Trenchless pipe repair: five methods, and the defect decides which one

Why the method follows the defect

Every trenchless method solves a specific class of problem. Choosing among them by contractor preference, or by whichever one the first company to answer the phone happens to sell, is how a project ends up with a technically sound installation that does not address the actual fault.

Five methods cover the great majority of work in gravity pipes and building drains. What follows is what each one does, and, more usefully, what disqualifies it.

Full-length lining

A continuous liner installed along the whole run between two access points, curing into a jointless pipe inside the old one.

• Fits: pipes with distributed defects, multiple cracks, several open joints, general corrosion, widespread root intrusion.
• Rules it out: collapse, sag, severe deformation, a missing section, or a need for greater capacity.
• Watch: the number of laterals, the geometry of the run and the access available at each end.

The method, its conditions and its documentation are covered on the CIPP lining page.

Sectional and point repairs

A short liner installed across a single defect, a cracked joint, a localized fracture, rather than along the full length. It is placed on a packer, positioned against the defect, expanded and cured.

• Fits: an isolated defect in a pipe that is otherwise in serviceable condition.
• Rules it out: a run with defects every few feet, where a series of point repairs costs more than lining the whole thing and leaves every untreated joint as a future call-out.
• Watch: the honesty of the survey. A point repair on a pipe that needed full lining is the most common way to spend money twice.

Pipe bursting

Replacement rather than repair, carried out without a continuous trench: a bursting head is drawn through the old pipe, fracturing it outward into the surrounding soil while pulling a new pipe, usually fused HDPE, into the space it occupied.

• Fits: pipes too far gone to line, and situations where more capacity is needed, bursting can install a larger pipe than the one it destroys.
• Rules it out: proximity of other buried utilities, ground conditions that will not accept the displacement, and some host materials.
• Watch: it needs entry and exit pits, so it is trenchless along the run but not at the ends.

Bursting is the honest answer when someone asks whether a collapsed line can be lined. It cannot, but it may not need a trench either.

Slip lining

A new, smaller pipe is inserted inside the old one and the annular space between them is grouted. Mechanically simple, long established, and undemanding of the host pipe.

• Fits: large-diameter lines where losing some cross-section is acceptable, and hosts too irregular for a close-fit liner.
• Rules it out: any line already close to its hydraulic capacity, the diameter loss here is real and is not compensated by smoothness.
• Watch: lateral connections have to be re-established by excavation in many configurations, which erodes the trenchless advantage.

Spray-applied and cast-in-place linings

A cementitious, geopolymer or resin coating applied to the inside of the pipe by a spinning head drawn along it, building up a wall of specified thickness against the host.

• Fits: manholes, large-diameter structures and pipes with geometry a tube cannot follow.
• Rules it out: small diameters, and applications where a structural liner designed to a recognized standard is required and the coating is not one.
• Watch: whether the product is specified as structural, semi-structural or protective. The three are different purchases, and the words are used loosely in sales conversations.

Grouting

Chemical grout injected at a joint or through a defect to stop water moving through it. It seals; it does not add structure.

• Fits: infiltration control on a structurally sound pipe, typically as part of a wider program.
• Rules it out: any pipe whose wall has lost strength, sealing a joint on a failing pipe treats the symptom that was easiest to see.
• Watch: whether it is being proposed as a cheaper alternative to lining. Sometimes it genuinely is the right scope. Sometimes it is a way to make a bid look competitive.

And the case for opening the ground

Excavation is the method every trenchless page is written against, which makes it easy to forget that it is sometimes simply correct. A short run under an unlandscaped yard, a pipe at shallow depth with a single break, a line that has to be re-graded anyway: on those jobs, digging is faster, cheaper and more certain.

The comparison that actually matters is not trenchless against open-cut in the abstract. It is the total cost of each approach on this pipe, in this ground, under this building, which is what lining or replacement works through.

Frequently asked