GB2130625A

GB2130625A - Driving tunnels

Info

Publication number: GB2130625A
Application number: GB08331101A
Authority: GB
Inventors: Dieter Stuckmann; Jurgen Hein
Original assignee: Gewerkschaft Eisenhutte Westfalia GmbH
Current assignee: Gewerkschaft Eisenhutte Westfalia GmbH
Priority date: 1982-11-27
Filing date: 1983-11-22
Publication date: 1984-06-06
Also published as: IT8312675A1; ATA385783A; ES527554A0; CS246069B2; DE3244040A1; SU1329624A3; FR2536787A1; DE3244040C2; AT378238B; GB2130625B; IT8312675A0; JPS59106639A; ES8501474A1; GB8331101D0; FR2536787B1; IT1195480B

Abstract

A knife shield 6 is used for driving a tunnel 5 around and along a buried main drain 1 for use in restoring or repairing the main drain, the main drain having lateral feeder drains 3 leading thereinto. The knife shield 6 has a plurality of elongate knives 8 and 10 arranged side-by-side on a support frame 7. The knife shield 6 is open- bottomed. The knife shield 6 is provided with a connector pipe 22 which can be used as part of an indirect connection between a feeder drain 3 and the main drain 1. The connector pipe 22 is positioned within one of the knives 10 of the knife shield 6, and is movable longitudinally relative to that knife, so that the knife shield can be advanced relative to the connector pipe without breaking the indirect connection between a feeder drain 3 and the main drain 1. <IMAGE>

Description

SPECIFICATION Method of, and apparatus for, driving a tunnel This invention relates to a method of, and apparatus for, driving atunnel around and along a buried main pipe for use in restoring or repairing the main pipe, the main pipe having lateral branch pipes leading thereinto. The invention is particularly concerned with restoring or repairing main drains, which have feeder drains leading from individual houses connected thereto.

In orderto repair or restore a buried main drain, it is well known to drive a small arcuate tunnel around and along the main drain. During the driving of the tunnel, the main drain is replaced in sections by a temporary plastics drain, into which the feeder drains are temporarily diverted. Afterthe tunnel has been driven, the new main drain is laid, the feeder drains are connected, and the tunnel is filled with, for example, special concrete, or earth. The tunnel roof support means, which is introduced during the tunnelling operation, and takes the form of arches and support plates, is left in the earth as disposable equipment.

The known tunnelling method is disadvantageous because of the irregular spacing ofthe house feeder drains. During diversion, these feeder drains can be allowed to remain out of operation for only a short period (for example approximately 15 minutes), and the known tunnelling method does not always permit this requirement to be met.

The aim of the invention is to provide an improved method of, and apparatus for, driving a tunnel along a buired main pipe provided with lateral feeder pipes.

The present invention provides a method of driving atunnel around and along a buried main pipeforuse in restoring or repairing the main pipe, the main pipe having lateral branch pipes leading thereinto, wherein the tunnel is driven using an open-bottomed knife shield, the knife shield having a plurality of elongate knives arranged side-by-side on a support frame, and wherein, whenever a branch pipe is encountered by the advancing knife shield the direct connection between that branch pipe and the main pipe is replaced by an indirect connection, the indirect connection including a connector pipe which passes through the knife shield.

Advantageously,theconnectorpipeis movable longitudinally relative to the knife shield, so that the knife shield can be advanced beyond an encountered branch pipe without breaking the indirect connection between that branch pipe and the main pipe.

Preferably, the knives of the knife shield are advanced by means of double-acting rams which act between the supportframe and an abutment frame positioned behindthesupportframe.

The knives may be provided with rearwardlyextending tail extensions, and roof support means may be fitted in the shield hood formed by said tail extensions. Advantageously, the roof support means is constituted by longitudinally-spaced arches and support plates, and the support plates are driven in between the arches and the surrounding earth by retracting the abutment frame.

Thus, in orderto drive a tunnel around and along a main drain, use is made of a small arcuate knife shield, within the protection of which the tunnelling work is carried out, and the knives ofwhich can be advanced, either individually or in groups, preferably by means of the abutment frame. The knife shield is open at the bottom, so that a main drain can be replaced in sections by a temporary plastics pipe, by means of which discharge of waste water is maintained during replacement. When, during the course oftunnelling, the knife shield encounters a house feeder drain, the latter is joined to the temporary plastics pipe by way of the connector pipe, so that the house feeder drain can remain in operation during furtherformation ofthe tunnel.When a house feeder drain is joined unto the connector pipe, the knife shield can be advanced further, relative to the connector pipe, so that lengthy stoppage times can be avoided. When the shield is advanced further, the front end of the connector pipe (which is still joined to the house feeder drain) projects rearwardlyfrom the knife shield. The house feeder drain can then be separated from the connector pipe and, attached to the temporary plastics pipe, after which the connector pipe can be used again. Thus, the house feeder drain is temporarily joined to the plastics pipe, until the knife shield has been advanced past that feeder drain.

The invention also provides a knife shield for driving a tunnel around and along a buried main pipe for use in restoring or repairing the main pipe, the main pipe having lateral branch pipes leading thereinto, the knife shield having a plurality of elongate knives arranged side-by-side on a supportframe, and the knife shield being open-bottomed, wherein the knife shield is provided with a connector pipe which can be used as part of an indirect connection between a branch pipe and the main pipe, the connector pipe passing through the knife shield, and being movable longitudinally relative to the knife shield, so thatthe knife shield can be advanced relative to the connector pipe without breaking the indirect connection between a branch pipe and the main pipe.

Preferably, the knife shield further comprises an abutmentframe positioned behindthesupportframe, the abutmentframe being connected to the support frame by means of double-acting rams.

In a preferred embodiment, the knives ofthe knife shield are hollow, and the connector pipe is displaceably arranged within one ofthe knives. Preferably, the connector pipe is arranged within one ofthe bottom (floor-contacting) knives of the knife shield. Conveniently, the connector pipe is constituted by a hollow beam.

Advantageously,theoutwardly-facing surface of said one knife is provided with a longitudinal slot, and the connector pipe extends substantially the entire length of said one knife.

The connector pipe may be provided with first and second connection portions at opposite ends thereof.

In this case,the shield mayfurthercompriseaddition- al pipes for connecting the first connection portion of the connector pipe to the main pipe, and for connecting the second connection portion of the connector pipe to a branch pipe. Preferably, the second connection portion extends outwardly, and is aligned with the longitudinal slot in said one knife.This enables the additional pipe joining the connector pipe to a branch pipe to move along the slot in said one knife, as that knife is subsequently advanced.

Advantageously, the major portion of the connector pipe is off-set back from the outersurface ofthe knife shield so that, when the connector pipe is moved to the rear of the knife shield, the connector pipe is spaced from the wall of the tunnel by a distance which is sufficient to permit the erection of arcuate roof support means to the rear ofthe knife shield.

Preferably, the rear end portion of the hollow beam constitutes a widened guide head, the guide head being sized to make sliding contact with the interior of said one knife, and the remaining portion of the beam constituting said off-set portion. Conveniently, the second connection portion is arranged within the guide head.

Advantageously, the connector pipe is provided with a retaining memberwhich can be used to fix the connector pipe within the tunnel. Preferably, an anchoring ring constitutes the retaining member.

Conveniently, the connector pipe is provided with means for detachably fixing the connector pipeto said one knife.

Advantageously, the front end of the connector pipe is formed with an inclined edgefordeflecting earth present in said one knife into the interior of the knife shield. Also the front end of the connector pipe may be provided with a rotatable sharp edgefor cleaning the internal walls of said one knife.

If branch pipes are present on both sides of the main pipe, collector pipes can be arranged at both sides of the knife shield. Preferably, in this case, the support frame of the knife shield is displaceably supported at both bottom side edges on a respective bottom knife, and each bottom knife accommodates a connector pipe, each connector pipe passing through the knife shield and being movable longitudinally relative to the knife shield.

Where a tunnel is being driven through relatively resistant earth, the or each connector pipe may constitute one of the knives ofthe knife shield. In this arrangement, the width of such a knife can be less than that ofthe other knives ofthe shield, so that, when that knife is advanced, an excessively large gap is not created.

The invention will now be described in greater detail by, way of example, with reference to the accompanying drawings, in which:~ Fig. 1 is a transverse cross-section oftunnel driving apparatus constructed in accordance with the invention, the apparatus being shown in a tunnel driven in the direction in which a main drain is laid; Fig. 2 is a vertical longitudinal cross-section of the tunnel driving apparatus of Fig. 1; Fig. 3 is a plan view of the two bottom knives ofthe tunnel driving apparatus of Fig. 1; Fig. 4 is a cross-section taken on the line IV-IV of Fig.

1, and shows one of the bottom knives; Fig. 5 is a cross-section taken on the line V-V of Fig. 1, and shows one of the bottom knives; Fig. 6 is a plan view of the knife of Fig . 5; Fig. 7 is a plan view of one of the hollow beams arranged within the two bottom knives; and Figs. 8to 13 illustrate, diagramatically, the tunnel driving apparatus of Figs. 1 and 2 at various working stages during the driving of a tunnel, Figs. 8, 10 and 12 showing the tunnel in cross-section, and Figs.9,11 and 13 each showing a plan view of one of the bottom knives of the apparatus.

Referring to the drawings, Fig 1 shows a main drain 1 which is buried in the earth, and rests on a concrete base 2. Feeder drains 3, which lead to houses, are joined to the main drain 1 by way of connecting pipes 4. In orderto restore or repairthe main drain 1, for example by replacing sections thereof, an arcuate tunnel 5 of small cross-section is driven in the direction in which the main drain is laid. This tunnel 5 is driven using a small open-bottomed knife shield 6.

The knife shield 6 has a rigid arcuate support frame 7 which supports a plurality of elongate members (knives) 8. The knives 8 are arranged side-by-side parallel to the axis ofthetunnel 5, and form a ogival shield within the protection of which the tunnelling operations are carried out. The knives 8 are guided on the frame 7 for movement in thetunnelling direction T by means of T-shaped guides 9. The frame 7 is braced againstthetwo side walls ofthetunnel 5. The frame 7 is mounted on a pair of bottom knives 10, each of which is constituted by a heavy beam of box-shaped cross-section. The knives 10 are guided on the lower ends oftheframe 7, by means ofT-shaped guides 9.

Each of the knives 8 has a rearward (tail) extension 11, thetail extensionstogetherforming ashieldtail hood, within the protection of which tunnel roof support means can be erected. The tunnel roof support means is constituted by longitudinally-spaced roof support arches 12 and support plates 14. The arches 12 are underpinned by concrete or steel blocks 13. The support plates 14 are fitted between the arches 12 and the surrounding earth,the support plates being of roughlyW-shaped cross-section.

An abutmentframe 15 is positioned to the rear of thesupportframe7,theabutmentframe being connected to the supportframe bythree doubleacting hydraulic rams 16 (see Fig. 2). As shown in Fig.

1, one ram 16 is provided atthe apex ofthe support frame 7, and one at each of the two feet of the support frame. The cylinders ofthe rams 16 are pivoted to the supportframe 7 at 17, and their piston rods 18 are pivoted to the abutment frame 15 at 19.

Each of the knives 8 and 10 can be coupled to the frame 15. This is achieved, in a known manner, by means of bolts 20 which can be introduced into holes 21 formed in the knives 8 and 10. A row of such bolt holes 21 is provided on each ofthe knives 8 and 10; and the holes within each row are spaced apart by distancesthatare considerably smallerthan the working stroke ofthe rams 16. The relatively narrow spacing of the holes 21 in each of the knives 8 and 10, permits one or more knives to have a reduced working stroke when the knife shield 6 encounters a feeder drain 3 during the driving ofthetunnel 5.

During normal tunnelling, the knives 8 are con- nected individually, or in groups, to the abutment frame 15 by the bolts 20; and are then urged forward (that is to say in the tunnelling direction T)together with the abutmentframe by extending the rams 16.

The bolts 20 are then released, and the abutment frame 15 is retracted by retracting the rams 16.

Another knife 8f another group of knives 8, can then be advanced in a like manner. As soon as all of the knives 8 have been advanced in the direction ofthe arrow, the two kn knives 10 are advanced, togetherwith the abutmentframe 15 in the same way. The support frame 7 can then be advanced by extending the rams 16, the abutmentframe 15 acting as an abutment for this advance movement. In this case, the abutment frame 15 isfixed to all oftheknives8 and 10 by the bolts 20, so that the reaction forces of the rams 16 are absorbed bythesurrounding earth via the knives.

As tunnelling proceeds, the main drain 1 can be repaired or replaced, in sections, in the known manner. As a new section is laid, waste water connection is maintained by a temporary plastics connection pipe (not shown), which maintains the connection between the newly laid main drain section and the next section ofthe main drain.

A respective hollow beam 22 is arranged in each of thetwo knives 10. Each ofthe beams 22 constitutes a pipe, and extends substantially the entire length ofthe associated knife 10. The construction ofthe knives 10 and ofthe hollow beams 22 can be seen best in Figs. 4 to 7. The upperfaces of the bottom knives 10 have T-shaped attachments 23 wherebytheyare guided in complementaryundercutchannels provided atthe bottom ends ofthe supportframe 7. These parts form the T-shaped guides 9 referred to above. The front ends of the bottom knives 10 areformed aswedge- shaped cutting edges 24. The hollow beams 22 can be introduced, from the rear, into the knives 10.The foward end portion of each beam 22 constitutes a guide head 25, the guide heads being effectiveto guide the beams inside the hollow profiles of the knives 10. The end face 26 of each guide head 25 is formed as an inclined edge. The remaining portion of each beam 22 (that isto saythe portion to the rear of its guide head 25) is tubular. Each ofthe hollow beams 22 defines a channel which extends from a rear opening 27to afrontopening 28, thefront opening lying directly to the rear of the cutting edge 26 and on the side ofthe guide head 25. The knives 10 each have a slot 29 on the sidethereoffacing the adjacent side wall ofthetunnel 5.The slots 29 extend substantially the entire length of the knives 10, so that the front openings 28 ofthe hollow beams 22 are aligned therewith.

During normal tunnel-driving operations, the two hollow beams 22 are pushed completely into the knives 10. The beams 22 arefixedtotheknives 10 by releasablebolts30,sothat,whentheknives 10 are advanced, they entrain the hollow beams. When a feeder drain 3 is encountered, it is blocked off, its connecting pipe 4 is removed, a pipe bend 31 is attached to the feeder drain outside the knife shield 6, the underlying tunnelling knive (or knives) 8 is (or are) retracted, and the pipe bend 31 is extended as far as the adjacent knife 10 by means of a connecting pipe 32. The connecting pipe 32 is of single or multi-part construction.The connecting pipe 32 is then attached to the front opening 28 ofthe respective hollow beam 22 by way of a pipe bend 33, and a pipe joint 34, for example a pipe flange (see Fig. 5).

In the case of relatively resistant ground, a pipe or hose can be led, outsidethe knife shield 6, directly from the feeder drain 3 to one ofthe hollow beams 22.

On the other hand, in the case of non-resistant, for example crumbling, ground, the diversion to one of the hollow beams 22 is achieved by lengthening the feeder drain 3 in sections, as described above using the pipe parts 31 to 33.

Figs. 8 and 9 show a feeder drain 3, lying in the front ofthe knife shield 6, and its connecting pipe 4 leading to the main drain 1, and Figs. 10 and 11 showthe feeder drain connected to the adjacent hollow beam 22 via the pipe bends 31 and 33 and the connecting pipe 32. The rear opening 27 of that hollow beam 22 is connected to the main drain 1 by means of a connecting pipe 34' (see Fig. 11). For this purpose, a suitable pipe joint, for example a pipe flange, is provided atthe rear opening 27 ofthat hollow beam 22.It will be seenthatthefeederdrain 3 is then connected, via that hollow beam 22, to that part of the main drain 1 lying to the rear of the knife shield 6, so that the feeder drain can be brought into service again, and so thatthe advance ofthe knife shield 6 can then be immediately resumed.

That hollow beam 22 is then released from its knife 10 by removing the bolt(s) 30, so that, upon further advance of the shield 6, that knife 10 can be advanced without advancing that hollow beam 22. That hollow beam 22 is secured in the tunnel 5 by means of a retaining member 35 positioned at its rear end. The retaining member 35 comprises an anchoring ring 36 through which an anchor (not shown) can be driven into the floor of the tunnel. In this way, that hollow beam 22 is safely held in position when the shield 6 is advanced. When the knife shield 6 is advanced, the anchored hollow beam 22 slides rearwardly out of its knife 10. As this happens, the pipe bend 33, which is connected to the front opening 28 of that hollow beam 22, moves along the slot 29 in its knife 10.As soon as the pipe joint 34 has moved rearwardly out of that knife 10, the pipe connections 31 to 33 can be removed, and the feeder drain 3 can be rejoined directly to the main drain 1 to the rearofthe knife shield 6 by way of a connecting pipe 37 (see Figs. 12 and 13). Fig. 13 shows that knife 10 ofthe knife shield 6 following a further advance ofthetunnel 5 in the direction indicated by the arrow T. The feeder drain 3 is then located at some distance to the rear of the knife shield 6, and is joined directlytothe main drain 1. The hollow beam 22, which previously diverted waste water to the main drain 1, is completely separated from its knife 10. Then, the anchor is removed from the retaining member 35, for example, by means of a compressed air-drill, and that hollow beam is again driven into its knife 10 from the rear.

Within its front cutting edge 24, each knife 10 has a deflector plate 38 directed towards the interior of the tunnel 5 (see Fig. 6). Each knife 10 also has apertures 39 and 40 which are distributed along its length and face the interior of the shield 6, so that, when a hollow beam 22 is introduced into its knife 10, any earth that may be present in that knife is laterally displaced by the inclined end edge 26 ofthat hollow beam, and is forced out of that knifethrough the apertures 39 and 40. As soon as a hollow beam 22 is fully inserted into its knife 10, it is connected to that knife by means ofthe bolts 30. Thus, upon further advance of the knife shield 6, it is carried along with its knife 10.

In orderto erectthetunnel roofsupportmeans after the knife shield 6 has been advanced, the arches 12 are introduced into the shield tail hood, and positioned immediately behind the knife shield. The support plates 14 are then introduced from the side ofthe shield 6. As shown in Fig. 2,this can be achieved by causing the rear ends of the support plates 14 to extend beyond the most recently-positioned arch 12; and then, by retracting the abutmentframe 15 towards that arch, by pressing the support plates back until they overlap the previously-introduced support plates. The most recently positioned arch 12 is then wedged in position.

If feeder drains 3 are located at both sides of the main drain 1 (as indicated in Fig. 13 by the reference numerals 3 and 3') then the hollow beams 22 of both knives 10 are used. Obviously, if feeder drains 3 are located at only one side of the main drain 1, only one of the hollow beams 22 will be used. In this case, the other hollow beam 22 is superfluous, and can be dispensed with entirely.

As shown in Fig.7, to the rear of its guide head 25, each ofthe hollow beams 22 is laterally off-set towards the interior of the knife shield 6 to such extent that, as that hollow beam is pushed out to the rear of its knife 10, the major portion of its length is positioned at such a distance from the adjacent side wall ofthe tunnel Sthatan arch 12 can be introduced, behind the abutment frame 15, into the space between that beam and the side wall ofthetunnel.

In orderto detach and expel any dirt from the hollow interior of the knives 10 as their hollow beams are introduced, the hollow beams are each provided, at theirforward ends, with a rotating knife edge (not shown). These rotating knife edges remove contami nating material adhering to the inner walls of the knives 10, and, bywayofthe inclined end edges 26, force this material inwardly through the apertures 39 and 40 formed in the knives 10.

As an alternative to locating the hollow beams 22 in the knives 10, they could each be displaceably mounted on, or in, one ofthe knives 8. In this case too, the arrangement must be such that the diversion of wastewaterthrough the hollow beams 22 is maintained until the knife shield 6 has moved past the feeder drain 3 concerned. It is also possible for a hollow beam 22to be designed as one ofthe knives8 or 10. This arrangement is advantageous when, for example, the supportframe 7 ofthe knife shield 6 is displaceably supported at both sides on two parallel bottom knives 10. In this case, the lowermost knife 8 at each side ofthe shield 6 is oftubularform, so that it can take overthefunction of a hollow beam 22. As long as there is no attachment to a feeder drain 3, one of said lowermost knives 8, can be joined to the adjacent knife 10 by a releasable coupling to form a thrust unit. It would also be possible for one ofthe other knives 8 to be oftubularform, so that this knife can take overthe function of a hollow beam 22. In this case, such a knife 8 is expediently of such a narrow construction that, when extended, no large gaps occur in the knife shield 6. This form of construction is particularly useful when a tunnel 5 is being driven through relatively resistant earth.

Claims

1. A method of driving a tunnel around and along a buried main pipe for use in restoring or repairing the main pipe, the main pipe having lateral branch pipes leading thereinto, wherein the tunnel is driven using an open-bottomed knife shield, the knife shield having a plurality of elongate knives arranged side-by-side on a supportframe, and wherein, whenever a branch pipe is encountered by the advancing knife shield, the direct connection between that branch pipe and the main pipe is replaced byan indirect connection, the indirectconnection including aconnectorpipewhich passes th rough the knife shield.

2. A method as claimed in claim 1, wherein the connector pipe is movable longitudinally relative to the knife shield, so thatthe knife shield can be advanced beyond an encountered branch pipe with out breaking the indirect connection between that branch pipe and the main pipe.

3. A method as claimed in claim 1 or Claim 2, wherein the knives of the knife shield are advanced by means of double-acting rams which act between the supportframe and an abutmentframe positioned behind the supportframe.

4. A method as claimed in any one of claims 1 to 3, wherein the knives are provided with rearwardly extending tail extensions, and wherein roof support means are fitted in the shield tail hood formed by said tail extensions.

5. A method as claimed in claim 4when appendant to claim 3, wherein the roof support means is constituted by longitudinally-spaced arches and sup port plates, and wherein the support plates are driven in between the arches and the surrounding earth by retracting the abutment frame.

6. Atunnelling method substantially as hereinbefore described with reference to the accompanying drawings.

7. A knife shield for driving a tunnel around and along a buried main pipe for use in restoring or repairing the main pipe, the main pipe having lateral branch pipes leading thereinto, the knife shield having a plurality of elongate knives arranged side-by-side on a supportframe, and the knife shield being openbottomed, wherein the knife shield is provided with a connector pipe which can be used as part of an indirect connection between a branch pipe and the main pipe, the connector pipe passing through the knife shield, and being movable longitudinally relative to the knife shield, so thatthe knife shield can be advanced relativeto the connector pipe without breaking the indirect connection between a branch pipe and the main pipe.

8. A knife shield as claimed in claim 7,further comprising an abutment frame positioned behind the supportframe,the abutment frame being connected to the supportframe by means of double-acting rams.

9. A knife shield as claimed in claim 7 or claim 8, wherein the knives ofthe knife shield are hollow, and wherein the connectorpipe is displaceably arranged within one ofthe knives.

10. A knife shield as claimed in claim 9, wherein the connector pipe is arranged within one of the bottom (floor-contacting) knives ofthe knife shield.

11. Apparatus as claimed in claim 9 or claim 10, wherein the connector pipe is constituted by a hollow beam.

12. Apparatus as claimed in any one of claims 9 to 11, wherein the outwardly-facing surface of said one knife is provided with a longitudinal slot.

13. A knife shield as claimed in any one of claims 9 to 12, wherein the connector pipe extends substantiallythe entire length of said one knife.

14. A knife shield as claimed in any one of claims 9 to 13, wherein the connector pipe is provided with first and second connection portions at opposite ends thereof.

15. A knife shield as claimed in claim 14, further comprising additional pipes for connecting the first connection portionoftheconnectorpipetothe main pipe, and for connecting the second connection portion of the connector pipe to a branch pipe.

16. A knife shield as claimed in eitherofclaims 14 and 15when appendanttoclaim 12, wherein the second connection portion extends outwardly, and is aligned with the longitudinal slot in said one knife.

17. A knife shield as claimed in any one of claims 7 to 16, wherein the major portion ofthe connector pipe is off-set backfrom the outer surface of the knife shield so that, when the connector pipe is moved to the rear ofthe knife shield, the connector pipe is spaced from the wall ofthetunnel by a distance which is sufficient to permitthe erection of arcuate roof support means to the rear of the knife shield.

18. A knife shield as claimed in claim 17 when appendantto claim 11, wherein the rear end portion of the hollow beam constitutes a widened guide head, the guide head being sized to make sliding contact with the interior of said one knife, and the remaining portion of the beam constituting said off-set portion.

19. A knife shield as claimed in claim 18 when appendanttoclaim 14,wherein the second connection portion is arranged within the guide head.

20. A knife shield as claimed in any one of claims 9 to 19, wherein the connector pipe is provided with a retaining memberwhich can be used to fix the connector pipe within the tunnel.

21. A knife shield as claimed in claim 20,wherein an anchoring ring constitutes the retaining member.

22. A knife shield as claimed in any one of claims 9 to 21, wherein the connector pipe is provided with meansfordetachablyfixing the connector pipe to said one knife.

23. A knife shield as claimed in any one of claims 9 to 22, wherein said one knife is provided with a plurality of apertures which open up into the interior of the knife shield.

24. A knife shield as claimed in any one of claims 9 to 23, wherein the front end ofthe connector pipe is formed with an inclined edgefordeflecting earth present in said one knife into the interior ofthe knife shield.

25. A knife shield as claimed in any one of claims 9 to 24, wherein the front end ofthe connector pipe is provided with a rotatable sharp edge for cleaning the internal walls of said one knife.

26. A knife shield as claimed in any one of claims 7 to 25, wherein the support frame ofthe knife shield is displaceably supported at both bottom side edges on a respective bottom knife, and wherein each bottom knife accommodates a connector pipe, each connector pipe passing through the knife shield and being movable longitudinally relative to the knife shield.

27. A knife shield as claimed in claim 26, wherein each connector pipe is as claimed in any one of claims 9 to 25.

28. Apparatus as claimed in any one of claims 7 to 27, wherein the or each connector pipe constitutes one ofthe knives of the knife shield.

29. A knife shield for driving a tunnel around and along a buried main pipe, the knife shield being substantially as hereinbefore described with referenceto, and as illustrated by, the accompanying drawings.