GB2373830A

GB2373830A - Method of repairing a prestressed concrete pipe

Info

Publication number: GB2373830A
Application number: GB0107992A
Authority: GB
Inventors: John Rees-Stoner
Original assignee: Price Brothers and Co Ltd
Current assignee: Price Brothers and Co Ltd
Priority date: 2001-03-30
Filing date: 2001-03-30
Publication date: 2002-10-02
Anticipated expiration: 2021-03-30
Also published as: GB0107992D0; GB2373830B

Abstract

A method of repairing a prestressed concrete pipe (10,11), includes the steps of inserting into the pipe (10,11) at a location requiring repair annular steel components (15) such that central longitudinal axes of the components (15) are co-axial with a central longitudinal axis of the pipe (10,11) and forming on inner surfaces of the component (15) so as to bridge any gap therebetween and between the said inner surfaces and an adjacent inner surface of the pipe a liquid resistant membrane (19) thereby to prevent egress of liquid from inside of the pipe (10,11) through any such gap. The membrane may be formed by spraying a plastics composition such as polyurethane.

Description

A METHOD OF REPAIRING A PRESTRESSED CONCRETE PIPE This invention relates to a method of repairing a prestressed concrete pipe and to a pipe repaired by the method.

Although prestressed concrete pipes have a reputation for longevity and trouble free service, when problems do occur they are commonly associated with failure of prestress due either to mechanical damage to the prestressing wire or, more usually, to corrosion of the prestressing wire.

Various methods of repairing prestressed concrete pipes have been tried or proposed. These have included replacing corroded sections of pipe with new sections, which is expensive and does not utilise existing work; utilising external steel bands, which requires complete excavation and is not suitable for long lengths; utilising external circumferential post-tensioning tendons, which requires extensive excavation but may be suitable in limited circumstances; utilising welded steel liners which, effectively, create a new pipeline within a pipeline, which is very slow and could result in repairs to long pipelines taking many years to complete; providing internal lining with Kevlar or glass reinforced plastics, which is expensive and slow; and providing internal lining with high strength spray applied elastomer, which is expensive and could result in rupture of the existing pipe due to the elastic deformation needed to mobilise the design stress in the elastomer.

According to the present invention, there is provided a method of repairing a prestressed concrete pipe including the steps of inserting into the pipe at a location requiring repair annular components formed of metal such that central longitudinal axes of the components are co-axial with a central longitudinal axis of the pipe and forming on inner surfaces of the components so as to bridge any gap therebetween a liquid resistant membrane thereby to prevent egress of liquid from inside of the pipe through any such gap.

The invention is based on the observation that in a rectilinear cylindrical pipe the stresses in the pipe wall under static and hydrodynamic loading are essentially hoop stresses.

Longitudinal stresses are effectively zero. This is also true at shallow vertical and horizontal curves where external ground support absorbs eccentric thrusts, the longitudinal components of internal pressure. Thus, an internal steel cylinder repair system in a rectilinear pipeline the effectiveness of the system would depend only on the hoop strength of the cylinder.

However, a major constraint with any repair system is the time required to install it. The transport of long lengths of prefabricated steel pipe inside an existing pipeline is slow and difficult.

In the invention, however, this problem is overcome by installing prefabricated annular components at the repair location.

In operation, the annular components are located at the repair location of a pipe with their central longitudinal axes co-axial with the central longitudinal axis of the pipe and with the components fitting closely one with another (although not necessarily touching one another). A plastics composition is then sprayed onto the internal surfaces of the components and adjacent inner wall surfaces of the pipe to provide a waterproof internal membrane.

The main properties of the membrane are that it should bond well to the steel and to the internal wall surfaces of the pipe; that it should be pinhole free; that it should be sufficiently elastic to cope with any expansions and contractions of the system including opening of the segmental joint gaps under internal pressure due to Poisson's ratio effects; that it should have the mechanical properties needed to span the gap between joints; that it should be compatible with potable water (for water mains); and that it should have a long life expectancy.

A suitable material for providing a membrane is a high build polyurethane. Theoretical analysis and testing have defined the membrane thicknesses necessary to provide an effective barrier against leakage when covering various separations between annular components at specific pressures.

Aspects of the invention will now be described, by way of example only and with reference to the accompanying drawings :

Figure 1 is a diagrammatic cross section of a prestressed concrete pipe repair carried out in accordance with one embodiment of the method in accordance with the present invention, Figure 2 is a diagrammatic cross section of a prestressed concrete pipe repair carried out in accordance with another embodiment of the method in accordance with the present invention, Figure 3 is a diagrammatic representation of a method of installing an annular component in a pipe in carrying out another embodiment of the method in accordance with the present invention, Figure 4 is a perspective view of a saddle and tube for use in a manhole of a pipe when repaired by the method in accordance with the present invention, Figure 5 is a cross section of a manhole of a pipe when repaired by the method in accordance with the present invention, and Figure 6 is a diagrammatic representation of the repair method in accordance with the present invention, applied to pipes which have been installed with a deflection of up to 35 mm at the joint.

Referring now to Figure 1 of the drawings, there is shown a diagrammatic cross section of two adjoining portions 10 and 11 of prestressed concrete pipe which are united one to

another by a circumferential steel joint ring 12. The joined portions 10, 11 are shown as having been repaired by a first embodiment of the method in accordance with the present invention. A circumferential portion of a lining 13 of the pipe is cut adjacent a location where the portions 10,11 are joined to provide a circumferential recess 14 which extends inwardly from the interior of the pipe as far as the joint ring 12. A series of annular steel components 15 are then located within the pipe so that central longitudinal axes of the annular components 15 are coaxial with a central longitudinal axis of the pipe and the annular components 15 are spaced axially one from another by a distance of approximately 3.5 mm, the annular components 15 lining the failed area of the pipe and an end annular component 15 being located adjacent the location where the portions are joined. The gap between an outer circumference of the annular components 15 and an adjacent inner circumference of the lining 13 is filled with a gunite filler 16. The recess 14 has located therein a radial, circumferential plate 17 which is united with an adjacent annular component 15 and with the joint ring 12 by continuous welds 18. The exposed inner surfaces of the annular components 15, the plate 17 and the joint ring 12 are then sprayed with a polyurethane composition which sets to provide a continuous watertight membrane 19. The recess 14 is then made good with a mortar filler 20.

The plate 17 may be dispensed with, as shown in Figure 2. In such circumstances, the bond between the membrane 19 and the joint ring 12 is relied upon to prevent leakage.

The examples shown in Figures 1 and 2 generally refer to a large pipes having diameters in the range of 2, 000 mm to 4,000 mm, which can be accessed by working inside the pipes.

For small pipes having diameters in the range of 1,000 mm to 2,000 mm, which provide for less manoeuvrability, annular components are formed in two halve steel segments 21 and 22, as shown in Figure 3. The end portions of each of the segments 21,22 have steel lugs 23,24 welded on opposite sides, each of the lugs having a stepped peripheral edge 25.

The two segments 21,22 are secured together by clips 26 formed of metal each having an internal cavity 27 which is undercut, as shown at 28. The clips 26 are slid onto the lugs 23 and 24 to join together segments 21 and 22.

The void between the segments 21,22 and the existing pipewall 29 is filled with a gunite filler 30. An inner surface of the annular component 21,22 and an adjacent surface of the inner wall 29 of the pipe are then sprayed with a polyurethane composition to provide a membrane 31.

A manhole located in pipes to be repaired by the method in accordance with the present invention are underlined by a steel saddle 32 having a radially extending tube 33, as shown in Figure 4, for extending into an existing outlet of the pipe.

The saddles 32 would be installed into a pipe before installation of the annular components, one of which is shown at 34 in Figure 5. The tube 33 extends through the saddle 32 and the tube 33, the saddle 32 and the annular component 34 are welded together and a polyurethane composition is sprayed on the inner surfaces to provide a membrane 35. Pipes which are defective on either side of a deflected joint can be repaired by the method in accordance with the present invention using segments with a varying joint gap to facilitate a transition through the deflected joint.

Claims

1. A method of repairing a prestressed concrete pipe including the steps of inserting into the pipe at a location requiring repair annular components formed of metal such that central longitudinal axes of the components are co-axial with a central longitudinal axis of the pipe and forming on inner surfaces of the components so as to bridge any gap therebetween a liquid resistant membrane thereby to prevent egress of liquid from inside of the pipe through any such gap.

2. A method as claimed in Claim 1 wherein the components are formed in separate parts which are united one with another to form the components.

3. A method as claimed in Claim 2 wherein the parts are united one with another by metal clip means.

4. A method as claimed in any one of the preceding claims wherein the membrane is formed by spraying a plastics composition.

5. A method as claimed in Claim 4 when the plastics composition is polyurethane.

6. A prestressed concrete pipe repaired in accordance with the method as claimed in any one of the preceding claims.

7. A method of repairing a prestressed concrete pipe substantially as hereinbefore described and as illustrated in Figure 1 or Figure 2, Figure 3 or Figures 4 and 5 of the accompanying drawings.