GB2123918A - Plastics pipe liner - Google Patents

Abstract

A liner 12 for a conduit 10 of concrete or other rigid material comprises a tube of plastics material having a layer of granular material such as sand bonded to its outer surface. The liner 12 is self-supporting and flexible relative to the rigid conduit 10. In use the liner 12 is inserted into the conduit, and the space 5 between the two is filled with a grouting material such as cement which forms an intimate bond with the granular material on the outside of the liner. <IMAGE>

Description

SPECIFICATION Conduit liner and method of lining conduit This invention relates to conduit liners and, in particular, to a liner for a large bore conduit, viz having an internal diameter of 300 mm or greater, which conduit is constructed from a material such as concrete or other rigid material.

It is known to provide a large bore conduit of concrete or clay with an inner conduit of plastics material such as PVC, such that if the outer conduit is damaged the inner conduit will prevent leakage of the material being conveyed therein. These known plastics "liner" conduits are rigid and are strong enough to withstand pressure in their own right. Accordingly, the walls of such "liner" conduits are considerably thick (25 mm or greater) to provide the necessary strength to withstand pressure. Large amounts of plastics material are used in the manufacture of such "liner" conduits which is consequently costly and, therefore, generally uneconomical. The known large bore "liner" conduits are also difficult to install because they lack flexibility.

U.S. Patent No. 3,210,095 describes a flexible, thin-walled (circa 2.5 mm) thermoplastics liner for a steel conduit having an internal diameter of about 25 mm. The thermoplastics liner is capable of radial expansion within the steel conduit and to be supported by said steel conduit when there is a build-up of pressure within said liner. It is stated in U.S. Patent Specification No. 3,210,095 that a substantially smooth, continuous inner surface must be provided in the conduit which encases the thermoplastics liner, because the internal pressure will cause the thermoplastics material to extrude through a relatively small opening as a result of the cold flow characteristics of mostthermoplastics materials.

It has also been proposed to provide the inner surface of a concrete conduit with a lining of a plastics material which is bonded thereto. However, such conduit linings have not been successful in practice due to the difficulty of bonding plastics materials to concrete, since concrete forms a dust which prevents bonding of plastics material thereto, particularly where heat is involved in the application of the plastics material.

U.S. Patent Specification No. 3,381,718 describes a plastics liner for a concrete pipe which liner comprises two or more plies of a plastics sheet material, such as polyvinyl chloride, securely bonded together and bonded to a ply of backing material which displays the property of being susceptible to very secure bonding to concrete by a bonding agent such as an epoxy adhesive, so as to bond the vinyl plastics material intimately to the concrete. Suitable materials for the backing layer are stated to be cotton fabrics and fabrics of glass. The adhesive bonding agent must be comprised of 100% solid material with no volatile matter or solvent that can be trapped between the liner and the concrete surface. Accordingly, it may be necessary to evaporate off solvent materials from the bonding agent when carrying out the method described in U.S.

Patent Specification No. 3,381,718. During the bonding step heat must be applied to maintain a suitable curing temperature for the bonding agent which is necessary to effect a thorough bonding of the lining to the concrete pipe. Furthermore, the surface of the concrete pipe to be lined must first be cleaned and freed of loosely adhering materials, such as by sandblasting the interior surface of the concrete pipe.

It has also been proposed to bond a PVC line directly to a concrete conduit by providing hair-like fibres or filaments of plastics material on the bonding surface of the liner in an attempt to overcome the problems involved in bonding a plastics material directly to concrete. However, such liners are not practical for use in civil engineering applications.

Three main problems are experienced with large-bore, low pressure conduits, for example conduits which are used as part of a sewage system. Firstly, the conduits may leak from the inside out due to the pressure of fluids being conveyed. Secondly, the conduits tend to leak from the outside in due to pressure from ground water. Thirdly, the conduits frequently require to be lined either to reinforce the structure of the conduit or to repair the conduit because the conduit is in a state of collapse. As will be apparent from the discussion of the prior art above, there is currently no satisfactory method of lining a concrete pipe which may be used in normal wet civil engineering procedures.

It is an object of the present invention to provide a liner for a larger bore conduit of concrete or like rigid material, which liner can be readily inserted gn the conduit and which can be cold-bonded in situ to the concrete conduit under normal wet civil engineering procedures.

Accordingly, the invention provides a liner for a conduit of concrete or other rigid material, the liner comprising a tube of plastics material having a layer of granular material bonded to its outer surface, the liner further being self-supporting and flexible relative to the rigid material of the conduit.

The invention further provides a method of lining a conduit of concrete or other rigid material, comprising inserting in the conduit a liner as defined above, the liner being a loose fit within the conduit, and filling the space between the liner and the conduit with a grouting material which forms an intimate bond with the layer of granular material on the outer surface of the liner.

Preferably, the liner is made of a thermoplastics material. Suitable thermoplastics materials are low density polyethylene, high density polyethylene, nylon and polycarbonate, the particular material chosen depending upon the particular properties required of the liner. If desired a laminate of different material may be used to give specific properties.

The liner material may be chosen so as to protect the concrete or other rigid material and the grouting material from the damaging or corrosive effects of the particular material being conveyed by the conduit.

Alternatively, the liner material may be chosen so as to protect a fluid being conveyed in the liner from the concrete or other rigid material of which the conduit is made or to protect said fluid from environmental effects.

Examples of suitable liner materials for particular applications are as follows: Material Properties Low density polyethylene Reduction of friction.

Protection from contamination.

Low chemical loading.

Protection against leaks.

High density polyethylene General chemical resistance.

Average temperature 20 C.

Glass or carbon fibre Increased rigidity.

reinforced high density Low creep.

polyethylene or other thermoplastics material Polycarbonate Temperatures up to 100 C.

Nylon Pressure conditions.

Medium temperatures (up to 60 C).

Specific chemical resistance.

The liner may also be constructed in the form of an integrally moulded sandwich structure, for example of polyethylene. Such a sandwich structure is suitably composed of an inner and an outer solid skin of thermoplastics material spaced apart by an intermediate layer of foamed thermoplastics material. A liner having a sandwich structure has increased rigidity and furthermore the sandwich structure will act as a good insulating material which is desirable in certain applications of the liner according to the invention.

The liner will generally have a wall thickness in the range 2-12 mm since for most applications it is desirable that the wall thickness of the liner be as thin as possible.

The liner according to the invention is particularly suited for use with large bore conduits, such as conduits having a diameter in the range 300-2,000 mm or greater.

The shape of the liner will largely be determined by the shape of the outer conduit. For this reason, the liner will normally have a circular or elliptical cross-section.

The surface configuration of the wall of the tube is determined by the particular physical property, via mechanical/hydraulic, required of the liner.

Some suitable surface configurations for particular applications are as follows: Surface configuration Physical properties required Smooth Improved flow.

Chemical resistance.

Square circumferential Increased rigidity.

corrugations Rounded circumferential Increased flexibility.

corrugations External circumferential Increased rigidity.

ribs In all cases the tube of plastics material may be reinforced for inreased rigidity by winding a steel wire helically around the outer surface of the tube, or by placing a steel net around the outer surface of the tube.

Nevertheless it is important that the tube is not made so rigid that it cannot be manipulated within the conduit, for example to negotiate gentle bends or minor irregulaties resulting from cracking and relative movement of adjacent parts of the conduit. Thus the liner should have at least a limited degree of flexibility relative to the concrete conduit, and this also permits the liner to withstand a certain degree of movement of the conduit subsequent to its installation. On the other hand, the liner should not be so flexible that it is not self-supporting, since this would also povide difficulty in inserting the liner into the conduit due to its tendency to collapse.

If a smooth-walled liner is employed, it will normally be necessary to provide additional internal support within the tubular liner to support the additional weight when the generally annular space between the conduit and the liner is being filled with grouting material, this internal support being removed when the grouting material has hardened. Examples of suitable additional internal support are discussed below.

In the case of a corrugated liner, a liner having a sandwich structure, or a liner which is reinforced by the incorporation of glass or carbon fibres in the body of the plastics material, additional internal support is not normally necessry during the grouting step, since such liners have sufficient inherent rigidity to prevent inward collapsing or sagging of the liner due to the pressure of the grouting material before it hardens.

The conduit provides the necessary support against a built-up of internal pressure caused by the transit of material within the liner. The conduit also protects the liner against external mechanical damage. If necessary the walls of the tube may be thickened, that is to a thickness greater than 12 mm, to reduce stress in the material of the liner where the liner is used for high pressure applications or where external ground water might cause collapse. However, ordinarily a wall thickness of 6 mm will suffice under normal operating conditions of the liner.

Where the conduit is particularly liable to be damaged due to subsidence or similar displacement of surrounding ground with consequent weakening or rupturing of the bond between the liner and the grouting material and deformation of the joints of the liner, the abovementioned flexible corrugated lining will prevent leakage despite such damage, dependent on the limits of displacement of the particular type of corrugation selected for the wall of the liner.

In the case of a liner having circumferential corrugations or circumferential external ribs about its periphery, these may be graded so that in situ the corrugations or ribs at the top of the liner have a greater depth than the corrugations or ribs at the bottom of the liner so as to prevent sagging of the liner during installation. The flow resistance of corrugated liners may be decreased by providing a smooth further liner within the main corrugated liner.

The grouting material is preferably cement, and the granular material is preferably sand having an average particle size in the range 1-3 mm. The sand, which is intimately bonded to the liner material such as by fusion, provides a roughened surface which allows the cement grouting material to be cold bonded to the liner and thereby overcome the normal problem of adhesion between cement and a plastics material, which is generally difficult or impossible to achieve due to the smooth surface of the plastics material.

The grouting material also spreads into and fills any cracks in the conduit in addition to occupying the annular space between the conduit and the liner.

The present invention has particular application in the repair of old brick built sewers wherein the mortar between the bricks has deteriorated and the sewer is in a weakened state. The pumping of grouting material into the generally annular space between the liner and the bricks defining the walls of the sewer also fills up any spaces or voids between the bricks and thereby strengthens the entire structure.

The grouting material also obviates the build-up of pressure which would normally occur in the annular space in a damaged conduit due to leakage therein of ground water.

The liner may be formed by conventional moulding or fabrication techniques. For example, the liner may be moulded using a mould and a suitable rotational moulding machine such as by moulding in a full rotation or 'Rock and Roll' machine or other similar moulding machine. Suitable fabrication techniques involve the production of the liner from a sheet of plastics material in conventional manner. The liner may also be formed by a suitable plastics-forming process. The length of liner which may be formed is limited only by the available machine size.

Where the liner comprises one of a number of individual lengths or sections which are joined end-to-end to form the complete conduit lining, the liners are normally 2 mm long and are preferably joined together in situ. Such lengths of liner may be welded together circumferentially without significant loss of physical properties.

The individual lengths of liner may have integrally moulded at their opposite ends the complementary elements of a joint. The joints may be welded or sealed depending on the conditions of use so as to prevent leakage at the joint. For example, a flexible Mastic sealer may be used for sealing purposes.

However, if welding of the joint is not possible, for example because of the presence of a lot of water such as would be encountered in a damaged sewer, a conventional self-sealing joint may be used.

Typical types of joints which may be employed with the liner according to the invention include a socket and spigot joint which is sealed by welding or a self-sealing socket and spigot joint when such is required. A rubber ring joint may also be used. Furthermore, butt welding may be used to join the lengths of liner together under certain conditions.

A number of techniques may be used to bond the granular material to the liner.

For example, when sand is the granular material used, the sand may be heated on a hot plate and then the formed liner rolled on the hot plate causing the liner to soften and the sand to fuse thereto.

Alternatively, the formed liner may be blasted with hot sand using an airless sand blasting technique. If an airless system is not used cooling of the sand would occur. Another technique is to use an electrostatic charge to deposit the sand on the heated surface of the liner.

During application of hot sand, wetting of the individual sand particles occurs due to changes in the surface tension of the plastics material caused by heating. Accordingly, the grain size of the sand particles is important if they are not to become absorbed into the surface of the plastics liner. In practice it has been found that an average grain or particle size of 1-2 mm is suitable to achieve the desired roughened texture of the surface of the liner. Furthermore, it is desirable to have a coverage of sand on the liner of 40-60 grains/cm2.

Manholes, fittings and non-integral joints can be constructed from the same material as the liner to provide continuity of protection.

Preferably, to insert the liner in a conduit a 'pulling-in' flange, which is integral with the wall of the liner, is used in association with a 'pulling-in' ring, which ring is clamped to the flange. The 'pulling-in' ring is secured to a winch rope and the liner drawn through the conduit into the required position by means of a winch. After installation and hardening of the grouting material the flange is cut off. The flange provides additional support internally of the liner during the filling of the annular space between the conduit and the liner with grouting material.

When a number of discrete liners are used, the individual lengths are pulled through the conduit in sequence and joined together in situ. When a given length of liner is in position and the grouting material has been inserted therearound and has hardened, the 'pulling-in' flange is cut off and the joint between adjacent sections of liner is welded, if welding is required.

A suitable electrical circuit, such as an earthed strip of aluminium foil, is preferably incorporated at each joint to ensure that the joint is leak free after installation of the liner. Such a circuit also enables tests to be carried out during the life of the liner to confirm continued leak-free functioning of the liner. Where the conduit is used as a secondary protection from leaks, such a circuit provides a 'fail-safe' warning system due to completion of the circuit by a leaking material. The joints are tested by means of a standard spark tester.

The invention will be understood from the following description of embodiments thereof given by way of example only with reference to the accompanying drawings in which :- Figure 1 is a front elevation in section of portion of a conduit employing a liner according to the invention; Figure 2 is a front elevation in section of another liner according to the invention; Figure 3 is a front elevation in section of a further liner according to the invention, employing a self-sealing joint; Figure 4 is a schematic representation of a section through a conduit employing a liner according to the invention; and Figures 5 and 6 illustrate the formation of a joint between a liner according to the invention and a side entry pipe.

Referring to Figure 1 of the drawings there is indicated portion of a reinforced concrete pipe 10 having positioned therein a lining 11 of the relatively flexible, high density polyethylene material. The pipe 10 has a nominal diameter of 1500 mm. The lining 11 is made up of a number of discrete liners 12. Portions of two such liners 12a and 12b are shown in Figure 1. The lining 11 is spaced apart from the inner surface 13 of the pipe 10 by a generally annular space S approximately 10 mm wide.

In practice, the actual diameter of the concrete pipe may well deviate from the nominal diameter and allowance must be made for any such deviation when selecting the liners so that they will always be a loose fit and self-supporting in the pipe 10 during installation.

End 14 of the liner 12afits into an enlarged end 15 ofthe liner 126 thereby forming a conventional socket and spigot joint. Grouting cement (not shown) is pumped in the annular space S and is allowed to harden whereupon the liners 12a and 12b are welded together by a spot welding indicated at 16, after a flange 17 (shown in dotted outline) which serves as a 'pulling-in' flange and internal support or stiffening during grouting has been cut off. A test strip of aluminium foil 18 is positioned intermediate the overlapping ends 14 and 15 of the liners 12a and 12b and is connected to a copper wire 19 by means of which it is earthed. A conventional spark tester is used to test that the weld is continuous.Prior to forming the joint between the ends 14 and 15, the foil 18, which is attached to one of the ends 14 or 15, is tested by means of the spark tester to ensure that the strip of aluminium foil 18 is intact. The aluminium foil 18 also allows one to check for leaks during periodic servicing of the lining 11 and the pipe 10. Accordingly, leaks may be detected without excavating the pipeline. The concrete pipe 10 and the lining 11 form part of a sewer.

The thickness tofthe liners 12 is such that they are impermeable to liquids conveyed by the lining 11 and so that they are sufficiently rigid to be self-supporting during installation and, together with the additional support provided by the 'pulling-in' flange 17, during grouting. The liners 12 are supported by the pipe 10 and the layer of grouting cement when there is an increase an internal pressure in the lining 11. However, a large bore pipe of the type depicted in Figure 1 is not normally'run full' except during flooding or other exceptional conditions.

Pipe 10, in addition to providing pressure support, also prevents mechanical damage to the liners 12. The liners 12 in turn protect the pipe 10 from attack by corrosive materials, the chemical composition of the liners being chosen for its high resistance to chemicals and its resistance to 'stress cracking' due, for example, to the presence of detergents in the lining 11.

The liners 12 have bonded to their external surface a layer of sand (not shown) which provides a roughened surface which permits strong adhesion of the liners 12 to the layer of grouting cement (see Figure 4).

Referring to Figure 2 of the drawings, there is illustrated a portion of a lining 11' for an outer conduit of rigid material (not shown) which has a nominal diameter of 1500 mm. The lining 11' is composed of high density polyethylene material and is made up of a plurality of discrete liners 12'. Portions of two such liners 12a' and 1 2b' are shown in Figure 2. The lining 11' is used for conveying effluent which may contain a wide variety of chemical materials. In situ, the individual liners 12' of the lining 11' are spaced apart from the conduit so that they are a loose fit therein during installation and provide a generally annular space between the conduit and the lining 11' for filling with a grouting material.

End 14' of the liner 12a', which has an integral 'pulling-in' flange 17', fits into end 15' of the liner 126'. the 'pulling-in' flange 17' has a 'pulling-in' ring 20 clamped thereto. In use, the 'pulling-in' ring 20 is secured to a winch (not shown) so that the liner 12a' is pulled through the conduit into contact with the liner 1 2b' whereupon the two liners are joined together in situ. The joint indicated at 21 is rendered leak proof by welding circumferentially at a point indicated by 16' when the flange 17' is cut off, optionally after the grouting material has hardened, and the ring 20 is removed for re-use. Walls 22 (which are 2.5 mm in thickness) of the liners 12' have circumferential corrugations.The corrugations increase the rigidity of the lining 11' as compared with the smooth walls of the lining 11 of Figure 1. Furthermore, the corrugations are graded about the periphery of the liners 12' so that in situ the depth of the corrugations 23 (25 mm) at the top of the lining 11' is greater than the depth of the corrugations 24 (10 mm) at the bottom of the lining 11'. This graded corrugation prevents sagging of the top part of the liners 12' in situ during installation and filling of the annular space with grouting material.

The use of corrugated liners as depicted in Figure 2 results in a very strong bond between the grouting cement and the liners due to interlocking of the corrugations and the grouting cement.

Referring to Figure3 ofthe drawings, there is indicated portion of a concrete pipeline 10"forming partofa sewer and having positioned therein a lining 11" of a relatively flexible, high density polyethylene material.

The lining 11" is made up of a number of discrete liners 12" each 2 m in length. Portions of two such liners 12a" and 12b" are shown. The lining 11" is spaced apart from the inner surface 13" of the pipeline 10" by a generally annular space space S". Liners 12a" and 12b" have integrally moulded at their respective ends 14" and 15"the complementary elements 25 and 26 of a conventional self-sealing joint. Grouting cement (not shown) is pumped into the annular space S" and is allowed to harden. Some grouting cement may enter into recesses 27 defined between elements 25 and 26 of the joint.

The use of integrally formed or moulded joints is preferable to using separate joint components since one has no loose elements and furthermore one has continuity of protection and flow characteristics. End 15" also has integrally moulded thereto a 'pulling-in' flange 20" which in addition to enabling the liner 1 2b" to be pulled through the pipeline 10" provides additional internal support and stiffness of the lining 11" during pumping in and hardening of the grouting cement. When the grouting cement is hardened the 'pulling-in' flange 20" is removed.

Referring to Figure 4 of the drawings, there is illustrated a scaled-up portion of a liner 12 as depicted in Figure 1 bonded to a layer of grouting cement 28 which fills the annular space S between the pipe 10 and said liner 12. The plastics liner 12 has bonded to its outer surface 29 a layer of sand 30 which provides a roughened surface which readily adheres to the grouting cement 28 and enables an intimate bond to be achieved between the liner 12 and the grouting cement 28.

It will be appreciated that the section depicted in Figure 4 applies equally to the liner/conduit combinations depicted in Figure 2 and 3.

A technique for forming a joint between a liner according to the invention and a side entry pipe is illustrated in Figures 5 and 6, which are cross-sectional views of a circular concrete conduit 10 containing a plastics liner 12 respectively before and after forming the joint.

The side entry pipe 35 enters the conduit 10 from one side and is cut generally flush with the inside surface of the conduit, Figure 5. The liner 12 is next inserted in the conduit 10, the liner initially being a loose fit as shown. Now, prior to introducing the grouting material into the annular space 5, the material of the liner is locally heated in the region 36 adjacent the cut end of the pipe 35. The heating is such as to soften but not melt the plastics material in the region 36, and a "safe" heat source should be used i.e. one which does not present a bare flame to the interior of the conduit so as to avoid the risk of igniting any flammable gases which might be present. Once softened, the material in the region 36 is subjected to outward pressure sufficient to rupture the plastics material, the ruptured edges 37, Figure 6, forming a joint with the end of the side entry pipe.The outward pressure may be applied mechanically or using compressed air, and both the local heating and subsequent outward pressure may be applied by a robot manipulator inserted in the liner 12.

Finally, the cement grouting (not shown) is pumped in the space S. The grouting will complete the seal between the ruptured edges 37 and the pipe 35 by entering any small spaces between the two.

In order to locate the liner 12 in position in the conduit 10 prior to forming the joint between the side entry pipe 35 and the liner, a number of blisters 38 may be formed in the surface of the liner 12 generally opposite the location of the side entry pipe 35. These are formed in the same way as for the joint described above, except that the outward pressure used is not sufficient to rupture the plastics material.

If desired, circumferentially spaced blisters 38 may be provided around the liner 12 at any position where it is required to provide positive location of the liner, and it is not necessary that these blisters are located only in regions of the liner that a side entry joint is required.

It will be appreciated that the liner according to the invention overcomes the three main problems associated with large-bore, low pressure conduits recited above. Firstly, the liner withstands internal pressure since it is constrained by the conduit. Secondly, the liner withstands external pressure since it is bonded to the conduit. Thirdly, the liner acts as a type of shuttering for the cement grouting of a defective or damaged conduit. A further advantage is that as the liner is reinforced by the cement grouting which is itself bonded to the conduit, it acts as a composite with the main structure of the conduit.

The liner according to the invention is particularly advantageous since it can be installed under normal wet engineering procedures. The installation procedure does not require application of heat or special dry or clean conditions. A defective or damaged conduit such as a sewer is impossible to clean or dry out. The liner according to the invention can be installed even when water is leaking inwards from defective conduit walls.

Furthermore, the liner is compatible with the grouting cement and becomes solidly bonded via the cement to the conduit structure so as to prevent pressure build-up between the liner and the conduit.

The use of a liner according to the invention results in a decrease in friction in a pipeline. The liner is robust and not easily damaged and is economical and easy to install.

Claims (19)

1. A liner for a conduit of concrete or other rigid material, the liner comprising a tube of plastics material having a layer of granular material bonded to its outer surface, the liner further being self-supporting and flexible relative to the rigid material of the conduit.

2. A liner as claimed in claim 1,wherein the granular material is sand.

3. A liner as claimed in claim 1, or 2, wherein the tube has circumferential corrugations.

4. A liner as claimed in claim 1 or 2, wherein the tube has external circumferential ribs.

5. A liner as claimed in claim 3 or 4, wherein the corrugations or ribs are deeper on one side of the tube than the other.

6. A liner as claimed in any preceding claim, wherein the plastics tube is reinforced.

7. A liner as claimed in claim 6, wherein the reinforcement comprises a helical wire around the outer surface of the tube.

8. A liner as claimed in claim 6, wherein the reinforcement comprises a metal net around the outer surface of the tube.

9. A liner as claimed in claim 6, wherein the reinforcement comprises glass or carbon fibres incorporated in the body of the plastics material.

10. A liner as claimed in any one of claims 1 to 4, wherein the tube comprises inner and outer layers of solid plastics material and an intermediate layer of foamed plastics material.

11. A liner as claimed in any preceding claim, wherein the opposite ends ofth liner are formed with the complementary elements of a joint.

12. A method of lining a conduit of concrete or other rigid material, comprising inserting in the conduit a liner as claimed in any preceding claim, the liner being a loose fit within the conduit, and filling the space between the liner and the conduit with a grouting material which forms an intimate bond with the layer of granular material on the outer surface of the liner.

13. A method as claimed in claim 12, wherein prior to the introduction of the grouting material the liner is located in the conduit by a plurality of outwardly extending blisters in the surface of the plastics tube, each blister being formed in situ by locally heating the liner to soften the plastics material and then subjecting the softened material to outward pressure insufficient to rupture the material.

14. A method as claimed in claim 12 or 13, further including forming a joint between the liner and a side entry pipe prior to the introduction of the grouting material, the joint being formed in situ by locally heating the liner to soften the plastics material in the region adjacent the end of the side entry pipe and then subjecting the softened material to outward pressure sufficient to rupture the material, the ruptured edges of the plastics material forming a joint with the end of the side entry pipe.

15. A method as claimed in claim 12, 13 or 14, wherein a plurality of liners are interested in the conduit and joined end to end.

16. A method as claimed in claims 12, 13, 14 or 15, wherein the grouting material is cement.

17. A method of lining a conduit substantially as described herein with reference to Figure 1,2,3 or 5 of the accompanying drawings.

18. A conduit lined by the method claimed in any one of claims 12 to 17.

19. A conduit liner substantially as described herein with reference to Figure 1,2 or 3 of the accompanying drawings.