GB2188997A

GB2188997A - Protecting pipe joints

Info

Publication number: GB2188997A
Application number: GB08609041A
Authority: GB
Inventors: C R Smith; J P Doody
Original assignee: FAIRCLOUGH CONSTR GROUP
Current assignee: FAIRCLOUGH CONSTR GROUP
Priority date: 1986-04-14
Filing date: 1986-04-14
Publication date: 1987-10-14
Also published as: GB2188997B; GB8609041D0

Abstract

Pipe ends are joined by a rigid band 5 extending over rebates on the ends of both pipes 1, 2 and one pipe 1 has a secondary rebate adjacent to and shallower than the main rebate bearing a secondary band 12 extending over the end of the primary band 5. The joint may be used for pipe jacking, the secondary band 12 being arranged on the trailing end of the leading pipe 1 to prevent ingress of material to the space between the primary band 5 and the rebates. <IMAGE>

Description

SPECIFICATION Pipe joints This invention relates to joints between adjacent concrete pipe sections laid end-to-end to form a composite pipe and is applicable to pipes installed by the method known as thrust jacking" or "pipe jacking" in which successive concrete pipe sections are forced through the ground by pressure applied to one end of the pipe, each newly added section being used to push forward the preceding pipes.

In practice it is difficult to maintain accurate axial alignment of successive pipe sections and consequently adjacent sections are frequently required to transmit thrust from one to another through a small area of mutual contact. The resulting concentration of load tends to produce cracking and spalling of the pipe ends.

British Patent Specification 1393363 describes an arrangement which seeks to avoid this problem by providing a pipe joint in which one pipe end is externally rebated and the adjacent mating pipe has an externally rebated end portion which end carries a thin-walled, substantially rigid band of material wherein the band is fitted directly on the rebated end portion and projects beyond the end of said mating pipe to form a socket which engages over the external rebate of said one pipe end, and an O-ring seal is received in a space between the band and the said one pipe end.

When the pipe joint described in British Patent Specification 1393363 is used for pipe jacking there is a substantial risk of material from the ground entering the space between the band and the exterior surface of the rebate of the trailing end of the leading pipe and this material can cause substantial damage to, or displacement of, the O-ring seal. Such damage may cause the joint to leak.

The present invention is intended to avoid or alleviate this problem by providing a pipe joint of the above-mentioned type in which the trailing end of the leading pipe is provided with a secondary rebate, adjacent to and of lesser depth than the primary rebate on which the rigid primary band is positioned, and a secondary band is secured to the leading pipe within the secondary rebate and extend rearwardly over at least part of the primary rebate so that the leading edge of the primary band may occupy the space between the primary rebate and the inner surface of the secondary band.

The secondary band may be firmly secured to the secondary rebate of the leading pipe by welded anchors or other known means. The secondary band preferably has an outside surface which is substantially flush with the outside surface of the pipe and may be of steel or any other material having the necessary strength.

When the pipe is installed in the ground by pipe jacking the secondary band, which covers the leading edge of the primary band in the primary rebate, prevents entry of material from the ground into the space between the primary band and the primary rebate.

The primary band generally extends over the rebates on the ends of both pipes to be joined and a seal, generally of resilient material, may be provided between both rebates and the primary band. The abutting ends of the concrete pipes may be separated by a ring of deformable material to provide a further seal between the abutting ends themselves and to assist in distributing thrust.

A pipe joint according to one embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic cross-section of a pipe joint before tightening, Figure 2 is a similar cross-section of the joint after tightening.

The drawings show the ends of a pair of concrete pipes 1 and 2 which are to be joined together when the pipes are installed underground by pipe jacking. When the pipes are installed the leading pipe 1 is forced through the ground in the direction of arrow F by hydraulic pressure applied to its trailing end.

When pipe 1 has advanced by the required distance it is joined to the leading end of pipe 2 and hydraulic pressure is then applied to the trailing end of pipe 2 to continue advance of the composite pipe. A series of pipes are installed end-to-end in this way until the composite pipe formed has advanced by the requisite distance.

The trailing end of each pipe 1 is provided with an external rebate 3 and the leading end of the following pipe 2 has a similar rebate 4.

The rebates are dimensioned to receive a thinwalled rigid band 5, which may be of steel or other material having the requisite strength.

The axial length of band 5 is such that when the joint is tightened as shown in Fig. 2 the band occupies substantially the whole of the rebates 3 and 4.

The rebates of both pipe ends are both provided with an external peripheral groove 6, 7 containing a sealing ring of resilient plastics material 8, 9 which forms a fluid-tight seal between the pipe ends and the band 5 when the pipe ends are joined together. A ring 10 of compressible plastics material is also provided between the trailing end of pipe 1 and the leading end of pipe 2 to act as packing between the pipes.

The trailing end of pipe 1 is also provided with a secondary rebate 11, adjoining and of lesser depth than rebate 3, and a secondary band 12 of steel or other rigid material is positioned in secondary rebate 11. The outer surface of secondary band 12 is substantially flush with the outer surface of pipe 1, the leading end of the second band abuts the leading end of the rebate 11 and the secondary band extends rearwardly beyond the trailing end of rebate 11 so that it overlaps the leading part of rebate 3 to a significant extent.

Secondary band 12 is anchored into the body of pipe 1 by welded anchors or other means ensuring secure attachment to the pipe.

The depth of rebate 3 and band 12 are such that the leading end of band 5 may slide into the space defined by the peripheral surface of rebate 3 and the inner surface of secondary band 12.

When the pipes are installed by jacking the secondary band has already been fitted to the trailing end of pipe 1. In order to join the following pipe to the leading pipe, pipe 2 is arranged as shown in Fig. 1 with band 5 extending over seals 8 and 9 and ring 10 positioned between the pipe ends. When pipe 2 is advanced behind pipe 1 the joint is tightened as shown in Fig. 2, band 5 occupying substantially all the rebates 3 and 4 and seals 8 and 9 and ring 10 providing fluid-tight sealing.

During advance of pipes 1 and 2 by jacking the band 5 keeps the pipe ends aligned and ring 10 assists in distributing the jacking force transmitted from pipe 2 to pipe 1 around the periphery of the joint.

During the jacking operation the secondary band 12, being firmly anchored to pipe 1 and extending rearwardly over the leading end of the band 5, prevents ingress of unwanted material which might otherwise penetrate between band 5 and the outer surface of rebate 3 and damage the joint.

Claims

1. A pipe joint in which one pipe end has an external primary rebate and the adjacent mating pipe has an externally rebated end portion which carries a thin-walled, substantially rigid primary band of material wherein the band fits around the rebated end portion and projects beyond the end of said mated pipe to form a socket which engages over the primary rebate of said one pipe end, said one pipe end being provided with a secondary rebate adjacent to and of lesser depth than the primary rebate and a secondary band fitted on the secondary rebate, the secondary band extending over at least part of the primary rebate so that part of the primary band may occupy the space between the primary rebate and the inner surface of the secondary band.

2. A pipe joint according to claim 1, in which seals of resilient material are provided between the rebates of both pipes and the primary band.

3. A pipe joint according to claim 1 or 2, in which the external surface of said secondary band is substantially flush with the outer surface of said one pipe.

4. A pipe joint according to any preceding claim, in which the abutting pipe ends are separated by a seal of deformable material.

5. A pipe joint, substantially as hereinbefore described with reference to the accompanying drawings.

6. A method of pipe jacking, in which pipes joined by a joint according to any preceding claim are advanced through the ground by force applied to the trailing pipe, the trailing end of the leading pipe being provided with said secondary rebate and said secondary band.