Patch, line or dig

What happens before any remedy is chosenPreparation

Nothing is lined, patched or dug until the run has been cleaned and looked at again. The sequence is fixed, and the remedy is chosen at the end of it rather than at the start.

1. 1 Clean the bore out Jet and cut

   Deposits are jetted out, scale is cut back and roots are cut to the pipe wall, so what is left is the pipe rather than what was sitting in it.

2. 2 Survey it again Second log

   A grade 4 obstruction that jets away was a grade 2 service defect wearing a disguise, and only the second survey proves which of the two it was.

3. 3 Read the wall, not the log Bondable?

   A resin patch will not bond to a greasy or silted wall, a liner will not lie flat over a root ball, and neither will pass a joint standing proud of the bore.

4. 4 Then choose Patch, line, dig

   Only now is a remedy named, against the run as it stands after cleaning and against the conditions set out at the foot of this page.

Patch lining a single defectLocalised

A patch suits one defect, or two close together, in a pipe that is still round and still on line. The sleeve is cut to length, wetted out, wrapped on the packer, and set to the chainage logged in the survey. It bridges a fracture, seals an open or slightly displaced joint, stops a point of infiltration, and closes the hole a root came through once the root is cut.

What a patch will not do is correct a gradient, re-round a deformed pipe, or hold a length where the host has lost its shape. It also needs an access point close enough to get a packer in, and a run that can be taken out of use for the cure. Where either is missing, the patch comes off the list.

Lining a run end to endFull length

Lining end to end suits a run with defects spread along it, or a run that has to be sealed against infiltration over its whole length. A felt or glass liner is wetted out, inverted or winched in, pressed against the wall and cured, and every lateral that was open before is cut back open from inside afterwards.

Lining also fixes the line it finds. A liner follows the host pipe, so a run laid with a back-fall or a dip keeps both. Those are levels faults, and levels faults are corrected by relaying.

Cutting out and relayingOpen cut

Excavation is the answer when the shape or the position of the pipe is wrong rather than its surface: a collapse, a deformation past re-rounding, a back-fall, a void over the crown, or a connection that has to be made where none exists. It is also the answer when there is no access point to work from.

The hole is set out from the chainage and the measured depth, services are traced and hand-dug to, the sides are battered or supported, and spoil is kept off the dig. The new length is laid to recovered invert levels, bedded and surrounded as the specification requires, tested, and surveyed before the trench is closed. Reinstatement is then its own piece of work with its own standard, in the highway or in a lawn.

Choosing between the threeDecision

The three remedies are not ranked. Each has conditions that rule it in and conditions that rule it out, and the survey is what decides which list a run falls into.