GB2183777A - Mole assembly - Google Patents

Abstract

A mole assembly has a rigid elongate member 9 between a mole 3 and a draw line 5' for the mole 3. The elongate member 9 may be connected to the nose 11 of the mole by a coupling member 10, preferably flexible. This permits at least a part of any radial component of the tractive force from the draw line 5' on the mole to be decoupled onto the rigid member 9. The rigid member 9 spreads its radial loading as it contacts the wall of the duct 1, and so does not break out of the duct 1, even when the duct 1 is not straight. Thus the mole 3 is constrained to follow approximately the centre line of the duct 1. The coupling member 10 may be replaced by a direct articulation between the elongate member 9 and the nose 11 of the mole 3. <IMAGE>

Description

SPECIFICATION Mole assembly This invention relates to a mole assembly. A mole is a tool which is caused to move through earth in order to form a duct through that earth, or to clear or enlarge an alreadyexisting duct.

Moles are powered tools, normally pneumatically powered, for breaking a path through the ground. They have a head which is caused repeatedly to impact against the surface directly in front of the mole. To achieve this the head is attached to an anvil against which strikes a piston. The piston reciprocates due to pneumatic pressure from e.g. a compressed air supply to the mole. The pressure causes the piston to move forward, until it strikes the anvil, at which position (or slightly in advance of which position) the movement of the piston opens a valve, releasing the air behind it, which may then act as a return force on the piston. The head of such a mole has a nose extending from it, to which is normally secured a draw line to pull the mole through e.g. the ground with the impacts of the mole head opening up a passage for the mole.

The present assembly is for use when a mole is in operation to clear or enlarge an existing duct and in particular in the case where a mole is being used to destroy an existing lining of a duct so that that lining may be replaced by a new and more efficient one, with or without enlargement of the size of the duct.

The mole has to follow the centre line of the existing duct. It is not permissible for it to "cut corners". But the existing duct may have been laid crooked or may have become crooked through subsidence etc. in the surrounding soil and in such a case when the mole is being drawn towards an access point by a line run through the duct, a deviation in the duct ahead of the mole may cause the tractive force of the line to be applied in such a way as to cause the mole to tend to cut the corner, i.e. to break out of the side wall of the duct and follow a more or less direct path towards the source of the pull on the line. This is very undesirable, especially because of the possible presence of other underground services in the track of the mole.

We have found a way of avoiding this problem which is effective in the vast majority of cases (it could not deal with gross deviations in a straight line or sharp angled bends).

The present invention proposes that an elongate rigid member is attached between the draw line and the nose of the mole, with a flexible link between the elongate member and the mole. This flexible link may be achieved by connecting the member to the mole by a chain, cable or other similar flexible elongate link, but preferably a simple articulation is provided between the mole and the elongate member. It would also be possible to provide a rigid link articulated to both the nose of the mole and the elongate member, thereby to provide flexibility between the elongate member and the mole, but this has few practical advantages over a single articulation, and is more complex.

The effect of this is to decouple at least a substantial portion of the radial component of the tractive force due to the deviation in the duct from the mole itself and to spread the decoupled part onto at least the leading part of the articulated member. This will spread its radial loading as it contacts the wall of the duct and maintain itself in progression along the unbroken duct liner without breaking out of the side of the duct. Its trailing end draws the mole after it and tends to preserve it along the centre line of the duct.

The length of the elongate member is determined primarily by the length of each pipe section, since the bends are caused by differences in orientation between one section and the next. The member should ideally be of comparable length with a pipe section but in practice lengths of 21 to 4 of the pipe section are satisfactory. The thickness of the member is also primarily determined by the diameter of the pipe section, but in practice the thinkness is not critical.

The invention is illustrated by the schematic drawings wherein; Figure 1 is a section through a duct with a mole being pulled through it in accordance with the prior art; and Figure 2 is an equivalent section of an embodiment of the invention.

In Fig. 1 an existing duct is lined with a lining 1 which is to be broken as at 2 by the passage through the duct of a mole 3 which is of a diameter larger than that of the duct.

The mole may draw behind it a new lining 4.

The mole is pulled through by a draw line 5 drawn by a winch or the like at an access point gained by excavation.

Te duct illustrated in Fig. 1 has a deviation in it and the line 5 is bent at the position 6 and has a tendency to break through the lining 1 of the duct. The line is under very considerable tension-the loads may be as high as 10 tons, so even on a small deviation there is a very substantial radial force (perpendicular to the direction of the line). If the line breaks through the duct lining 1 there will be a strong tendency for the mole to follow also the direction of the line, break right through that lining and start a new bore through the earth pointing directly at the winch.

A possible such track is indicated by dotted lines 7.

According to the invention as seen in Fig. 2 a connecting unit 8 is interposed between the draw line 5' and the mole 3. This unit 8 includes an elongate rigid member 9 and a cou pling member 10. The rigid member 9 is a cylinder (it may be a hollow cylinder), and its diameter is greater than that of the line (normally much greater) but is less than that of the mole, for example approximately half the diameter of the mole. The coupling member 10 is preferably flexible e.g. is a chain or cable, and links the trailing end of the rigid member 9 to the nose 11 of the mole 3 linkages 12, 13 allowing limited axial deviation between the members 9, 10, 11 respectively.

As seen in Fig. 2, since the member 9 is rigid and is of substantial axial length (for example being between 1 metre and 2 metres long, somewhat less than the length of the pipe) it has the effect of cutting down on the effective deviation in the duct from the point of view of a direct line to the winch and, when there is a deviation, of spreading any radial (perpendicular) load against the inner wall of the linking 1 by virtue of its substantial diameter e.g. 25 to 50 mm less than that of the lining. Furthermore as its leading end is pulled past the end of a deviation there will be a tendency for its rear end to pivot on the fulcrum formed by the edge of the deviation thereby bringing the junction 12 back towards the centre line of the duct, and accurately pulling the mole along that centre line.

The length of the coupling member 10 is regulated by the expected deviation in the linings. At least if it is effectively flexible (e.g.

being a length of chain). If it is too long the avoidance of "corner cutting" will start to be lost; then its length may suitably be between one quarter and equal to the length of the member 9.

In another embodiment of the invention, however, the coupling member 10 may be omitted, so that there is an articulated connection of the linkages 12, 13. Although this limits the amount of pipe deviation that can be accommodated, it has been found satisfactory for most practical situations where the pipe was originally laid straight, and has become crooked through subsidence.

Claims (8)

1. A mole assembly comprising a mole adapted to be drawn by a draw line, and an elongate rigid member of thickness less than the diameter of the mole connected between the draw line and the mole, there being a flexible link between the member and the mole.

2. A mole assembly according to claim 1, wherein the flexible link is an articulation.

3. A mole assembly according to claim 1, wherein the link is a flexible elongate member.

4. A mole assembly according to any one of claims 1 to 3 wherein the mole terminates in a nose to which the flexible link is connected.

5. A mole assembly substantially as herein described with reference to and as illustrated in Fig. 2 of the accompanying drawings.

6. A method of clearing or enlarging a duct comprising drawing a mole assembly according to any one of the preceding claims through that duct, wherein the diameter of the mole is greater than the minimum diameter of the duct, and the thickness of the elongate member is less than the minimum diameter of the duct.

7. A method of clearing or enlarging a duct according to claim 6, wherein the duct is defined by a plurality of pipe sections, and the length of the elongate member is at least half that of each pipe section.

8. A method of clearing or enlarging a duct substantially as any one herein described with reference to and as illustrated in Fig. 2 of the accompanying drawings.