19.3 Trenchless Rehabilitation: CIPP, Pipe Bursting & Lining
Key Takeaways
- Cured-in-place pipe installs a resin-saturated liner that is inverted or pulled into the host pipe and cured, forming a new pipe within the old one.
- CIPP slightly reduces diameter but usually increases flow capacity because the new liner is far smoother than the deteriorated host pipe.
- Pipe bursting fractures the existing pipe outward and pulls a new pipe into the void, and it is the only trenchless method that can increase diameter.
- Service laterals must be reinstated after lining, typically by a robotic cutter that reopens each connection from inside the new liner.
- Sliplining is the simplest method but reduces diameter the most, and the annular space between the liner and host pipe must be grouted.
19.3 Trenchless Rehabilitation: CIPP, Pipe Bursting & Lining
Trenchless rehabilitation renews a buried pipe with little or no open excavation. In developed areas the cost of open-cut replacement is dominated not by the pipe but by pavement, traffic control, utility conflicts, and disruption, which is why trenchless methods now handle the majority of collection system renewal.
Cured-in-Place Pipe (CIPP)
The dominant method. A flexible tube saturated with thermosetting resin is installed into the host pipe and cured in place, forming a new structural pipe inside the old one with no joints.
Installation:
- Inversion: the liner is turned inside out by water or air pressure, progressively pressing the resin against the host pipe wall.
- Pull-in-place: the liner is winched into position and then inflated against the wall.
Curing:
| Method | Description |
|---|---|
| Hot water | Circulated through the liner; slow, well established |
| Steam | Faster than hot water; less water to handle |
| Ultraviolet (UV) | A UV light train is drawn through a glass-fiber liner; fastest, most controlled, and no heated water to dispose of |
| Ambient | Small-diameter and lateral liners |
Advantages: no excavation except at access points, no joints (which eliminates the root and infiltration pathway), conforms around bends, structural or semi-structural design as required, and long service life.
[!IMPORTANT] CIPP reduces the internal diameter slightly but usually increases hydraulic capacity. The liner is very smooth — a Manning's n around 0.010 compared with 0.013 or worse for deteriorated concrete or tuberculated pipe — and that reduction in roughness generally more than offsets the small loss in area. Candidates often assume lining must reduce capacity; the opposite is normally true.
Considerations: the line must be cleaned and CCTV-inspected first; flow must be bypassed during installation and curing; service laterals are covered by the liner and must be reinstated; and resin styrene odors require public notification and management.
Lateral Reinstatement
After curing, every service connection is buried behind the new liner. A robotic cutter is driven into the lined pipe, locates each lateral from the pre-lining CCTV record, and cuts the connection open. Missing or misaligning a reinstatement backs up a customer's service, so the pre-lining inspection footage log is essential.
Tap and Lateral Connection Repair
Service connections are the weakest point in a rehabilitated sewer, and the Need-to-Know Criteria list taps as their own repair category. Three defects dominate:
| Tap defect | What CCTV shows | Repair |
|---|---|---|
| Protruding lateral | The lateral pipe intrudes into the mainline bore, snagging rags and debris and catching jetting nozzles | Trim flush with a robotic cutter before any lining work |
| Leaking or offset tap | Infiltration running from the connection during a wet-weather inspection | Chemical grouting injected through a packer to seal the annulus around the tap |
| Unsealed connection after lining | Water tracking behind the liner at the reinstated cut | A top hat (also called a T-liner) — a short brimmed, resin-impregnated sleeve set into the lateral with the brim pressed against the mainline liner, curing into a one-piece hydraulic seal |
A top hat is installed after reinstatement, and it is the standard way to keep an otherwise sound CIPP job from leaking at the very connections the robotic cutter just reopened. Protruding laterals must be trimmed before lining: a protrusion left in place telegraphs through the new liner and becomes a permanent debris trap that will generate repeat blockage calls.
Other Trenchless Methods
| Method | Description | Diameter effect |
|---|---|---|
| Sliplining | A smaller new pipe (usually HDPE) is pushed or pulled through the host pipe; the annular space is grouted | Greatest diameter reduction |
| Fold-and-form | A folded thermoplastic liner is inserted, then heated and pressurized to round out against the host pipe | Modest reduction |
| Spiral wound | Interlocking profile strip wound into a new pipe in place | Modest reduction |
| Spray-applied lining | Cementitious or polymer coating spun onto the pipe wall | Minimal |
| Pipe bursting | A bursting head fractures the host pipe outward while pulling a new pipe into the void | Same or LARGER diameter |
| Point/spot repair | A short liner sleeve or packer applied at one defect | Localized |
| Chemical grouting | Grout injected at a leaking joint from inside | Stops infiltration; not structural |
Pipe Bursting
A conical bursting head is pulled through the existing pipe by a winch cable or hydraulic rod string. It splits the host pipe and forces the fragments into the surrounding soil while simultaneously pulling in a new fused HDPE pipe behind it.
[!IMPORTANT] Pipe bursting is the only trenchless method that can increase pipe diameter, which makes it the answer whenever the question involves both deteriorated pipe and insufficient capacity. Its constraints are equally testable: it displaces soil outward, so nearby utilities, building foundations, and shallow cover are at risk; it works on brittle host pipe (vitrified clay, concrete, cast iron) but not readily on ductile materials such as steel; and it requires insertion and receiving pits.
Chemical Grouting
Grout injected through a packer at a joint fills the void in the surrounding soil and seals the leak. It is genuinely effective at stopping infiltration at joints, but it adds no structural strength — a cracked pipe that is grouted is still a cracked pipe.
Manhole Rehabilitation
Manholes are a disproportionate share of both inflow and hydrogen sulfide damage, and they are cheap to fix relative to pipe.
| Defect | Rehabilitation |
|---|---|
| Frame and cover leakage | Reseal frame, install a chimney seal, replace with a sealed and gasketed cover |
| Chimney and corbel deterioration | Chimney seal, cementitious or epoxy lining |
| Barrel and joint infiltration | Chemical grouting, cementitious lining, epoxy or polyurethane coating |
| H₂S corrosion of concrete | Epoxy, polyurethane, or calcium aluminate lining; cementitious repair mortar |
| Bench and invert damage | Rebuild with repair mortar |
| Inflow through a vented cover | Solid sealed cover, or an internal inflow dish or dish insert |
Inflow dishes are inexpensive inserts that sit under the cover and catch surface water entering through the pick holes and the frame seat. In a system with hundreds of manholes in ponding streets, they are among the highest-return inflow reduction measures available.
Bypass Pumping and Flow Control
Every rehabilitation method requires the line to be taken out of service, which means the flow must go somewhere.
- Plugging with inflatable or mechanical plugs upstream, with pressure monitoring on the plugged reach.
- Bypass pumping around the work area using pumps and temporary discharge piping sized for peak rather than average flow.
- Redundancy: a standby pump and a plan for pump failure, because a bypass failure during a peak period causes an overflow.
- Continuous attendance or monitored alarms while a bypass is running.
[!WARNING] Plugging a live sewer is one of the most hazardous routine tasks in collection work. A plug that fails or is dislodged under a surcharged head releases a violent flow that can kill a worker in the manhole. Plugs must be properly sized, restrained against blowout, and continuously monitored, and the upstream surcharge level must be watched. Never enter a manhole downstream of a plug holding back a surcharged line.
Selecting a Method
| Situation | Typical choice |
|---|---|
| Structurally deteriorated, capacity adequate | CIPP |
| Deteriorated and undersized | Pipe bursting |
| One isolated defect | Spot repair |
| Joint infiltration, pipe otherwise sound | Chemical grouting |
| Severe H₂S corrosion in large diameter | Spray-applied or CIPP structural liner |
| Collapsed pipe, no continuous bore | Open-cut replacement |
That last row matters: trenchless methods require a continuous, navigable host pipe. A fully collapsed line cannot be lined or burst, because there is nothing to pull through.
A 12-inch vitrified clay sewer is structurally deteriorated and also surcharges during wet weather because it lacks capacity. Which rehabilitation method addresses both problems?
After CIPP lining a reach, what must be done before the line is returned to service, and why is the pre-lining CCTV record essential?
Why is CIPP lining generally expected to maintain or increase hydraulic capacity despite reducing the internal diameter?