NZ201517A - Ground drillhead with radial offset compensator - Google Patents

Description

201517 Priority Dete(s): -.S | CompJet© Specification filed: ctass: Publication Date: P.Ef, (MJ P.O. Journal. No: .. l&Jft.

Patents Form No.5 .6 AUG 1982 w RKBV^d NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION "DRILLING DEVICE" T",WE ENGTECH S.A. a Swiss Body Corporate of 1, rue de Fries - 17 00 Fribourg/Switzerland, hereby declare the invention, for which-t/we pray that a patent may be granted to me/us, ,and the method by which it is to be performed, to be particularly described in and by the following statement:- 201517 The present invention concerns a drilling device comprising a drilling head equipped with a rotating body through which runs a duct for supplying air and water or other, drilling fluid and bearing at least one rotating cutting element.

Existing drilling devices comprising a drilling head equipped with three cutting elements markedly conical or in the shape of a truncated cone have been known and 10 used since the 'thirties. The three theoretical tops of the cutting elements coincide with a point of the rotating shaft of the drilling head. The side of each cone is fitted with teeth of a size and sharpness appropriate to the type of ground to be drilled; Each cone is mounted on the drilling head in such a way that it rests on the ground following one of its generants and the teeth of one cone fit into the spaces between the teeth of the adjacent cone. The action of the three cones on the ground is the same as that of three rollers fitted with 20 teeth. Each cone is retained radially by a shaft on which 2 201517 is mounted a ball bearing retaining the cone axially.

During drilling, especially in the case of rocky ground, great pressure must be exerted to break the rock and subsequently cut it up and clear it away. With the three 5 cones working along one of their generants, the working surface is large and great weight must be brought to bear on the drilling head to obtain the necessary pressure. The ground undergoes great compression which has the effect of breaking the rock, especially in the case of 10 a rock cracked, over a radially more extensive surface than that of the drilling, thus creating an irregular drilling profile and an unstable wall.

The continuous injection of any drilling fluid into the bottom of the hole ensures the evacuation of the 15 execavated ground and rock cut up by the three cones.

The diameter of the surface of the bottom of the hole is approximately the same as the diameter of the drilling head and the evacuation of excavated ground and rock is only ensured if the dimensions of the excavated rock allow them 20 to pass between the periphery of the head and the wall of the hole. The pieces of rock must therefore be broken up until they can pass between the wall of the hole and the periphery of the drilling head, slowing up the progress of the drilling and allowing fine particles of the excavated 25 rock conveyed by the drilling fluid to reach the drill bit bearings, so destroying them.

Replacing a cone in case of breakdown takes a long _o\\time because the bearing must be removed to take off the cone. >rVu The construction of a drilling head equipped with a hemisphere shaped disc fixed to a shaft almost perpendicular to the axis of the rotating body has already been suggested. ho The circumf erence of the hemisphere shaped disc is fi?t§<|-with means to cut and profile the wall while the spherical surface which rests against the bottom of the hole to break by compression the bottom and the pieces cut out by the edge of the disc.

The invention aims to make it possible to produce a drilling device operating at low power, the cutting element being easily mounted on the drilling head and enabling the evacuation of large pieces of debris.

The drilling device according to the invention is characterized by the fact that the cutting element is a disc provided with at least an annular cutting part and that the rotating body carries, on the side opposite to that carrying the rotating support of the disc, at least one counter-reacting element and placed so that the said element contacts a wall of the hole being drilled to centre the drilling head by compensating for the radial component of the reaction of the wall on the disc and to compact and strengthen the wall.

The counter-reacting element serves to stabilize the drilling head which could tend to oscillate around the drill shaft axis and to slightly offset the lower point of the cutting surface in relation to the drilling axis.

Because the disc acts on the ground to be cut by an annular surface equipped with cutting means, the action of the disc is to shear the ground and not to compress it in order to obtain its disintegration. There is certainly a slight compression by the disc at the very bottom of the hole but it is not essential to the working of the device. Moreover, the counter-reacting element resting against the opposite side of the wall allows for centering of the tool and compensates for the radial reaction of the disc against the ground being cut, which has' a tendency to resist disc. The power needed for drilling is relatively low,the drilling being achieved by shearing and not by compression. In this way, a more stable wall is obtained. Because the wall is less likely to give way than when using a conventional drilling head, the cost of installing tubes to prevent the wall from collapsing can be reduced. The cutting disc rests only on part of the hole bottom, less than half, leaving ample space for the evacuation of large pieces of excavated rock.

According to another version, and for those cases when it is essential to use tubes to support the wall of the drilled hole, the rotating support of the disc is mounted on a hinged arm so that the drilling head can be inserted or removed through the tubes. The movement of the hinge is around an axis perpendicular to the rotating axis of the drilling head. In order to insert or remove the drilling head through the tubes, the rotating support of the cutting disc is moved, by pivoting the hinged arm, to a position forming an extension of the axis of rotation of the drilling head, the internal diameter of the tubes being greater than that of the disc. Resiliant means bias the rotating support of the disc into an inclined position after the drilling head has passed through the tubes. This device enables the drilling head to be removed for repairs or sharpening without having to remove the tubing, which would cause the wall to collapse, partially blocking the hole. This device also enables the cutting disc to be changed if, at a certain depth, the type of ground changes, going, for instance, from a layer of sand to a much harder - \ §rlayer. In this way, time is saved. In this case, the counter-reacting element is mounted on a radially extensible arm. 20151.7 According to another version, the drilling head is equipped with at least two cutting discs placed alternately on either side at regular intervals along the rotating body.

Since the head is mostly used to enlarge the diamater of a previously drilled hole, the dimensions of a cutting disc and/or the length of its rotating element are greater than those of the preceding disc and smaller than those of the following disc, going from the lower end to the upper end of the rotating body. Finally, in the case of enlargement of the diameter of the hole, a lower drilling device may be provided which serves only as a guide can be a conventional drill-bit. The cutting surface of the disc can be approximately the shape of a truncated cone or a ring cut in a spherical surface.

According to another variation in design, the cutting disc is rotated independently of the main shaft, thus increasing its cutting effect which makes it possible both to speed up the drilling work and to diminish further the pressure exerted in the drilling direction.

According to a variation, the compensating element is a roller having an elliptical section perpendicular to the drilling axis. The advantage of this roller, which actually does not continually roll but rubs against the cut wall, is that it permits automatic centering of the drilling head even in places where the wall of the hole is cut into more deeply due to the instability of the ground or because a large piece of rock is cut out. In fact, in normal conditions the roller rubs against the wall with part of its side surface perpendicular to the small axis of the ellipse^y ° - 6 - C"30CTi98$ 201517 and that wheh tfce roller, because of an irregularity in the wall, is no longer in contact with the wall, the drilling head is put off centre under the effect of the reaction of the wall on the cutting disc until the roller again comes into contact with the wall and at that time will re-centre the drilling head by rolling on its side surface and pushing the disc against the wall. Of course, the depth of the irregularity should not be greater than half the difference in length between the small arid large axes of the ellipse. The movement of the roller is less than 90°. As soon as the disc comes into contact with the wall, the roller no longer rolls but merely rubs against the wall with a part of its side surface which is further away from the roller spindle than the part without any irregularity in the wall.

Preferably the roller is made from flexible material and its side surface in a hard material. A roller with circular section mounted on a radially extensible arm can be used.

According to a preferred version, the counter-reacting element is a simple friction surface mounted on a projection.

The attached drawings show, as examples, five different versions of the invention.

Figure 1 is a longitudinal section of one version.

Figure 2 shows the same version as Figure 1, the cutting disc and the roller being different.

Figure 3 is a longitudinal section of a hinged device.

Figure 4 is a view in plan of the lower part of the preceding Figure. 7 201517 Figure 5 is a longitudinal section of the device shown in Figure 3 in the retracted position.

- Figure 6 is a schematic view of a drilling head designed to enlarge an existing boring/drilling.

Figure 7 is a diagram showing a longitudinal section and profile of a drilling head fitted with means for rotating the cutting disc.

Figure 8 is a view in plan of a compensating element of a particular shape.

Figure 9 is a perspective view of a compensating element of a particular shape.

The drilling head (Fig. 1) comprises a rotating body 1 which screws on to the end of a shaft, not shown, driven in rotation. The upper part of the rotating body 1 has a part in the shape of a truncated cone 2 provided with a thread 3.

On the lower part of body 1 is a cylindrical section 4, the axis of which diverges downwards in relation to the axis of rotation of body 1. A disc 5 is rotatably mounted on the cylindrical section 4. The cutting surface of the disc has the shape of a truncated cone or, as shown in Fig. 1, it is composed of two opposed annular surfaces 6 and 7. The annular surface 7 is equipped with cutting devices. The cylindrical section 4 supports the disc 5 and is fitted with a ball-bearing 8 facilitating the rotation of disc 5. A shoulder 9 of the cylindrical section 4 serves as a thrust bearing for the disc and can also be fitted with a ball bearing 10. A nut 12 retains the disc 5 on its shaft 4, a seal 11 protecting the ball bearing 8 is placed between the nut 12 and the^^js—^. ball bearing 8. A roller 13 is provided on a shaft H'l _ 3 _ ^~30Cn$i5 which shaft lies parallel t.o the axis of rotation of 20151T the drilling head and is mounted between two horizontal plates 15 and 16 forming part of body 1. Generant 17 of the roller 13 and the furthest generant 7 of the 5 roller 13 from the axis of rotation of the device, are diametrically opposed. It is possible to equip the device with other rollers placed axially or at an angle to the axis of the device. A duct 18 runs through body 1 and has an outlet 19. The duct 18 serves to convey air, 10 water or mud to the bottom of the outlet 19 to lubricate and cool the disc and the water or mud serves to evacuate the drilled rock where a separate tubing or casing is provided for injection of the fluid. The section 4 on which disc 5 is mounted can also have a branch (not shown) 15 of duct 18 running through it and opening through an outlet (not shown) in nut 12. In this way, better cooling of the ball bearings 8 and 10 is obtained. The cutting surface of the disc can be fitted with ducts through which liquid is ejected under high pressure on to the surface 20 to be cut. Depending on the nature of the ground, this liquid penetrates the surface and facilitates cutting.

Drilling is carried out as follows: The body 1 is rotated in the conventional way and a slight load is exerted on the drilling head. The cutting surface of disc 5, being 25 equipped with teeth or being simply sharpened depending on the type of ground, shears the ground and creates a hole with a bottom 20 having an axial section with an approximately parabolic profile.

In the case of a disc fitted with teeth on the 30 cutting surface and locked in relation to its rotating y ^ ^11 " ' ' support 4 when the drilling head turns, the teeth cut o'til: r3;> 201517 a series of steps. Because of the load exerted on the drilling head, the disc 5 penetrates in relation to rotation and the horizontal side of the step created by one tooth is sheared by a following adjacent tooth describing a circumference bigger than that of the circumference described by the preceding tooth. If, however, the disc 5 is in free rotation around its support 4 and the vectorial sum of the forces exerted on its cutting surface not being nil, the resulting force rotates disc 5 around its support 4. In this way, each point of the wall is cut out under the effect of a force substantially perpendicular to the axis of rotation of the drilling head and at a tangent to the wall 20 and a force perpendicular to the rotating support 4 of the disc 5. These forces are due respectively to the rotation of the drilling head and to the free rotation of the disc 5.

Previously, and depending on the type of ground, a hole several centimetres deep must be drilled by other means so that a large part of the cutting surface of the cutting disc 5 is in contact with the ground. Without this precuation at the beginning of drilling, particularly on hard ground, the disc 5 tends to roll around its support 4, only a small part of its circumference being in contact with the ground. To ensure that the disc 5 rotates around its support 4 during drilling, the bottom tip 21 on the lowest cutting edge must be at least 1 mm offset from the geometric axis of rotation 23 of the drilling head. During drilling, the roller 13 rests against the side of the hole and counterbalances the reaction of the disc 5 against the wall and compacts the wall 201517 The version illustrated in Fig. 2 differs from the preceding version only in the shape of the roller and of the cutting surface of the disc. The roller 13' has the shape of a truncated paraboloid to coincide with the * profile of the wall 20 at the bottom of the hole. This same roller could replace roller 13 of the preceding version. For this version, the peripheral surface 7 of the disc 5 is in the shape of a ring cut in a spherical surface. The cutting surface in contact with the wall 20 has a maximum diameter which can be defined in this Figure by the length of the segment connecting points 21' and 22'. Point 22' and point 17' of the roller 13 can be at the same level, the position of the roller 13 relative to the disc 5 should be such that the drilling head remains in equilibrium during drilling, i.e. it does not oscillate around the drilling head. Point 17' is the highest point of the roller 13' in contact with the wall 20. It seems that the optimum diameter of the cutting surface 7' is that corresponding to the length of the side of an equilateral triangle inscribed in a circle having the same diameter as the drilled hole diameter. This length is represented on Figs. 1 and 2 by segments 21-22, and 21'-22' respectively.

For the rest of Fig. 2, the same references indicate the same elements previously described. The distance from point 21' to the centre of the hole is greatly exaggerated on the drawing. In reality it is a few millimetres and the point at the bottom of the hole is crushed by the cutting surface of the disc 5. Moreover, this point serves to keep the drilling head centered and in this case the roller or the counter-reacting element is not in continuous contact with 201517 the drilled wall. The cutting surface of the disc can be profiled so that as the ring-shaped cutting surfaces (with or without teeth) gradually wear, the adjacent surfaces take over the work while still continuing to 5 impart the same profile to the drilled hole. It is desirable for the axial profile of the hole to be approximately in the form of a double parabola, as shown in Fig. 2, because the middle point enables the drilling head to be automatically stabilized, the disc being in 10 a position slightly off centre of the hole axis.

The rounded shapes of both the roller and its support and of the cutting disc facilitate the withdrawal of the drilling head.

In cases where the walls of the hole must be 15 strengthened with tubes 27 (Fig. 3), the support 28 of disc 29 is part of an articulated arm 30 hinged around a shaft 31 perpencidular to the axis of rotation of the drilling head. Shaft 31 is mounted on a rotating cylindrical body 32 through which runs a duct 33 opening into the 20 shaft 31 which is hollow. On the side of shaft 31 are two holes 34 and 34' (Fig. 4) opening into duct 33 via a bent tube (not shown) forming an inverted U, the extremities of the U being connected to two holes 34 and 34' and the base of the U, which is equipped with a hole, 25 to duct 33. Two other holes on the side of shaft 31 connect duct 33 with a duct 35 running through support 28 of disc 29 and a second duct 36 of arm 30 when the drilling head is in working position as shown in Fig. 3. The articulated arm 30 has a cylindrical head through which shaft 31 passes. On part of its side surface the head has a cylindrical -is.

V ^ c ^7 •• tenon 39 having flat sides. The upper part of the head of arm 30 is lodged in a corresponding housing in the rotating body 32.

In the working position, one of the flat sides of the cylindrical tenon 39 contacts a corresponding surface of the rotating body, thus ensuring the angular positioning of cutting disc 29. A spring 37 is provided in a housing 38 between the head of the articulated arm and the rotating body. The spring 37 rests on one side against a surface 41 of the rotating body and, on the other side, against the second flat side 42 of the tenon 39 and biasses the shaft 30 back into a working position. A small tongue 43 being horizontal in the working position contacts the rotating body 32, also ensuring the angular positioning of disc 29 and, in addition, it contacts the lower end of wall support tubing 27 and draws support 2 8 of disc 29 into a vertical position, as shown in Fig. 5, when the drilling head is withdrawn from tubing 27. The end of the small tongue 43 slides against the inner wall of tubing 27, ensuring the correct positioning of disc 29 when it moves inside the tubing 27.

During drilling, a roller 24 mounted on a radially extensible arm 25 rolls either against the wall of the drilled hole or against the inner wall of tubing 27. Its main purpose is to act as a counter-balance to the reaction of the ground to disc 29 and to centre the drilling head. It also compacts and strengthens the wall of the hole if it rolls outside the tubing 27. When the drilling head is inserted or removed through tubing 27, the extensible arm 25 is in a retracted position to allow the device to pass through the tubing. Arm 25 can be a hydraulic jaqfe. 291517 Preferably, the roller should be at the same level as the upper part of the cutting surface of the disc or even lower to ensure the stability of the drilling head.

Fig. 6 shows schematically a variation on the design 5 allowing for the enlargement of the diameter of a hole 44 made by a drilling device corresponding to the drilling head described above or by another conventional means. For example, the hole, before its enlargement, may be drilled by a tricone.

The device shown has three cutting discs 45, 46, 47 placed at intervals and alternately on diametrically opposite sides of the rotating body. The diameter of the lowest disc 45 is smaller than that of the second disc 46 which, in turn, is smaller than that of the third disc 47.

The same applies to the length of their respective rotating supports 51 to 53.

In order to standardize construction, it is possible either to have cutting discs of the same diameter and rotating supports of different lengths, or vice versa.

The rotating body supporting the three rotating supports 51 to 53 of the cutting discs 45 to 47 can be made of a single piece but this design has the disadvantage of lack of flexibility in use, for example, in case of breakdown of one of the discs, the whole drilling head must be changed.

To avoid these disadvantages, each cutting disc 45 to 47 is mounted on its own rotating body 48 to 50. The lowest drilling head corresponds to the device in Fig. 1 and need not be described again. The body 4 9 which carries the disc 46 is attached on top of body 48 in such a way f-'J that the discs 45 and 46 are on diametrically oppositej_ _ 14 _ \\ - 201517 sides of the composite drilling head. To ensure the correct relative position of the two discs 45 and 46, the two bodies 48 and 49 are attached by a bayonet or other system. The third body 50 is mounted on the 5 second 49 in the same way, with the cutting disc 47 on the same side of the drilling head as the lowest disc 45.

Each of the rotating bodies has an axial duct 5 4 for the passage of cooling fluids or for evacuating 10 excavated rock where a separate tubing or casing is provided for injection of the. fluid. The axial ducts open into another and each has two branches, one running axially through the rotating support of the corresponding cutting disc (not shown), the other opening radially on 15 to the side of the drilled hole.

During enlargement of the hole 44, the first drilling element serves only as a guide and counter-balance to the second, and subsequent elements. The first drilling element can be a conventional drill-bit having served to 20 drill the pilot hole 44.

In this last variation of design, it is possible to do without the rollers corresponding to the upper discs, each disc serving to counter-balance the other.

In order to avoid radial distortions of the composite 25 rotating body, the axial distance between two cutting discs should be limited.

It seems that if the distance between the highest point of the first disc 45 and the lowest point of the following disc 46 is equal to the diameter of the previously 30 drilled hole, an acceptable distortion level is maintai^m^iv?^ /* A / v - 15 - k „ '4 | ^ soaring - - According to a variation of design not shown, it is possible to slightly displace the rotating support of the cutting disc in relation to the axis of rotation of the drilling head so that part of the cutting surface of the disc bears more heavily against the wall of the hole and increasing traction and tending to make the disc turn around its support. The angle defined by the displaced projected axis of rotation of the disc and by a straight line passing through the centre of the disc and the point of intersection of the virtual axes of rotation of the rotating body and the non-displaced disc should be between 1° and 5° to achieve the above-mentioned effect.

The drilling device described can be used for any sort of vertical, oblique or horizontal drilling in search of water, oil or mining exploration and exploitation. As a small amount of power is sufficient to operate the described device, it is very economic in use for underwater drilling where it is necessary to drill through layers of widely differing hardness, ranging from sand to the hardest rock. The same applies to horizontal drilling because a low axial power is sufficient for good operation. It can be used to good advantage in the building of tunnels. Since only the bearings used are for rotation of the discs, they can be ball, roller or needle bearings, mounted in such a way as to be water-tight, resulting in prolonged life.

A further embodiment envisages the use of plain bearings instead of roller bearings.

The cutting surface of the disc can be either a hard surface or equipped with teeth made from diamond, tungsten carbide or other substances, the choice being dictated by the type of ground to be drilled. / - 16 - / 7 ' \ 201517 The speed at which the disc rotates around its support, for the versions already described, depends on the speed of rotation of the shaft of the drilling head on which the disc support is mounted and on the vectorial resultant of the forces exerted on the surface of the disc. This dependence reduces the cutting action of the disc, prolongs working time and causes assymetrical wear of the cutting disc. The version in Fig. 7 enables these disadvantages to be remedied.

The drilling head comprises a rotating body 101 screwed to the end of the drill shaft 102, and carrying a motor unit 103. A cutting disc 105, illustrated diagrammatically, is mounted on an oblique support 104 housed in an oblique part 106 of the rotating body 101. A roller 108 is mounted 15 on the side diametrically opposite the oblique part 106 of the rotating body, its shaft 109 being borne by two parallel arms 110 and 111. The disc 105 is rotatably connected to the motor 103 through shafts 104 and 112 each fitted at one end with a bevel gear 113 and 114 20 respectively,meshing with a toothed idler wheel 115.

The shaft 112 drives the toothed wheel 115 transmitting motion to the shaft 104 turning the disc 105 which cuts into the wall 116 of the hole independently of the rotation of shaft 102. The motor unit 103 can be a 25 turbine driven by liquid circulating inside a duct, not shown, in the drill shaft 102 and rotating body 101 intended for the evacuation of debris. The speed of rotation of the disc 105 is independent of the speed of rotation of the drill shaft, therefore less pressure needs to be exerted on the cutting disc. In this 'iN arrangement, the cutting disc 105 works like a circular? ^ saw or a cutter, the main cutting effort of the disc 20151 being provided by the motor unit 103 and drive train. Depending on the type of ground, the cutting disc is fitted with teeth made of diamond, tungsten or other hard material.

Using the same principle, a machine can be produced for horizontal drilling, to extract coal for example. The essential difference is that tunnels drilled for raining exploitation have a far greater diameter- All that needs to be done in such cases is to mount on the existing spindle of a tunnel drilling machine a rotating body whose oblique part is much longer than the oblique part 106 of the body 101 of Fig. 7 as well as the arm or arms bearing the compensating roller or rollers. The oblique part of the rotating body being longer, a motor for driving the disc can be fitted directly on to this part of the rotating body. The operation of such a device is the same as that of the device in Fig. 7.

In order to follow the irregularities of the diameter of the hole better, due to the nature of the ground, the roller can be mounted on an extending arm.

A second solution is to use a roller whose section perpendicular to its rotational axis is elliptical (Fig.8). The roller represented in Fig. 8 is formed from an elliptical ring 120 in hard material such as tungsten surrounding a core 121 made of another material, for instance rubber. Through this core 121 is a cylindrical hole 122 for mounting the roller on a shaft 109. This roller is designed to slide against the wall and to roll only where there is an irregularity in the wall until the cutting disc 105 is in contact with the wall 116 of the hole. The roller^'r,-> to; 108 slides against the wall of the drilled hole with the part of its side surface of least radius. As soon as the roller is no longer in contact with the wall because of an irregularity (hole) in the wall, the drilling head is de-centred under the effect of the reaction of the disc 105 on the wall. The roller then comes into firm contact with the wall and starts rolling until the cutting disc 105 is brought into contact with the wall. The variation in drilled hole diameter must correspond at most to half the difference between the minor and the major axes of the ellipse in order to ensure efficient operation of the device. The roller returns to its original position as soon as the variation in the drilled hole diameter has been passed.

A third solution which has also been tested is to use an element with a friction surface mounted on an elastic support in place of the counter-reacting roller.

This solution makes it possible to avoid wear on the shaft of a roller with circular section which turns much faster than the drilling head. The friction surface can be the side surface of an approximately cylindrical or prism-shaped fixed element. When a part of the element surface in contact with the wall of the drilled hole has worn down, it can be turned so that an unworn part of the side surface faces the wall of the hole. Such an element-guide 130 is shown in Fig. 9. It consists of a prism, the edges and side surfaces being rounded. The side surfaces can be fitted with flexible teeth to absorb variations in diameter of the drilled hole. Element 130 is fixed and ^ set parallel to the drilling shaft so that one of its,/^ o When this face or edge is worn, element 130 can be ** turned and one of the other surfaces or edges brought forward. This non-rotating upper compensating guide is in effect a pre-set (to one of a number of positions) curved surface able to contact the side of the hole as cut by the lower disc. The compensating guide can be set to act only on the vertical wall of the hole or can be set at a lower level to impinge on the upper end of the curved base to the hole. The main object of the upper compensating guide is to ensure that particularly at the start of cutting a hole the lower disc is seated at a position causing a cut eccentric from the centre line of the hole.

N-- 201517

Claims (23)

WHAT WE CLAIM IS:

1. A drilling device for drilling holes in the ground comprising a drilling head including a rotating body through which runs a duct for supplying, under pressure, air, or mud, or water or other drilling fluid and carrying 5 at least one rotating cutting element mounted on a support fixed on the rotating body so that the axes of rotation of the rotating body and of the cutting element diverge in the drilling direction and, wherein the cutting element is a disc having at least one annular cutting part and 10 wherein the rotating body carries on the opposite side to that carrying the rotating support of the disc at least one counter-reacting eleme/it placed in such a way that the said element contacts a wall of the hole being drilled to centre the drilling head by compensating for 15 the radial component of the reaction of the wall to the disc and to compact and strengthen the wall.

2. A device according to claim 1, wherein the counter reacting element is a roller mounted on a shaft whose axis lies parallel to the drilling direction. 20

3. A device according to claim 2, wherein the roller outer surface profile is in the shape of a truncated paraboloid to correspond with the wall surface at the base of the drilling.

4. A device according to claim 2 or 3, wherein the 25 roller has an elliptical section when viewed along its rotational axis.

Z015V*;5. A device according to any one of the claims 2;to 4, in which the highest points of the annular cutting part of the disc and of the roller when the device is in an upstanding or vertical position, are at such heights as 5 to ensure that the drilling head is in equilibrium during drilling.;

6. A device according to claim 1, wherein the counter-reacting element has a friction surface.;

7. A drilling device according to any one of the claims 10 1 to 6, wherein the drilling head includes means for rotating the cutting disc around its support independently of rotation of the rotating body.;

8. A device according to claim 7, wherein the means for driving the cutting disc consist of a motor integral;15 with a drill shaft carrying the drilling head and a device drivingly connecting the motor and the cutting disc.;

9. A device according to claim 8, wherein the motor is a turbine driven by a fluid circulating in the duct of the drilling device.;20

10. A device according to claim 7, wherein the driving means are integral with the rotating support of the disc.

11. A device according to any one of the claims 1 to 10,;wherein the counter-reacting element is supported by an extensible radial arm such as a jack or a piston. 25

12. A device according to any one of the claims 1 to 11,;wherein the greatest diameter of the annular cutting part is approximately equal to the length of a side of an equilateral triangle inscribed in a circle of the same diameter as the drilled hole. •••• \;/\ " ~ A;/ • (;.. i, i Cu;

13. A device according to any one of the claims 1;201517;to 12, wherein the rotating support of the disc is carried by an arm hinged around an axis perpendicular to the axis of rotation of the rotating body so that the rotating support of the disc can be either at an angle to the rotating axis of the rotating body or form an extension or an offset extension to the said axis.;

14. A device according to claim 13, wherein the hinged arm is fitted with resilient means biassing the rotating support of the disc at an angle to the rotating axis of the rotating body.;

15. A device according to claim 1, wherein, the drilling head comprises at least two cutting discs whose rotating supports are mounted on the said rotating body at regularly spaced positions along its length and placed alternately on diametrically opposed sides.;

16. A device according to claim 15, wherein the drilling head is made up of at least two rotating bodies each bearing a cutting disc and attached to each other end to end by components that assure the relative positions of the rotating supports of the respective cutting discs.;

17. A device according to claim 15 or 16, wherein the diameter of the cutting discs and/or the length of their respective rotating supports increase progressively, the smaller or smallest dimensions corresponding to the lower or lowest cutting disc.;23;201517;

18. A device according to any one of the claims;1 to 17, wherein the rotating body is equipped with a pilot drill-bit at its lower end.;

19. A device according to any one of the claims;5 1 to 17, wherein the lower point of the cutting surface of the disc situated at the lower end of the rotating body is at a radial distance of at least 1 mm from the projected rotating axis of the said rotating body.;

20. A device according to any one of the claims 1 to 10 16, wherein the rotating support of the cutting disc has a duct running through it for supplying, under pressure, air or water or mud or any other drilling fluid emerging either near the centre of the disc or from ducts provided on the cutting surface of the disc 15 for ejecting fluid under pressure against the wall of the hole.;

21. A device according to any one of the claims 1 to 20, wherein the geometrical axis of the rotating support of the cutting disc and the geometrical axis of;20 rotation of the rotating body do not pass through a common point.;

22. A device according to claim 21, wherein the angle formed by the projected displaced rotating axis of the rotating support of the disc and the straight line;25 joining the centre of the disc to the point where the projected rotating axes of the rotating body and the disc would intersect if the latter were not displaced,;is between 1° and 5°.;- 24 -;b^ f';V V . V;2015:1*7

23. A drilling device substantially as described herein with reference to any one of the embodiments shown in Figures 1 to 9 of the accompanying drawings. - 25 -