CA1166857A - Apparatus and method for coring subterranean holes - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

There is described a method and apparatus for non-rotatively forming holes in the ground between first and second spaced locations, the apparatus comprising a pilot hole forming head for forming a pilot hole between the first and second spaced locations, a broaching head having a first trailing end and a second leading end for cutting a core of earth, core extruders cooperating with the broaching head to extrude the core of earth, and winches respectively connected to the leading end of the broaching head for pulling the broaching head along the pilot hole towards the second location to cut the core of earth and to the trailing end of the broaching head to pull the broaching head towards the first location to extrude the core of earth.

Description

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The present invention relates to an earth boring app~-ratus and method and more particularly to an apparatus and method for nonrotatively forming substantially horizontal holes of various sizes between two spaced apart locations.
Earth boring apparatus of the present type find appli-cation in the installation o~ pipes, conduits, cables or virtual-ly any other type of underground transmission medium normally layed in a trench dug in the ground~ When laying such trans-mission media over any distance, surface installations such as roads, driveways, bridges or railines to name but a few are usually encountered. To avoid disruption of these installations and the expense of broaching them to lay the line, it has proven desirable and indeed necessary in certain cases to be able to bore a hole of adequate size beneath the surface installation to receive the transmission line. Typically, a trench or operat-ing pit is dug on either side of the surface installation, the pit being of an adequate size to receive the necessary boring apparatus at either end of the hole. A pilot hole or coring apparatus is then "shot" from one pit to the other to be in alignment with the incoming transmission line, which will, for the purpose of illustration, be hereinafter referred to as a pipe.
A typical method and apparatus by which such boring has been accomplished to date is illustrated in Canadian patents 760,~41, 773,006 and 779,148 to Atkins et. alO which issued in 1967.
Atkins teaches an apparatus and a four step procedure for forming the bore holes. Firstly, a pilot hole is shot from one trench to the other using a pilot hole cutter. Power is supplied by means of an hydraulic power head or pusher situate ,~

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in one trench. The pilot hole is then expanded by pushing spherical expanders having diameters greater than that of the cutter throuyh the hole to compress the surrounding soilO Once through, the pilot hole cutter and expanders are remo~ed and an earth cutter is affixed to the end of the rod string. The earth cutter is then drawn back, being guided by the pilot hole, to incise a core of earth. The direction and movement of the cutter is then reversed, that is, it is pushed back towards the end of the hole to extrude the core. A relatively small down-turned flange on the trailing edge of the cutter is intended to score the surface of the core to reduce friction between it and the surrounding wall and to grip the core when the earth cutter is pushed back for the purpose of extruding the core.
It will be apparent to those skilled in the art that this manner of forming bore holes suffers ~rom a number of disadvantages. For on~, a multiplicity of steps is required, adding complexity, prolonying the operation and increasing the wear and tear on the machinery and hence increasin~ the risk that breakdowns or problems will be encountered. A
prolonged procedure also results in increased costs.
An improved method and apparatus for forming sub-terranean holes between s~aced apart locations has been described in my Canadian Patent No. 1,106,833 issued on the 11th of August, 1981 wherein there is described a method of using an hydraulic ram to push a broaching head or knife through the ground to cut a core of earth, reversing the orientation of the knife upon emergence into the second pit and pulling the knife partially back along the core so cut and then reversing the thrust to the knife which includes cooperating e~truding means to extrude the core of earth cut by the knife. The method and apparatus described in i :~B68~

Canadian Patent 1,106,833 is particularly suited for difficult soil conditions and for the formation of holes over lon~ distances.
It will be appreciated that the above described methods of forming subterranian holes involve the use of hydraulic rams which push sections of rod connected to the various cutting or enlarging tools through the ground and then pull the rods and any tools a~fixed thereto rearwardly for the purposes of core extrusion or hole enlargement. The rods themselves are typically five feet long and are screw threaded one to the other.
As the rods are being pushed through the ground for instance, it is necessary to periodically pause to connect another length of rod to the preceding length until the cutting tool or pilot hole forming head emerges into the second operating pit. If the operating pits are spaced at typical distances ranging from forty-five to one hundred feet~ anywhere from eight to nineteen work interruptions are required for the purpose of connecting one rod section to another. Similarly, when retracting the rods, or particularl~ when moving the knie back and forth to extrude segments of the core, the time re~uired to connect and disconnect rod sections consumes a disproportionate share of the entire amount of time re~uired to bore the hole.
Accordingly, where soil and coring conditions permit, there is a need for an improved method and apparatus fox forming subterranian holes which substantiall~ eliminates the need to connect and disconnect sections of rod during the core cutting and core extruding phases of the operation.
According to the present invenkion, then, there is provided an apparatus for non-rotatively forming holes in the ground between first and second spaced apart locations com-~ :~66~.5~

prising pilot hole ~orming means ~or forming a pllot hole betweensaid first and second spaced apart ].ocations, broaching means having a first trailing end and a second leading end for cutting a core of earth, extruding means cooperatin~ with said broaching means to extrude said core of earth and pulling means connected to the leading end of said broaching means for pulling said broaching means along said pilot hole towards said second spaced location to cut said core of earth and connected to said trailing end of the broaching means for pulling sald broaching means towards said first spaced apart locations to extrude said core of earth.
According to another aspect of the present in~ention, there is provided a method for non-rotatively forming holes in the ground between first and second spaced apart locations including the steps of forming a pilot hole between said first and second spaced apart locationsl alternately pushing a broach ing head having a trailing and a leading end along said pilot hole towards said second spaced apart location to cut a core of earth, said pulling being by means of pulling means releas-ably connectable to said leading end, and pulling said broachinghead also having core extruding means cooperating therewith towards said first spaced apart location to extrude said core of earth, said pulling being by means of pulling means releas-ably connectable to said trailing end of said broaching means until said hole is formed.
Embodiments of the present invention will now be des-cribed in greater detail and will be better understood when read in conjunction with the accompanying drawings in which:
Figure 1 to 4 illustrate the formation of a bore hole in a manner to be described herein;

Figure 5 schematically illustrates an alternative to the method of Figure 1 for forming a pilot hole;
Figure 6 is a side elevational view illustrating the pilot hole forming assembly schematically illustrated in Figure 5;
Figure 7 is a partially sectional, side elevational view of the broaching head for use with the apparatus of Figures l to 4;
Figure 8 is a partially sectional, side elevational view of a modified broaching head for use with the apparatus of Figures 1 to 4;
Figure 9 is a front elevational view of the broaching head of Figure 7;
Figure 10 is a side elevational view of another embodiment of the broaching head of Figure 7;
Figure ll is a front elevational view of the broaching head of Figure 10;
Figure 12 is a schematic cross sectional view taken along line A-A of Figure 11 of a gate mech~nism a~flxed to the broaching head of Figure 8;
Figure 13 is a plan view of an alternative gate mechanism;
Figure 14 is a sectional view of the gate mechanism of Figure 13 taken along line A-A thereof;
Figure 15 illustrates an alternative method of forming a bore hole in a manner to be described hereinbelow.
Referring now to Figures l to 4, there is illustrated an earth coring procedure according to an embodiment of the present invention. Operating trenches or pits 5 and 6 are formed on either side of a surface installation (not shown) such as a road. Into pit 5 i5 placed a pusher 2 of any suitable type although very good results are obtained using a hydraulic apparatus. Such apparatus are well known and form no part o~ the present invention. Accordingly, no further description of the power head need be provided here. The hydraulic pump actuating pusher 2 may be mounted on a truck with merely the hydraulic lines being led to the pusher in the pit. The pusher actuates a string of rods 3, each typically about 5 feet long, connected at their leading end to a pilot hole forming head 7. (For clarity, the diameter of forming head 7 has been exaggerated.) A winch 15, preferably hydraulically actuated as well, is situated in pit 6.
When power is applied, pilot hole forming head 7 is pushed through the ground in the direction of arrow A towards pit 6 to form a pilot hole 10. Pilot hole forming head 7 may be of any known configuration such that further details ~hereof need not be provided here. It has been found, however, that those types of pilot hole forming heads having a ~lat or concave face demonstrate the greatest tendency to remain on a true and straight course between pits 5 and 6 and to resist the deflecting forces exerted by minor obstacles such as small stones and differential soil pressures.
Upon the emergence of head 7 into pit 6, the formation of pilot hole 10 is complete whereupon rods 3, with or without pilot hole ~orming head 7 attached thereto, are withdrawn by pusher 2 back towards pit 5. As the rods are withdrawn, they are disconnected from each other one by one until completely removed from the pilot hole. A cable 12 emanating from winch 15 is affixed to either the end of rod string 3 or to pilot hole forming head 7 as the rods are withdrawn so that cable 12 is pulled towards and then into pit 5.
To facilitate the pulling of ca~le 12, pilot hole forming head 7 may be removed and a threaded eyelet (not shown) of any suitable configuration may be attached to the end of rod string 3. Cable 12 may then be readily attached to the eyelet in any suitable fashion such as by using a safety hook.
Upon retrieval of the rod sectionsl pusher 2 is removed from pit 5 and is replaced by a second hydraulic winch 14 which is positioned towards the rear of pit 5 opposite the point of emergence of pilot hole 10.
A broaching head 20, also referred to hereinafter as a knife, is connected to winch 15 via cable 12 and to winch 14 via cable 13. Winches 14 and 15 may be of any known commerci.ally available configuration and will therefore not be described in detail here. ~s winch 15 reels in cable 12, knife 20 is drawn towards pit 6 to cut a core of earth 30. It will be appreciated that the diameter of pilot hole 10 should exceed the diameter of cables 12 and 13 to avoid frictional drag between the cables and the surrounding walls of the pilot hole.
Winch lS may be utilized to pull knife 20 approximately five to ten feet, depending upon soil conditions, towards pit 6. Winch 15 is then deactivated and allowed to freewheel as winch 14 pulls knife 20 back towards pit 5 for the purpose of extruding core 30 in a manner to be descrihed below. Re~erence is particularly made to Figure 4 which illustrates the core extruding process and which shows knife 20 being drawn in the direction indicated by arrow C. The extruded core of earth accumulates in pit 5 at the foot of winch 14 and may be moved aside by any suitable manual or mechanical means. Upon extrusion of the first segment of core 30, winch 14 is allowed to freewheel as winch 15 pulls knife 20 an additional 5 to 10 feet along the pilot hole towards pit 6. Winch 15 is then deactivated and winch 14 is used to withdraw the knife to remove or extrude the next segment of core 30. This process is repeated until a bore hole 31 has been formed between pits 5 and 6. It will be understood that under some soil operating conditions, such as when cutting highly viscous or heavy clays, it may be desirable to cut only 3 to 5 feet of core at a time whereas in ot~er soils of less consistency, it may be possible to extrude core segments greater than 10 feet in length.
It will be appreciated that the back and forth winching operation described above completely eliminates the need to continuously connect and disconnect lengths of rod such as initially used to form the pilot hole duxing the core cutting and extruding processes. Substantial amounts of time can thus be saved and it has been found in practice that the amount of time required to core a hole using the present method and apparatus can be reduced by a factor of 10 under good coring conditions.
An alternative method of forming a pilot hole and a tool adapted for this purpose are illustrated in Figures 5 and 6.
In place of the pilot hole forming head 7, there may be substituted an integral tool 11 basically comprising a relatively small knife 61 and a guide 62 disposed about a central shaft 60. Guide 62 includes a plurality of radiating fins 75 to provide a greater degree of directional stability when shooting tool 11 ~sometimes hereinafter referred to as a bazooka) between pits 5 and 6. Knife 61 is constructed in a manner similar to knife 20 as will be more fully described below.
The function of knife 61 is to cut a small core of earth about rod 60 and rod string 3 to thereby reduce frictional drag between the rods and the walls surrounding the small core.
With particular regard to ~igure 6, bazooka 11 includes, as aforesaid, a knife 61 and a guide 62 formed about shaft 60. A cap 63 is fitted about the leading end of shaft 60, it having been found that good directional stability is obtained using a cap having either a ~lat or a concavely curved leading surface. A threaded connector 64 is fitted into the trailing end of the shaft for connection to rod string 3. The basic construction of knife 61 is subs~antially identical to knife 20 described below with reference to Figure 7. Knife 61 may comprise a hollow central shaft 67 which fits concentrically about shaft 60 for secure attachment thereto. As is well known in the art, however, it is often desirable to turn rods 3 by ~ to ~ a turn with the insertion of each 5 to 10 feet of rod into the ground.
To facilitate this technique, shaft 67 may alternatively be slidably received about rod 60 to be freely rotatable thereabout.
The trailing peripheral vane 71 of knife 61 may be smaller in diameter than the leading peripheral vane and may be tapered rearwardly to compress the core during the cutting thereof.
Guide 62 is typically also rotatable about rod 60.
Guide 62 may be made rotatable about rod 60 in a number of ways. By way of example only, a section of tubing 68 equal in diameter to shaft 60, is rotatably fitted about a spindle member 69,the ends of which project beyond the limits of tube 68. The projecting ends of the spindle are received into the adjacent ends of shaft 60. The spindle is fixedly held in place by pins 70 or any other suitable method including welds. In a preferred embodiment constructed by the applicant, the length of tool 11 is approximately five feet, the diameter of rod 60 is 1~ to 2 inches and the diameter of knife 61 is 4~ inches.
It will be understood that bazooka 11 less knife 61 may also be used to form the pilot hole.

A more complete description of bazooka 11 is to be found in my Canadian Patent No. 1,106,833.
Referring now to Figure 7, broaching head 20 comprises a central rigid shaft 16 adapted at both ends 17 and 13 thereof for attac~ment to cables 12 and 13. The ends may either be provided with eyelets as shown in Figure 7 for connection to safety hooks (not shown~ affixed to the ends of cables 12 or 13 or adapted in any other suitable manner for releasable connection to the cables.
Radiating outwardly from shaft 16 are a plurality of vanes 25 which may be welded to the shaft. Any num~er of radial vanes 25 may be provided but it will be appreciated that the greater number of vanes, the greater will be the power requirements necessary to pull the knife through the yround.
It has been found that the provision of 3 or 4 vanes 25 affords an optimal combination of strength versus pull resistance. Each of vanes 25 is attached proximal to end 17 of shaft 16 and projects therefrom radlally outwardly and rearwardly towards end 18 to a point of connection to the leading edge 22 of peripheral vane 21. Vanes 25 then continue rearwardly in a direction parallel to shaft 16 until they emerge at the trailing edge of vane 21, from which point the outer edges of vanes 25 taper inwardly towards shaft 16 to a point of connection with leading edge 24 of peripheral vane 23. This inward tapering of the vanes is due to the fact that the diameter of vane 21 exceeds that of vane 23. From this poin-t, vanes 25 continue to extend towards end 18, terminating at the trailing edge of vane 23. Radial I ~;8~.5~

vanes 25 thus define p]anar surEaces connecte~ to and supportiny peripheral vanes 21 and 23. L~ading edges 22 and 24 of vanes 21 and 23 respectively, and the leading edges 26 of vanes 25 may be bevelled to define sharpened cutting edges to facilitate the passage of knife 20 through the ground.
Pilot hole 10 may be formed to have a diameter in excess of that of either eyelet 17 or shaft 16 to thereby mini-mize the frictional resistance of the ground a~ainst the passage of knife 20.
With particular regard to Figure 9, peripheral vanes 21 and 23 are illustrated as being hexagonal in shape although the actual shape may be varied to include cylinders, squares or other appropriate shapes as may be necessary to form the shape and size of bore hole required. It has been found that for the boring of holes having diameters of 5 inches or less, a hexagonally shaped knife provides good results, whereas for bore holes in excess of five inches in diameter, the dodecahedral shape illustrated in Figures 10 & 11 offers good results. Circu-lar knives have also proven effective in coring holes of all diameters. It will be appreciated that the a~tual diameter of knife 20 will be chosen depending upon the re~uirements of the job at hand.
Because the diameter of vane 21 is greater than that of vane 23, two concentric cuts will be formed, one slightly larger than the other. In the embodiment illustrated in Figures 9 and ll~the outer surface of vane 23 is coplanar with the inner suxface of vane 21. Accordingly, a layer of soil of a thickness approximately equal to the thickness of vanes 21 and 23 together will be displaced or squeezed from around core 30 by the action of the vanes. Core 30 is then spaced from the wall of bore 3 ~68~

31 and friction therebetween is subs~antia~ly re~uced, thereby facilitating the extrusion of the core.
It is also contemplated that the spacing of the vanes 21 and 23 from shaft 16 may be such that the inner and outer surfaces thereof, respectively, are not coplanar but are spaced apart. Soil passing between the vanes will be squeezed or otherwise displaced to again result in the formation of either a space between core 30 and the surrounding walls or an annulus of soil therebetween, again having the effect of facilitating th~ extrusion of the core and lessening the compressive forces otherwise exerted on the core itself and on the apparatus.
It is further contemplated that vane 23 may be inclined slightly towards end 18 of shaft 1~ as shown in broken lines in Fiaure 7. As the core passes through vane 23, it is com-pressed to reduce its diameter somewhat so that there is less friction to overcome when extruding the core. Good results have been obtained by tapering vane 23 by 1/4 to 1/2 of an inch from front to back.
With reference to Figure ~, kni~e 20 may be advan-tageously modified to include a shaft 16 of extended length.By way of example only, shaft 16 may be 30 inches long so as to extend approximately 10 inches in either direction beyond the usual ends of the knife. In this regard, the extended ends of shaft 16 project approximately equally beyond each end of the knife. In the~embodiment of Figure 8, shaft 16 is shown as comprising a single length of rod. It will be understood, however, that shaft 16 as it appears in Figure 7 may be adapted at its opposite ends to threadably receive additional lengths of rod to produce the required extension. This method offers the advantage that should the extensions become bent or broken, they may be easily replaced without replacing the knife as a whole.

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Extended ro~ 16 is of course initially gui~ed along the pilot hole during the formation of core 31. It therefore acts as a stabilizer to prevent or at least hinder knife 20 from deflecting excessively should the blades of the knife encounter small obstacles such as rocks or roots in the soil.
Rod 16 is closely confined within the pilot hole, limiting its ability to pivot and therefore limiting the ability of the knife as a whole to pivot upon encountering an obstacle.
When knife 20 is pulled through an existing hole, such as would be the case if successively larger knifes are being used to form a hole having a relatively large diameter, the leading end of the rod including eyelet 17 will be positioned well past the point of contact between the obstruction and a blade or vane of the knife to provide, in cooperation with the pulling action of cable 12, improved leverage when pulling the knife past the obstruction, thereby preventing or otherwise minimizing possible deflection of the knife.
When pu~ling knife 20 towards pit 5 to extrude a core, the rearward extension of rod 16 is similarly useful to prevent further deflections should the knife re-encounter any peripherally extending obstructions and to guiae the knife along the hole and to minimize its tendency to shave or ni~bble at the walls of the hole.
Referring to the embodiments illustrated in Figures 9 and 12 together, three radial vanes 25 are spaced at equidis-tant intervals about shaft 16 to define an angle of 120 between each adjacent pair of vanes. Provided on each of vanes 25 at a point intermediate shaft 16 and peripheral vane 23 is a gate assembly 27 comprising a swingable gate 28 pivotably mounted on a wedge shaped mount 29 by means of a hinge pin ~ ~ 6 6 8 .~ ~

26 rotatably received in mount 29. Alternatively, gate 28 may be pivotably mounted about hinge pin 26 with the latter fixedly received in mount 29.
In operation, gate 28 is disposed to open, as is illustrated by the solid lines in Figure 12, as knife 20 is pulled in the direction indicated by the arrow mar~ed E. This allows for the passage of soil through the knife without e~cessive resistance.
When the broaching head is pulled in the direction indicated by arrow F in Figure 12, the gates catch the soil and are pivoted into the closed position illustrated by the phantom lines in Figure 12. The gate is held in this position by the action of gate stop 32 integrally formed with mount 29. Depending upon the size of the gate, then, the open spaces 33 defined between adjacent pairs of vanes 25 and peripheral vane 23 are either wholly or partially closed up such that as knife 20 is pulled towards pit 5, it acts as a ram to extrude the core as illustrated in Figure 4, biting off a piece of the core if necessary.
With reference to Figures 13 and 14, there is illustrated an alternative method of mounting ~he gates which considerably reduces the exposed profiles thereof and, corres-pondingly, their frictional resistance to movement through the ground. A T-shaped opening or slot 52 is formed into the trailing end of radial vanes 25. A hinge plate 53 having a hinge pin socket 54 formed at one end thereof is securely fixed to vane 25 adjacent the wide end of slot 52 so that socket 54 projects into the slot. Gate 55 is then pivotably mounted to hinge plate 53 by means of a hinge pin 56 rotatably received - 14 ~

into socket 54. Accordingly~ gate 55 will project outwardly and rearwardly from slot 52 to present a very limited profile when knife 20 is being pulled in the direction denoted by arrow F in Figure 14. Of course, when the direction of movement is reversed, such as, for instance, when the knife ~s pulled towards pit 5 by means of winch 14, the outwardly projecting end of gate 55 will catch the soil and be pivoted into the closed position thereof as denoted by ~he phantom lines in Figure 14.
It will be apparent to those skilled in the art that other means of mounting gates to ~anes 25 may be adopted without departing from the inventive concept described herein.
If plug 30 is composed of heavy, viscous or otherwise difficult to replace soils such as clay, it will be desirable to form the gates to close up only a relatively small portion of space 33.
In the event that very large bore holes are required~
successively larger knives 20 can be u~ed until the desired size of bore is attained.
It will be appreciated that other means o~ extruding the core are contemplated. ~y way of example only, knife 20 may be formed without gates disposed on peripheral vanes 21 or 23 but may include a third peripheral vane disposed either forwardly or rearwardly of knife 20 but connected thereto and having the gates affixed thereon.
Knife 20 can be fabricated from any suitable material such as high strength steel.
Referring now to Figure 15, there is illustrated an alternative method of coring which employs a single surface mounted winch 75 rather than two winches 14 and 15 disposed within pits 5 and 6, respectivelyO Winch 75 i5 provided with two spools ~not shown) one of which is wound in a clockwise as~

direction and the other of which is wound in a counterclockwise direction. Accordingly, cable 12 reels out while cable 13 is being wound in to pull, for example, knife 20 towards pit 6. Of course, the reverse is true when cable 12 is being reeled in to pull knife 20 towards pit 5 to extrude core 30, for example. Frames 80 include sheaves 70 mounted thereon to guide cables 12 and 13 from winch 75 to opposite ends of knife 20. Frames 80 may be of any suitable construction so as to rigidl~ support the sheaves against,the reactive forces exerted by the tension in cables 12 and 13.

Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An apparatus for non-rotatively forming holes in the ground between first and second spaced locations compris-ing:
pilot hole forming means for forming a pilot hole between said first and second spaced locations;
broaching means having a first trailing end and a second leading end for cutting a core of earth;
extruding means cooperating with said broaching means to extrude said core of earth; and pulling means connected to the leading end of said broaching means for pulling said broaching means along said pilot hole towards said second location to cut said core of earth and connected to said trailing end of the broaching means for pulling said broaching means towards said first location to extrude said core of earth.

2. The apparatus of claim 1 wherein said pulling means comprise first and second winch means disposed at said first and second spaced locations, respectively, said first and second winch means including cable means extending there-from for releasable connection to said leading and trailing ends of said broaching means, respectively.

3. The apparatus of claim 2 wherein said broaching means comprise a central member adapted at each thereof for attachment to said cable means, first and second peripheral vanes circumferentially disposed about said central member, said first vane being located forwardly relatively to said second vane when said broaching means are being pulled towards said second spaced location, the diameter of said first vane being larger than that of said second vane, and a plurality of radial vanes extending between said central member and said peripheral vanes to support said peripheral vanes and to radial-ly cut said core of earth as said broaching means are pulled through the ground.

4. The apparatus of claim 3 wherein said extruding means comprise gate means mounted on said radial vanes, said gate means being adapted to open during the pulling of said broaching means through the ground towards said second spaced location and to close during the pulling of said broaching means towards said first spaced location, whereupon said gate means close at least part of an area defined between adjacent pairs of radial vanes and said peripheral vane to facilitate the extru-sion of said core of earth.

5. The apparatus of claim 4 wherein said second peri-pheral vane is tapered towards said trailing end of said broach-ing means.

6. The apparatus of claim 1 wherein said pulling means comprise winch means having cable means extending in oppo-site directions therefrom for releasable connection to said leading and trailing ends of said broaching means such that said winch means are effective to alternately pull said broaching means towards said first or second spaced locations.

7. The apparatus of claims 3, 4 or 5 wherein said central member is extended in length to project forwardly and rearwardly of said broaching means along the longitudinal axis thereof.

8. A method for non-rotatively forming holes in the ground between first and second spaced locations including the steps of:
forming a pilot hole between said first and second spaced locations;
alternately pulling broaching means having a trailing and a leading end along said pilot hole towards said second location to cut a core of earth, said pulling being by means of pulling means connected to the leading end of said broaching means; and then pulling said broaching means having core extruding means cooperating therewith towards said first location to extrude said core of earth, said pulling being by means of pulling means releasably connected to said trailing end of said broaching means.

9. The method of claim 8 including the step of compacting the core during the cutting thereof.

10. The method of claim 9 wherein the step of extruding said core includes the step of pulling said broaching means towards said first spaced location, whereupon the broaching means is utilized to extrude said core to form the hole by at least partially closing said broaching means to prevent the passage of the core therethrough.

11. The method of claim 10 wherein said core is cut by forming said first and second coaxial incisions whereby subsequent removal of the core is facilitated.