AU779022B2 - The replacement of underground pipe - Google Patents

Description

r -1- Regulation 3.2

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

(ORIGINAL)

Name of Applicant: ROWLAND'S UNDERGROUND TECHNOLOGY PTY.LTD.

Actual Inventors: Address for Service: *I Invention Title: DAVIES COLLISON CAVE, Patent Attorneys, 1 Little Collins Street, Melbourne, 3000.

The replacement of underground pipe Details of Associated Provisional Application(s) No(s): PP9293/99 filed 18 March, 1999 The following statement is a full description of this invention, including the best method of performing it known to us: Q:\OPER\RSH\PP9293-9.061 2/3/0 P:\OPER\RSH\PP9293-9.SPE 25/0 -2- THE REPLACEMENT OF UNDERGROUND PIPE The present invention relates to the replacement of underground pipe and more particularly to the removal of an existing pipe to form a void within the ground to receive a new pipe.

One technique for the replacement of existing underground pipe for a utility such as mains water involves passage of a reaming or cutting unit through the existing pipe in order to break the existing pipe into small pieces. A void remains within the soil in the area previously occupied by the pipe whereby a new pipe can be drawn into that void as the existing pipe is progressively destroyed. Breakage of the existing pipe into smaller pieces S. may be accompanied by a flushing action using water in order to flush pipe debris to a convenient position where it can easily be removed, for example through a removal pit dug into the ground. Although some pipe debris can be removed by flushing, inevitably some debris will remain and is likely to be displaced into the surrounding soil.

S: The above procedure can work quite satisfactorily when the existing pipe is made of clay. However a particular difficulty arises when the existing pipe is of asbestos cement that is as a cement reinforced with asbestos fibres. In the past, a.c. mains water pipes have been widely used as distributor pipes by water authorities. When these water pipes are due for replacement current regulations in many municipalities require removal of the existing pipe in such a manner that the surrounding ground is virtually free from contamination by asbestos. Hitherto, breakage of the pipe using the technique discussed previously has not been satisfactory for a.c. pipe as a significant amount of asbestos residue remains in the surrounding soil after breakage of the pipe even if breakage is accompanied by flushing. As a result of this, the current practice for removal of a.c. pipe is to dig a trench from ground level to expose the underlying a.c. pipe and then to remove the pipe via that trench in order to ensure complete removal of the existing pipe. While removal of the existing a.c. pipe through the trench ensures that the ground is substantially free from asbestos contamination, this technique is time-consuming and expensive.

P:OPERSotm.d-2p.doc.- Ili 104 -3- According to the present invention, there is provided a method for removing underground pipe comprising the steps of pulverising the pipe in the presence of a liquid, and mixing the pulverised material with the liquid to form a slurry for subsequent removal, wherein the pulverisation and mixing of the pipe material is effected by a rotating pulveriser which is drawn along the existing pipe, the pulveriser having cutting teeth and mixing means separate from the teeth to form the slurry by mixing and to densify the slurry.

Advantageously, the existing pipe is cement pipe reinforced with asbestos fibres and the existing pipe is pulverised into a powder which is mixed with the liquid to form a thick slurry of paste-like consistency in which the asbestos fibres are bound.

Advantageously, a replacement pipe is drawn behind the pulveriser into the void formed within the ground by the action of the pulveriser.

Further according to the present invention, there is provided a rotary pulveriser for use in a method according to any one of claims 1 to 7, said pulveriser having teeth for cutting and pulverising the pipe material into powder form in the presence of liquid, and :'means separate from the teeth for mixing the pulverised pipe material with the liquid to form S* a thick densified slurry.

°*oee In a preferred embodiment of the invention, the pulveriser is subject to a rotational drive and is adapted for connection at a forward end to a drill rod within the existing pipe whereby the pulveriser can be drawn along the pipe by drawing the drill rod from a drilling rig on the surface.

Advantageously, the pulveriser comprises an axially-extending body having cutter teeth at a forward end portion of the body to engage an end of the pipe and to cut the pipe progressively from that end and to comminute into powder form the material forming the pipe, and mixing blades mounted on the body rearwardly of the cutter teeth to mix the comminuted material with the liquid to form the slurry which is discharged rearwardly from the rearward end of the pulveriser.

P:\OPER\RSHPP9293-9.SPE 2/3/00 -4- Preferably, the body of the pulveriser is of tubular form to receive a flow of said liquid via said drill rod, the liquid being discharged from said tubular body via jets which are preferably positioned adjacent the teeth and the mixing blades.

Advantageously, there are a plurality of sets of cutting teeth axially spaced along said body and of progressively increasing cutting diameter.

Advantageously, the mixing blades are configured to cause the slurry to discharge rearwardly of the pulveriser and to direct the slurry inwardly into a zone adjacent the body in order to densify the slurry.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:- Figure 1 shows schematically a method for pipe removal and replacement using a pulveriser in accordance with a preferred embodiment of the invention; :..•*Figure 2 is an enlarged view showing in greater detail the pulveriser used in the method of Figure 1; and Figure 3 is a schematic transverse section taken through the pulveriser to better .0 S-illustrate the configuration of mixing blades of the pulveriser.

In accordance with the broad principles of the invention, existing underground pipe, particularly a.c. pipe, is pulverised to a fine powder and mixed with liquid to form a slurry which flows to a collection pit for subsequent removal.

As shown schematically in Figure 1, a drill rod 2 of a directional drilling rig 4 mounted at ground level is inserted through a length of pipe 6 to be removed and replaced.

The remote end of the drill rod 2 is coupled to the leading end of a pulveriser 8 which will be described in detail later. The trailing end of the pulveriser 8 is coupled to the leading end of a new pipe 10. The drilling rig 4 is operated to draw the drill rod 2 through the existing pipe 6 in a rearwards direction, in other words a direction opposite to that in which the drill rod was inserted into the existing pipe. At the same time the drill rod 2 is rotated. The P:\OPER\RSH\PP9293-9.SPE 23/00 rotation and drawing motion of the drill rod 2 causes the pulveriser 8 to be rotatably driven and displaced with the drill rod 2 so that cutting teeth on the pulveriser 8 cut the existing pipe 6 into fine powder. Water or other liquid is fed through the drill rod 2 to the pulveriser 8 in order to cool the cutting teeth and to mix with the powder to form a slurry. By way of illustration only, the rotational speed of the pulveriser is about 200 rpm.

The pulveriser 8 not only breaks the existing pipe 6 into powder form but also cuts into the surrounding ground a hole of larger diameter than that of the existing pipe 6. The leading end of the replacement pipe 10 is coupled to the trailing end of the pulveriser 8 and is drawn into the hole thus formed as the pulveriser 8 is drawn by the drill rod 2. The new pipe 10 drawn by the movement of the pulveriser 8 is itself of a diameter less than the diameter of the hole formed by the pulveriser so that a passage 12 is formed between the outer surface of the new pipe 10 and the wall of the hole. The slurry formed by the mixture of powder and water or other liquid passes along the passage 12 externally of the new pipe into a collection pit 14 dug at a suitable location. The slurry can then be removed from the -pit 14 by suction, for example using a vehicle similar to that used for emptying septic tanks and the like, and the slurry can then be transported by that vehicle to a suitable site for safe disposal. It is to be noted that the coupling between the leading end of the new pipe 10 and the trailing end of the rotating pulveriser 8 is a swivel coupling which permits the pulveriser 8 to rotate relative to the new pipe 10 and which also plugs the leading end of the new pipe to ensure that slurry and other debris does not enter the new pipe As shown in greater detail in Figures 2 and 3, the pulveriser 8 comprises a tubular body 20 having at its forward end a threaded coupling 22 for connection to a complementary coupling at the end of the drill rod 2. Water or other liquid is pumped under relatively high pressure through the drill rod 2 into the interior of the tubular body 20 via the threaded coupling 22, the liquid being discharged from the body 20 via a series of jets 24 which will be described later. At its rear end, the tubular body 20 is closed and carries a pulling eye 26 to which is attached a swivel caapg which is connected to the leading end of the new pipe 10. At its forward end portion, the body 20 carries sets of cutting teeth 28 of progressively increasing diameter. Each set of teeth consists of teeth angularly spaced around the axis of P:\OPERRSH\PP9293-9.SPE 23/00 -6the tubular body 20, each tooth consisting of a block 30 which extends axially of the body the block 30 having a recess at its leading end and into which is deposited a thick layer 32 of wear-resistant material, for example tungsten carbide applied in a solder. This thick layer 32 of wear-resistant material forms the cutting tip of the tooth and lies at the forward end of the leading flank of the tooth (as considered in the direction of rotation of the pulveriser) and also at the leading axial end face of the tooth as considered in the direction of movement of the pulveriser as the pulveriser is drawn by the drill rod 2.

In the embodiment shown, there are three such sets of teeth (designated as 28a, 28b, 28c) which, as previously stated, are of progressively increasing diameter. The first or leading set of teeth 28a are of an outer diameter greater than that of an existing pipe 6 of smaller diameter with which the pulveriser 8 is to be used, the inner diameter of these teeth which corresponds to the diameter of the tubular body 20 being less than the internal diameter of the existing pipe 6. Accordingly this set of teeth engages the end edge of the existing pipe and effectively grinds and pulverises that edge as the pulveriser is advanced.

The jets 24 are carried by the tubular body 20 in positions adjacent to the cutting tips of the teeth so that the liquid cools the tips and also prevents clogging of the wear-resistant material and also forms the basis for the slurry which will be formed by intimate mixing of the powder and liquid. It is unlikely that the first set of teeth 28a alone will break all of the pipe material down into powder form. Instead, it is likely that the first set of teeth 28a will break the pipe material down into a mixture of small chunks and powder. However the action of the subsequent sets of teeth 28b, 28c is to comminute all of the pipe material into powder form. Also these further sets of teeth progressively enlarge the hole previously occupied by the existing pipe 6.

It is to be noted that the pulveriser 8 can also be used with larger diameter pipe, in which case the second set of teeth 28b may form the primary teeth for contact with the end edge of the pipe, the third set of teeth 28c then ensuring that the pipe material removed by the second set is fully broken down into powder form.

P:\OPER\RSH\PP9293-9.SPE 2/3/00 -7- Although the action of the sets of cutting teeth 28 will cause some mixing of the powder with the water or other liquid discharged adjacent the zone of the teeth, a set of mixing blades 34 is formed on the tubular body 20 behind the sets of cutting teeth 28 in order to ensure that the powder and liquid is mixed into a dense slurry prior to discharge from the pulveriser 8. The mixing blades 34 extend generally longitudinally of the tubular body with the axis of the blades 34 being inclined at an angle relative to the longitudinal axis of the tubular body, for example about 100, with the inclination of the blades being in such a direction in relation to the direction of rotation of the pulveriser 8 that rotation of the blades will drive the slurry rearwardly relative to the pulveriser. As shown schematically in Figure 3, the leading flank of the mixing blades 34 as considered in the direction of rotation is inclined inwardly relative to a radial plane so that the rotation of the mixing blades 34 as the pulveriser 8 rotates not only acts to displace the slurry rearwardly out of the pulveriser but also forces the mixture of powder and liquid inwardly into a smaller volume within the zone of action of the mixing blades 34 to densify the slurry to ensure that a thick slurry is formed.

The general configuration of the mixing blades 34 is clearly shown in Figure 2 from which can be seen that the interior edges of the blades 34 are spaced from the tubular body 20 to define within the array of blades 34 an interior open zone 36 through which the thick slurry can flow.

The leading flank and outer flanks of the mixing blades 34 are also faced with a wearresistant material 38, for example tungsten carbide applied in a solder, and jets 24 discharge from the interior of the tubular body 20 adjacent these flanks.

Although the primary function of the mixing blades 34 is to ensure that mixing takes place to a sufficient extent to form a dense slurry, these blades 34 may also cause further comminution of the pipe material. Also, these blades may act to effect final sizing of the hole for the new pipe 10 being drawn in by the pulveriser. The surrounding soil removed as a result of this final sizing is drawn into the zone 36 within the blades 34 to be mixed with the slurry and then discharged.

Advantageously, the jets 24 which are provided around the circumference of the P:\OPER\RSH\PP9293-9.SPE 2/3/00 -8tubular body 20 at positions adjacent the operative faces of each of the teeth and mixing blades are replaceable by jets of different size to permit improved control particularly as regards the density of the slurry. Preferably two such jets are associated with each of the mixing blades.

The slurry thus formed is of such a density that it is of a paste-like consistency which ensures that the asbestos fibres are bound within the slurry and can be safely removed. Tests have shown that approximately 95 of the asbestos will be removed by the slurry. The small quantity of asbestos which may remain within the ground is insufficient to cause environmental problems.

The embodiment has been described by way of example only and modifications are S"possible within the scope of the invention.

Throughout this specification, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers.

Claims (16)

1. A method for removing underground pipe comprising the steps of pulverising the pipe in the presence of a liquid, and mixing the pulverised material with the liquid to form a slurry for subsequent removal, wherein the pulverisation and mixing of the pipe material is effected by a rotating pulveriser which is drawn along the existing pipe, the pulveriser having cutting teeth and mixing means separate from the teeth to form the slurry by mixing and to densify the slurry.

2. A method according to claim 1, wherein the existing pipe is cement pipe reinforced with asbestos fibres and is pulverised into a powder which is mixed with the liquid to form a S: thick slurry of paste-like consistency in which the asbestos fibres are bound.

3. A method according to claim 1 or claim 2, further comprising drawing a replacement pipe behind the pulveriser into the void formed within the ground by the action of the pulveriser.

4. A method according to any one of claims 1 to 3, wherein the pulveriser is operative to cut into the surrounding ground a hole of larger diameter than that of the existing pipe.

A method according to any one of claims 1 to 4, wherein the pulveriser is operative to cause discharge of the slurry rearwardly relative to the direction of advance of the pulveriser for collection in a pit within the ground.

6. A method according to any one of claims 1 to 5, wherein the mixing means is operative to densify the slurry by forcing the mixture of pulverised material and liquid from a larger volume zone of the mixing means into a smaller volume zone of the mixing means, with said densified slurry being discharged from the pulveriser for subsequent removal. P.OPER\RSWrolStH n2sp4doc.-II 11/04

7. A method according to any one of claims 1 to 6, wherein a forward end of the pulveriser is connected to a drill rod within the existing pipe and the pulveriser is drawn along the existing pipe by drawing the drill rod from a drilling rig.

8. A rotary pulveriser for use in a method according to any one of claims 1 to 7, said pulveriser having teeth for cutting and pulverising the pipe material into powder form in the presence of liquid, and means separate from the teeth for mixing the pulverised pipe material with the liquid to form a thick densified slurry.

9. A pulveriser according to claim 8, wherein the pulveriser is adapted to be rotatably driven by connection at a forward end to a drill rod within the existing pipe whereby the pulveriser can be drawn along the pipe by drawing the drill rod from a drilling rig.

10. A pulveriser according to claim 8 or claim 9, wherein the pulveriser comprises an axially-extending body having cutting teeth at a forward end portion of the body to engage an end of the pipe and to cut the pipe progressively from that end and to comminute into powder form the material forming the pipe, and the mixing means comprise mixing blades mounted on the body rearwardly of the cutting teeth to mix the comminuted material with the liquid to form the slurry which is discharged rearwardly from a rearward end of the 20 body.

11. A pulveriser according to claim 9 and claim 10, wherein the body of the pulveriser is of tubular form to receive a flow of said liquid via said drill rod, the liquid being discharged from said tubular body via jets.

12. A pulveriser according to claim 11, wherein the jets are positioned adjacent the teeth and the mixing blades.

13. A pulveriser according to any one of claims 10 to 12 having a plurality of sets of said cutting teeth axially spaced along said body and of progressively increasing cutting diameter. P.)PER\KRSH\mlDd- I 11

14. A pulveriser according to claim 10 or any claim dependent on claim 10, wherein the mixing blades are configured to cause the slurry to discharge rearwardly of the pulveriser and to direct the slurry inwardly into a zone adjacent the body in order to densify the slurry.

A method for removing underground pipe substantially as hereinbefore described with reference to the accompanying drawings.

16. A pulveriser for removing underground pipes substantially as hereinbefore described with reference to the accompanying drawings. DATED this 2 8 th day of October 2004 S: ROWLAND'S UNDERGROUND TECHNOLOGY PTY LTD S by their Patent Attorneys o DAVIES COLLISON CAVE *0* 0 o**o