GB2164411A

GB2164411A - Pipe mole

Info

Publication number: GB2164411A
Application number: GB08421522A
Authority: GB
Inventors: Brian Arthur Robbins
Original assignee: Water Research Centre
Current assignee: Water Research Centre
Priority date: 1984-08-24
Filing date: 1984-08-24
Publication date: 1986-03-19
Also published as: GB8421522D0; GB2164411B

Abstract

Apparatus for use in underground pipe replacement comprises an outer casing having a probe (1) which is adapted to fit into an existing pipeline, a frusto-conical portion (6) leading from the probe (1) and having a smaller end having substantially the same diameter as the outer diameter of the probe and a larger end having a diameter which is greater than that of the existing pipeline, and a cylindrical portion (11) leading from the larger end of the frusto-conical portion and having substantially the same diameter as said larger end. A driving unit including an impact mole (20) is located within the outer casing and is spaced from the cylindrical portion (11). The space between the mole (20) and the cylindrical portion (11) is adapted to receive the leading end of a replacement pipe (30). Means are provided for forcing the pipe through a bore created by the outer casing by acting on the trailing or rearward end of the replacement pipe. Further means are provided for withdrawing the driving unit from the outer casing through the replacement pipe (30) by means of a cable attached to the rear end of the driving unit, whereby the latter can be withdrawn from the outer casing while leaving said casing in situ to allow repair of the unit or temporary use of the original and replacement pipe combination. <IMAGE>

Description

SPECIFICATION Improvements in pipe replacement This invention relates to apparatus for use in the replacement of pipes underground.

It is known, for example, from British Patent Specification No. 2113795 to replace existing underground pipework by driving an expander into an existing pipeline with sufficient force to deform the pipe outwardly so that it is compressed into the surrounding ground and by feeding a new pipe into the space formerly occupied by the existing pipeline.

The expander should be driven with sufficient force to ensure that the existing pipe can be deformed radially outwardly and compressed into the surrounding material which may be concrete or soil.

A known apparatus for performing the above-described method of pipe replacement comprises a conical or frusto-conical member adapted to engage the end of an existing pipe with its smaller end having a smaller diameter than the internal diameter of the pipe and its larger end having a diameter which is at least as great as the external diameter of the pipe, a jacket secured to the larger end of the conical or frusto-conical member and means for driving the said member into the pipe to cause the latter to be forced radially outwards and compressed into the surrounding ground by the forward movement of the conical or frusto-conical member and jacket. The drive means took the form of a pneumatic percussive device referred to in the art as an impact mole.

Pipelines are often replaced or fresh pipelines are often laid with the use of impact moles at locations at which the excavation of a trench is either impossible, for example under buildings, or would cause great inconvenience and disruption of vehicular traffic, for example under railway lines or roadways.

A problem encountered with the existing apparatus is that if the mole breaks down while in operation it cannot readily be recovered. The mole thus constitutes a blockage in the ~pipe which renders the pipeline unusable. In order to recover the mole, it is then necessary to carry out costly excavation of a trench in the region of the pipeline at which the mole is located. However, this may not be possible if the location is inaccessible, for example under a building, in which case the mole must be abandoned and a new pipeline must be laid. Quite apart from the loss of costly equipment, which must be written off, there is also the question of considerable delay in laying a new pipeline which can cause great inconvenience.On the other hand, even if the location at which the mole has broken down is accessible, this can often be in the middle of a railway line or roadway and the excavation of a trench at such a location would cause severe disruption to the railway timetable or to traffic flow which it had originally been intended to avoid by the use of a mole.

The present invention seeks to overcome this problem by providing means for retracting a mole from a pipeline.

According to the invention, there is provided apparatus for use in underground pipe replacement, which apparatus comprises an outer casing having a probe which is adapted to fit into an existing pipeline, a frusto-conical portion leading from one end of the probe and having a smaller end having substantially the same diameter as the outer diameter of the probe and a larger end having a diameter which is greater than that of the existing pipeline, and a cylindrical portion leading from the larger end of the frusto-conical portion and having substantially the same diameter as said larger end; a driving unit including an impact mole located within said outer casing and spaced from the cylindrical portion thereof, the space between the driving unit and the cylindrical portion of the casing being adapted to receive the leading end of a replacement pipe, means for forcing the pipe through a bore created by the outer casing, said means acting on the trailing or rearward end of the pipe; and means for withdrawing the driving unit from the casing through the replacement pipe, said withdrawing means comprising a cable or like means attached to the rear end of the driving unit, passing through the replacement pipe and attached to drive means beyond the trailing or rearward end of the said replacement pipe whereby the driving unit can be withdrawn from the outer casing while leaving said casing in situ.

By means of the apparatus according to the invention, the driving unit may readily be recovered, and if necessary replaced, in the event of a breakdown.

There is desirably no direct mechanical connection between the replacement pipe and the casing or the driving unit so that the pipe can be progressively advanced through a bore created by the driving unit and casing without said pipe being subjected to impact forces generated by the driving unit.

Preferably, sealing means are provided between the cylindrical portion of the casing and the leading end of the replacement pipe and between the driving unit and the said leading end of the replacement pipe. The sealing means may take the form of annular seals, such as O-rings, located in grooves respectively in the casing and the driving unit. Alternatively, the annular seals may be clamped to the casing and to the driving unit.

The driving unit desirably comprises an impact mole having a probe and a frusto-conical nose member mounted on its front end and a partially-tapered cylindrical spigot mounted on its rear end, said spigot having means for at taching thereto a cable or like means.

According to a preferred embodiment of the invention, automatic control means are provided for co-ordinating the rate at which the replacement pipe is advanced with the drive of the driving unit, said means permitting relative rotational and axial movement between the casing and driving unit on the one hand and the replacement pipe on the other hand while preventing separation of these components. The automatic control means desirably comprise at least one micro-switch arranged to control the operation of a valve located in a pneumatic line leading to the mole.

The invention will now be further described, by way of example, with reference to the drawings, in which: Figure 1 is a vertical section of one embodiment of an apparatus according to the invention; and Figure 2 shows, diagrammatically, the apparatus illustrated in Fig. 1 equipped with an automatic control arrangement.

In the drawings, like parts are denoted by like reference numerals.

Reference will first be made to Fig. 1 of the drawings in which the apparatus according to the invention comprises an outer casing which consists of a probe 1, a frusto-conical portion 6 and a cylindrical portion 11. The probe 1 consists of a tubular member to one end of which is secured, e.g. by welding, a tapered nose cone 2. A series of ribs 3 are secured to the body of the probe 1 on its outer surface. The ribs are desirably secured to the probe body by welding and six ribs are preferably provided equi-spaced around the external periphery of the probe body.

The smaller end of the frusto-conical portion 6 is adapted to fit over a rearward portion 4 of the probe 1, which portion is of reduced diameter to form a step on the probe 1 against which the smaller end of the frustoconical portion is arranged to abut. The said reduced diameter portion 4 of the probe 1 may be provided with an external screwthread arranged to co-operate with a corresponding internal screw-thread provided on the frusto-conical portion 6. A series of balls 5 of nylon or like material are located in a recess in the screw-thread in the reduced diameter portion 4 and compressed by the frusto-conical portion 6 as it is screwed onto the reduced diameter portion 4 to prevent the portions 4 and 6 from unscrewing under impact stresses imposed when the apparatus is in use.

The frusto-conical portion 6 of the outer casing is likewise provided on its outer surface with a series of ribs 7 and its larger end is provided with a cylindrical spigot 8 which is adapted to receive one end of the cylindrical portion 11. This portion comprises an outer shroud which is provided with an inner sleeve 12 which is arranged to fit over the spigot 8 and to be secured thereto by a series of screws 13 which pass through aligned bores in the outer shroud 11 and sleeve 12 and engage in respective screw-threaded bores in the spigot 8. An annular seal 14, in the form of an O-ring or the like is fitted on the spigot to provide a seal between the frusto-conical portion and the cylindrical portion of the casing. The outer surface of the shroud 11 may also be provided with a series of ribs (not shown) which may also be secured to the shroud by welding.

The interior of the frusto-conical portion 6 is provided with a raised region defining a tapered abutment surface 9 and a cylindrical bore 10. A locating probe 21 of a driving unit is adapted to be received in said bore 10, the driving unit having a tapered impact surface 22 which is designed to abut against the abutment surface 9. The driving unit further comprises an impact mole 20 which is of conventional construction so that a description of the internal components will not be necessary to a person skilled in the art.

The impact surface 22 is provided on a cylindrical nose member 23 which is adapted to fit onto the front end of the casing of the mole 20. The nose member 23 is held in place by engagement with the mole casing and with a clamp ring 24. The locating probe 21 is mounted on the front end of the mole 20 and is secured thereto by coupling pins 27. The locating probe 21 is further provided with an external screw-thread which is arranged to co-operate with a corresponding internal screw-thread on the clamp ring 24 by means of which the clamp ring can be screwed onto the probe 21 until the clamp ring engages in a step provided in the nose member 23 to hold said nose member in position on the mole. An annular sealing ring 25 of rubber or like material is located on the locating probe 21 and is held in place by a further clamp ring 26 which is likewise screwed onto the locating probe. The sealing ring 25 is arranged to be located in the bore 10 to provide a seal between the driving unit and the interior of the sleeve 12 in order to prevent the ingress of dirt and moisture into the space between the driving unit and the sleeve.

A partially-tapered, cylindrical spigot 28 is secured to the rear end of the mole 20, the diameter of said spigot being considerably less than the internal diameter of the sleeve 12 so that the leading end of a replacement pipe 30 can be accommodated in the annular space between the sleeve and the driving unit.

Again, in order to prevent the ingress of dirt and moisture into the said annular space, which could interfere with the operation of the apparatus, seals are provided. The seal on the casing comprises an annular multi-seal 15 of a resilient material such as rubber which has a series of grooves in which spring rigs 16 are located. The seal 15 is clamped to the internal surface of the shroud 11, at the end remote from the frusto-conical portion 6 by a pair of clamping rings 17.

The seal on the driving unit comprises an annular sealing ring 29 of a resilient material such as rubber which is mounted on clamping rings 31 which are adapted to be fitted on the spigot 28. The said spigot is provided with a step between a tapered portion and a cylindrical portion and a washer 32 is fitted on the cylindrical portion to butt against the step.

The washer 32 is followed by a support ring 33 which in turn is followed by the clamping rings 31 which hold the sealing ring 29 between them. A clamp 34 is then fitted over the end of the cylindrical portion of the spigot 28 and is secured thereto by suitable means.

Mounted on the support ring 33 are a pair of flanged supporting rigs 35 which define between them a groove for the reception of a washer 36 of a suitable resilient material such as rubber.

The seals 15 and 29, 36 are so arranged that they are slightly compressed by the pipe 30 when said pipe is inserted between them as shown in the drawings. The leading end of the pipe is not gripped by the casing or by the driving unit but is advanced by exerting a force on its trailing end by a suitable hydraulic or pneumatic insertion machine (not shown).

The pneumatic lines for operating the mole are led back through the replacement pipe to the initial point at which the pipe replacement commenced. This will normally be a pit which is excavated at one end of a length of pipe which is to be replaced. Finally, the clamp 34 on the spigot 28 is provided with bores 37 for securing a cable (not shown) which is led back through the replacement pipe with the pneumatic lines to the insertion machine.

To facilitate introduction of the driving unit and the casing into an existing pipe, the probe 21 is provided with a coupling 19 which is secured to the probe by a pin 38 and to which is attached a cable 18 leading to the far end of the length of pipe which is to be replaced at which the cable is wound on a winch: rhis cable not only serves to guide the driving unit when said unit is advanced through the existing pipe in the forwards direction, but it can also serve to guide the driving unit through the replacement pipe if the unit has had to be withdrawn for any reason from the pipeline by the withdrawal mechanism.

In operation, the probe 1 is inserted into the end of a pipe 40 which it is desired to replace until the ribs 7 on the frusto-conical portion 6 abut the end of the pipe. The cable 18 is connected to the probe 21 and leads through the existing pipe to the winch (not shown) at the other end of the pipe. The leading end of the replacement pipe is inserted between the driving unit and the casing 11 as shown in the drawing and the mole 20 is activated. Operation of the mole will cause the impact surface 22 of the nose member 23 to impart a succession of impacts on the impact surface 9 of the frusto-conical portion 6 which will drive said portion into the existing pipe 40. The ribs 7 will crack the pipe and the cracked pipework will be forced radially outwardly into the surrounding soil.At the same time, the replacement pipe will be forced along the bore formed by the apparatus and in this connection it will be noted that the casing 11 is of larger diameter than the replacement pipe 30. This means that there should be a slight clearance between the pipe 30 and the newly-formed bore so that friction forces between the pipe and the wall of the bore should not arise. The cable 18 is kept taut during operation to prevent recoil of the mole and to maintain the surfaces 9 and 22 in contact with one another.

The probe 1 is desirably provided with an internal bore. The advantage of this is that, if the replacement of an existing pipe has to be stopped for any reason, for example for servicing of the mole or to permit periodically flow through the pipe to release pressure on diversion systems during peak flow periods, the driving unit can be withdrawn through the replacement pipe while the outer casing is left in place. Since a seal 15 is provided between the casing and the replacement pipe, the pipeline can still be used until operations again commence by reintroducing the driving unit.

The driving unit may be retracted by providing the mole with a conventional reversible drive mechanism. However, if the mole should break down, this mechanism will not operate.

It is then that the provision of the cable which is attached to the spigot 28 at the rear end of the mole 20 proves to be particularly useful because the driving unit can simply be drawn through the replacement pipe by means of the cable which is attached to the insertion machine. This machine is then operated in reverse to withdraw the mole while leaving the replacement pipe in position.

The apparatus according to the invention is preferably provided with an automatic conrol system such as that shown diagrammatically in Fig. 2 of the drawings. A first micro-switch 41 is located on a rearwardly tapering portion 39 of the nose member 23 of the driving unit and a second micro-switch 42 and a third micro-switch 43 are located on the main body portion of the mole 20. A fourth micro-switch 44 is located on the spigot 28 at the rear end of the driving unit behind the sealing ring 29.

The micro-switches are connected to control means for operating a valve 45 located in the pneumatic line supplying compressed air to the mole. The arrangement is such that the switch 41 is only in the "on" position when the nose member 23 of the driving unit is correctly located within the frusto-conical por tion of the outer casing. The switch 42 is only in the "on" position when the leading end of the pipe 30 is located over it. The switch 43 is also only in the "on" position when the pipe 30 is located over it. The control means will only operate to open the valve 45 to allow compressed air to be supplied to the mole when all of the switches 41 to 44 are in the "on" position and the air supply is within the required pressure range.If any of the switches 41, 43 or 44 is in the "off' position, the valve 45 is moved to the closed position to prevent operation of the mole.

Thus, if the driving unit advances the casing too far ahead of the replacement pipe, the switch 43 will move to the "off" position and will prevent further operation of the mole until the leading end of the pipe is again located over the switch 42. Similarly, if the driving unit is not correctly located in the frusto-conical portion 6 of the casing, the mole cannot be operated because the switch 41 is in the "off" position.

The switch 44 constitutes an emergency "cut-off" switch and will normally always be in the "on" position. However, if the leading end of the pipe 30 is not located over this switch, it will move to the "off" position to prevent further operation of the mole. In this case, the leading end of the pipe 30 will no longer be located over the seal 29 and will be about to part contact with the outer seal 15.

The driving unit must therefore be withdrawn and the switch 44 must be re-set manually.

Other operating combinations are possible and remote sensing arms (not shown) may be necessary where there is inadequate space between the driving unit and the pipe.

It will be seen that by means of the automatic control means above-described, it is possible to co-ordinate the rate of insertion of the replacement pipe with the rate at which the driving unit advances the outer casing.

Moreover, the apparatus according to the invention permits relative rotational and axial movement to take place between the replacement pipe on the one hand and the driving unit and outer casing on the other hand so that the pipe is not subjected to impact stresses from the driving unit but can be steadily and progressively advanced by a force exerted on the rear or trailing end of the pipe.

The outer casing is desirably made of three separable parts, as shown in the drawings, in order that it can be dismantled and removed from a confined space such as an inspection pit or an existing manhole.

The invention is not restricted to the abovedescribed embodiments but modifications and variations may be made without departing from the scope of the invention.

Claims

1. Apparatus for use in underground pipe replacement, said apparatus comprising an outer casing having a probe which is adapted to fit into an existing pipeline, a frusto-conical portion leading from one end of the probe and having a smaller end having substantially the same diameter as the outer diameter of the probe and a larger end having a diameter which is greater than that of the existing pipeline, and a cylindrical portion leading from the larger end of the frusto-conical portion and having substantially the same diameter as said larger end; a driving unit including an impact mole located within said outer casing and spaced from the cylindrical portion thereof, the space between the driving unit and the cylindrical portion of the casing being adapted to receive the leading end of a replacement pipe; means for forcing the pipe through a bore created by the outer casing, said means acting on the trailing or rearward end of the pipe; and means for withdrawing the driving unit from the casing through the replacement pipe, said withdrawing means comprising a cable or like means attached to the rear end of the driving unit, passing through the replacement pipe and attached to drive means beyond the trailing or rearward end of the said replacement pipe whereby the driving unit can be withdrawn from the outer casing while leaving said casing in situ.

2. Apparatus according to claim 1, wherein sealing means are provided between the cylindrical portion of the casing and the leading end of the replacement pipe and between the driving unit and the said leading end of the replacement pipe.

3. Apparatus according to claim 2, wherein the sealing means take the form of annular seals located in grooves in, or clamped to, the casing and the driving unit.

4. Apparatus according to any preceding claim, wherein the driving unit comprises an impact mole having a probe and a frusto-conical nose member mounted on its front end and a partially-tapered cylindrical spigot mounted on its rear end.

5. Apparatus according to claim 4, wherein the spigot is provided with means for attaching thereto a cable or the like.

6. Apparatus according to any preceding claim, wherein automatic control means are provided for co-ordinating the rate at which the replacement pipe is advanced with the drive of the driving unit, said means permitting relative rotational and axial movement between the casing and driving unit on the one hand and the replacement pipe on the other hand while preventing separation of these components during operation of the apparatus.

7. Apparatus according to claim 6, wherein the automatic control means comprise at least one microswitch arranged to control the operation of a valve located in a pneumatic line leading to the mole.

8. Apparatus according to any preceding claim, wherein the probe comprises a tubular member connected at or adjacent to one end to the frusto-conical portion and having a nose cone secured to its other end.

9. Apparatus according to claim 8, wherein the outer surface of the probe is provided with a series of circumferentially-spaced upstanding ribs.

10. Apparatus according to claim 8 or claim 9, wherein the probe is connected to the frusto-conical portion by a screw-threaded connection.

11. Apparatus according to claim 10, wherein a series of balls of nylon or like material are located in a recess in said screwthreaded connection.

12. Apparatus according to any preceding claim, wherein the outer surface of the frustoconical portion is provided with a series of circumferentially-spaced upstanding ribs.

13. Apparatus according to any preceding claim, wherein the frusto-conical portion is provided with a tapered abutment surface arranged to be engaged by the driving unit.

14. Apparatus for use in underground pipe replacement substantially as described herein with reference to the drawings.