing a vacuum at said outlet opening, and an opening at the lower end of said pipe for collecting air and cuttings from the bottom of a hole being drilled.

7. Apparatus for air drilling large diameter holes comprising a rotatable drill stem having a large diameter bit attached to its lower end, means for imparting rotational movement to said drill stem, a bore extending through said drill stem and having at least one opening at the location of said bit, means for introducing air under pressure into said bore, a non-rotating pipe surrounding said drill stem, means providing an outlet opening near the upper end of said pipe, means for drawing a vacuum at said outlet opening, and an opening at the lower end of said pipe for collecting air and cuttings from the bottom of a hole being drilled, said non-rotating pipe comprising a plurality of sections arranged in end-to-end relation, and means for fastening said sections together.

8. Apparatus according to claim 7 in which said drill stem comprises a plurality of drill stem sections arranged in end-to-end relationship and means for fastening said drill stem section together.

9. Apparatus for air drilling large diameter holes comprising a rotatable drill stem having a large diameter bit attached to its lower end, means for imparting rotational movement to said drill stem, a bore extending through said drill stem and having at least one opening at the location of said bit, means for introducing air under pressure into said bore, a non-rotating pipe surrounding said drill stem, means providing an outlet opening near the upper end of said pipe, means for drawing a vacuum at said outlet opening, and an opening at the lower end of said pipe for collecting air and cuttings from the bottom of a hole being drilled, said non-rotating pipe comprising a plurality of sections connecTed in end-to-end relation, and means at each connection for fastening said sections together, each said fastening means comprising a flange fastened to the end of one of said sections, a flange fastened to the end of the other section at said connection, and means for fastening said flange in face to face relationship, at least one of said flanges having attached to it spider means having a central opening through which said drill stem extends, said spider means providing at least one opening between said drill stem and said pipe for the passage of air and cuttings upwardly to said outlet opening near the upper end of said pipe.

11. Apparatus according to claim 9 in which said drill stem comprises a plurality of drill stem sections arranged in end-to-end relationship and means for fastening said drill stem section together.

12. Apparatus for air drilling large diameter holes comprising a drill stem having a large diameter bit attached to its lower end, means for imparting a cutting action to said bit, a bore extending through said drill stem and having at least one opening at the location of said bit, means for introducing air under pressure into said bore, a pipe surrounding said drill stem, means providing an outlet opening near the upper end of said pipe, means for drawing a vacuum at said outlet opening, means providing an opening at the lower end of said pipe, and shielding means fastened to the lower end of said pipe for preventing dust produced by the cutting action of said bit from passing upwardly to the surface through the space between the pipe and the wall of the hole being drilled.

13. Apparatus according to claim 12 including a skirt having a maximum diameter not exceeding that of said bit and means detachably fastening said skirt to the shielding means.

14. Apparatus for air drilling large diameter holes comprising a drill stem having a large diameter bit attached to its lower end. means for imparting a cutting action to said bit, a bore extending through said drill stem and having at least one opening at the location of said bit, means for introducing air under pressure into said bore, a pipe surrounding said drill stem, an opening at the lower end of said pipe for collecting air and cuttings from the bottom of a hole being drilled, a collection box for cuttings, said box having an inlet opening, an outlet opening and at least one baffle obstructing a straight path between said inlet and outlet openings, means providing an opening near the upper end of said pipe, means for drawing a vacuum, a conduit connecting said opening near the upper end of said pipe to the inlet opening of said collection box, and means connecting said means for drawing a vacuum to the outlet opening of said collection box.

16. Apparatus according to claim 14 including shielding means fastened to the lower end of said pipe for preventing dust produced by the cutting action of said bit from passing upwardly to the surface through the space between the pipe and the wall of the hole being drilled.