GB2259103A

GB2259103A - Improved drilling apparatus

Info

Publication number: GB2259103A
Application number: GB9218156A
Authority: GB
Inventors: Malcolm Clark; Alan D Brodie
Original assignee: Compair Holman Ltd
Current assignee: Compair Holman Ltd
Priority date: 1991-08-30
Filing date: 1992-08-26
Publication date: 1993-03-03
Also published as: GB9218156D0

Abstract

A tool for enlarging a previously formed hole, comprises a body 14 shaped to pass through the hole and to enlarge it by compressing the surrounding material as it passes, and at least one cutter (18) in association therewith for cutting a channel parallel to the hole as the tool body 14 is passed along it. The tool is used for simultaneously laying a cable 11 and installing a protective/warning strip 24 above the cable 11. <IMAGE>

Description

IMPROVED DRILLING APPARATUS The present invention relates generally to drilling apparatus and to an improved hole-enlarging tool for use with such drilling apparatus.

The present invention also comprehends drilling apparatus incorporating a tool having means for forming an additional slot or channel parallel to the hole formed by the drilling apparatus as it is being enlarged. Such a slot may be used, for example, when the drilling apparatus is used for cable laying. Public utilities such as electricity, water, gas and telecommunications are usually supplied via an underground network of cables, pipes and ducts. Installing or replacing sections of these conduits can be relatively easy in areas where there is no surface development and may be achieved by simply excavating a trench along the desired cable or pipe path. However, in built-up areas trench digging is neither easy nor desirable and opening sections of road surface is expensive and often inconvenient.

It is known that the need to dig a trench can be circumvented by using directional drilling apparatus.

The use of such apparatus involves digging an access pit at the chosen start point and introducing a drill bit and rod. Alternatively a so-called "surface launch" technique may be used in which the drill bit and rod are driven at a shallow angle into the ground from the surface. The drill bit head is provided with means, which enables the user to monitor and control the orientation and depth of the drill head. For example the leading drill rod may have a drill bit or head hving an inclined face and the drill rods of the drill string may be rotated continuously whilst being advanced.

Directional control can be achieved by temporarily stopping the rotation whilst advancing the rods thereby allowing the inclined surface to cause lateral deflection of the drill head. Detection apparatus on the surface is used to determine the location of the drill head as drilling proceeds.

Thus, as the drilling operation progresses, the operator can follow the path of the drill head underground until a desired exit point is reached. At this point, the drill bit may be replaced by a tool head or reamer to which the new cable or pipe is attached. The reamer is then retracted back through the bore hole by, for example, hydraulic means thereby pulling the cable or pipe into place.

Such methods have been successfully used for laying a variety of pipes and cables, but have been less suitable for installing electricity cables. In order to dissipate heat efficiently from such cables, it is desirable to install them directly into soil, without any surrounding ducting. However, under health and safety legislation, underground electricity cables must have a protective marking strip situated above the cable, which is strong enough to prevent accidental contact with the cable.

Since previously proposed directional drilling systems had no facility for laying such a protective strip, the equipment was not suitable for laying electricity cables.

According to one aspect of the present invention a tool for enlarging a previously formed hole comprises a body shaped to pass through the hole and to enlarge it by compressing the surrounding material as it passes, having at least one cutter in association therewith for cutting a channel parallel to the hole as the tool body is passed along it.

The cutter in association with the tool body may have various different forms, and may be a single cutter or a set of cutter elements. The means by which the cutter is associated with the tool body may also vary. In a first embodiment of the invention the cutter is spaced from the tool body and joined thereto by a pylon. Conveniently such a cutter has a cutting edge extending transversely of the longitudinal axis of the cutter body.

The cutter may be positioned, in relation to the tool body rearwardly thereof (in the direction of intended motion when drawn through the hole) such that in use the cutting edge of the cutter contacts material previously compressed by the passage of the body.

Alternatively, however, the cutter (or an additional cutter) is held in position in advance of the reamer body in relation to the direction of intended movement. The cutter may have an associated slot-enlarger body associated therewith so as to be drawn with the holeenlarging tool as this is drawn through the hole.

The position and/or orientation of the cutter may be adjustable in relation to the body.

In order to balance the forces exerted on the body of the hole-enlarging tool as it is drawn through the hole the body may be provided with one or more additional projections extending transversely of the axis of the tool body and so dimensioned as to offer a resistance to passage of the same order of magnitude as that offered by the cutter and/or the means by which the cutter is linked to the tool body. Such projections may have associated secondary cutters operable to provide additional channels parallel to the longitudinal hole through which the tool body is drawn, for purposes which will be described in more detail herein below.

The tool of the present invention may further be provided with means for attaching to it or to the cutter a leading edge of the strip of material to be drawn into the slot cut by the cutter as the body is drawn through the hole.

In order to compensate for variations in the material through which the body is drawn, especially as such variations may cause the cutter to become displaced from its intended position of orientation in relation to the hole through which the body is being drawn, whereby for example to follow a helical or partly helical path, the tool of the present invention may further include means for altering the geometry of the tool body, and/or the cutter, and/or the attachment means linking the cutter to the tool body whereby to effect a degree of "steering" of the cutter during use as the tool body is drawn through the elongate hole.

According to one aspect of the present invention, there is provided a method of installing an elongate element underground with a protective strip in parallel spaced relationship thereto, comprising the steps of driving the drilling means underground between a start point and an end point to form a bore hole, exchanging a drilling means for a tool as hereinabove defined at the said end point, attaching one end of a protective strip to the said tool, and pulling the tool back through the bore hole thereby drawing the elongate element and the protective strip together in a parallel spaced relationship.

According to a second aspect of the invention, there is provided apparatus for drilling a bore hole and installing underground elongate elements therein, comprising drilling means having a drill head element cable of being driven through the ground and actuating means for effecting movement of the drilling means, in which the drilling head element is interchangeable with a tool as hereinbefore defined.

Various embodiments of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a preferred embodiment of the tool of the invention; Figure 2 is a front elevation of the tool shown in Figure 1; Figure 3 is a side elevation of the tool shown in Figure 1.

Figure 4 is a schematic side view of a further embodiment of the invention, provided with a cutter in the form of a flat "wing" mounted on the tool body by a pylon; Figure 5 is a schematic perspective view of the embodiment illustratedin Figure 4; Figure 6 is a schematic perspective view of a third embodiment of the invention; and Figure 7 is a schematic side view of a further embodiment of the invention; and Figure 8 is an axial sectional view of a further embodiment of the invention.

Referring to the drawings, there is shown a reaming means 14 capable of cooperating at one end 12 thereof with the pipe or cable 11 to be installed. To its upper surface is attached by means of a connector 10 a substantially planar wing means 16 with a substantially sharp forward cutting edge 18 and a rearward attachment surface 20 adapted to be connected to a protective strip 24.

Attachment can be effected in a number of ways, but in the illustrated embodiment a plate 22 is fixed onto the rearward attachment surface 20 thereby clamping the end of the marker strip 24. The relative dispositions of the reaming means 14 and the wing means 16 are shown in Figure 3. In the preferred embodiment they are about 15 cm apart but the spacing may be altered. Figure 2 shows the substantially T-shaped cross section of the reaming means and wing means.

In use of the device, directional drilling equipment is used to drill a bore hole from an access pit to an exit pit along a predetermined route. At the exit pit the drilling head element is removed and replaced by the reaming means of the invention. The cable to be laid is attached to the reaming means and its protective strip is attached to the wing means 16. As the reamer and wing unit is pulled back along the bore hole, the cable is drawn through the hole behind the reaming means and the sharp forward cutting edge 18 of the wing means 16 cuts a path through the soil parallel to and above the bore hole. Thus, the protective strip 24 attached to the trailing edge of the wing is installed in- the soil parallel to and spaced above the cable with an insulating layer of soil in between. Using such equipment, both the cable and its protective strip may be laid simultaneously.

Referring now to Figures 4 and 5 the tool shown comprises a body generally indicated 30 having a substantially cylindrical form with a tapered forward portion 31 and a connector 32 by which the body may be secured, for example by means of a screw threaded coupling, to a drill rod preliminarily past through the ground by a drill pushing or driving machine (not illustrated) which may be of otherwise known type. In order to connect the holeenlarging tool to a drill rod the connector portion 32 is formed with an internally threaded socket 13 for receiving a threaded spigot at the end of the drill rod.

At its rearward end the body 30 has a coupling 34 for connecting a cable or other linear element which is to be drawn through the enlarged hole. Projecting from the body 30 is a pylon 35 extending, as viewed in Figures 4 and 5, upwardly and rearwardly from the body 30 and transversely of the pylon extends a cutter 26 in the form of a "wing" having a relatively sharp leading edge 17 and means 28 at the trailing edge for connecting to a strip of material to be drawn through the slot which is cut by the cutter 26 as the body 30 is drawn through the hole.

As will be appreciated from Figures 4 and 5, the inclination rearwardly of the pylon 15 locates the cutter 26 with its leading edge 17 entirely behind the body 30 (in the direction of intended movement, namely from right to left in Figure 4) so that the cutter 26 in use acts on material previously compressed by the passage of the body 30 thereby ensuring that, as the tool is drawn through the hole, any tendency for the slot formed by the cutter 26 as it passes through the material to close is minimised.

Figure 6 illustrates an alternative embodiment in which the resistance to motion exerted by the pylon 15 and cutter 26 is, at least partly, compensated by the provision of two inclined fins 19, 40 located at 1200 with respect to the pylon 15. The fins 19, 40 are shorter than the pylon 15 and serve to equalise the forces on the body 30 which may tend to divert it from its passage through the opening previously formed by the drill rod thereby minimising any out-of-balance forces on the coupling 13 which may cause this to distort and result in difficulty in subsequent release.

Figure 7 illustrates a further alternative embodiment in which the reference numerals used in embodiments of Figures 4 to 6 are used to identify the same or corresponding components. In this embodiment a forward pylon 21 is provided near the forward end of the body 30 to carry the cutter 26 at a point close to the coupling 32. The pylon 15 in this embodiment carries a slotenlarging body 42 similar to the cutter 26, but having a greater thickness, which in use will follow the slot preliminarily cut by the cutter 26, and enlarge this in order to allow the strip 23 secured to the slot-enlarging body 42, to be drawn along with the minimum frictional resistance.

The embodiment of Figure 8 is similar to that of Figures 4 and 5, but is provided with an adjustable pylon 15 which, as can be seen from Figure 8, is pivotally mounted to turn about an axis transverse the longitudinal axis of the body 30. Rotation of the pylon 15 about the pivot axis 44 is achieved by a cable 25 pivotally connected at 46 to a lever arm 27 within the body 30. The cable 25 passes out through the coupling 32 and longitudinally through the centre of the drill rods (not shown) to the control apparatus at the launching end of the rods. By exerting a tension on the cable 25 greater or less than that exerted on the drill rods the lever arm 27 may be caused to turn about the pivot 44 in one direction or the other whereby to cause the angle of attack of the cutter 26 to increase or decrease. This arrangement may be of convenience for effecting a degree of "steering" of the tool as it is drawn through the ground: similar steering arrangements for the fins 19, 40 of the embodiment of Figure 6, and/or for turning the pylon 15 about an axis perpendicular to the axis of the pivot 44, may also be provided.

Claims

1. A tool for enlarging a previously formed hole, comprising a body shaped to pass through the hole and to enlarge it by compressing the surrounding material as it passes, having at least one cutter in association therewith for cutting a channel parallel to the hole as the tool body is passed along it.

2. A tool as claimed in Claim 1, in which the said cutter means comprises a single cutter element.

3. A tool as claimed in Claim 1 or Claim 2, in which the cutter is spaced from the tool body and joined thereto by a pylon.

4. A tool as claimed in any preceding Claim, in which the said cutter has a cutting edge extending transversely of the longitudinal axis of the cutter body.

5. A tool as claimed in any preceding Claim, in which the cutter is positioned, in relation to the tool body, rearwardly thereof (in the direction of intended motion when drawn through a hole) such that in use the cutting edge of the cutter contacts material previously compressed by the passage of the body.

6. A tool as claimed in any preceding Claim, in which the or a cutter is held in position in advance of the reamer body in relation to the direction of intended movement.

7. A tool as claimed in any preceding Claim, in which the or each cutter has an associated slot-enlarger body associated therewith so as to be drawn with the holeenlarging tool as this is drawn through the hole.

8. A tool as claimed in any preceding Claim, in which the or each cutter is adjustable in relation to the body.

9. A tool as claimed in any preceding Claim, in which the body is provided with one or more additional projections extending transversely of the axis of the tool body and so dimensioned as to offer a resistance to passage of the same order of magnitude as that offered by the cutter and/or the means by which the cutter is linked to the tool body.

10. A tool as claimed in. Claim 9, in which the said projections have associated secondary cutters operable to provide additional channels parallel to the longitudinal hole through which the tool body is drawn.

11. A tool as claimed in any preceding Claim, further provided with means for attaching to it, or to the cutter, a leading edge of a strip of material to be drawn into the slot cut by the cutter as the body is drawn through the hole.

12. A tool as claimed in any preceding Claim, further including means for altering the geometry of the tool body and/or the cutter and/or the attachment means linking the cutter to the tool body whereby to effect a degree of steering of the cutter during use as the tool body is drawn through the elongate hole.

13. A tool for enlarging a previously formed hole, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

14. A method of installing an elongate element underground with a protective strip in parallel spaced relationship thereto, comprising the steps of driving the drilling means underground between a start point and an end point to form a bore hole, exchanging a drilling means for a tool as claimed in any preceding Claim at the said end point, attaching one end of a protective strip to the said tool, and pulling the tool back through the bore hole thereby drawing the elongate element and the protective strip together in a parallel spaced relationship.

15. Apparatus for drilling a bore hole and installing underground elongate elements therein, comprising drilling means having a drill head element capable of being driven through the ground and actuating means for effecting movement of the drilling means, in which the drilling head element is interchangeable with a tool as claimed in any of Claims 1 to 13.

16. A method of installing an underground elongate element substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.

17. Apparatus for drilling a bore hole and installing an underground elongate element, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.