8.8 Collection System Rehabilitation: CIPP, Pipe Bursting, Sliplining, Grouting, Manhole Repair & Tap Defects
Key Takeaways
- Chemical grouting seals leaking joints but adds no structural strength, so it is the wrong choice when the pipe walls themselves are failing.
- Cured-in-place pipe blinds every lateral connection, so each must be reinstated with a robotic cutter and verified by CCTV before the line returns to service.
- Pipe bursting replaces at the same or larger diameter while sliplining always loses diameter and requires excavating laterals.
- The frame-to-chimney joint is the most common manhole leakage point, and cone and barrel deterioration is usually sulfuric acid attack from hydrogen sulfide.
- Inflow sources such as picked covers, cross connections, and roof and foundation drains give the largest immediate flow reduction for the lowest cost, while infiltration requires lining or replacement over long lengths.
Fixing pipe without digging it up
WPI lists rehabilitating and repairing the collection system — lift stations, manholes (collar, risers, cone, barrel, invert), sewer lines (pipe bursting, pipe lining, pipe repair), taps (top hat, grouting, protruding laterals), and eliminating infiltration, inflow, and exfiltration — as an explicit job task, and separately lists repairing and replacing lines including force mains, combined sewers, sanitary sewers, and storm drains.
Choosing a method
The CCTV inspection and the PACP condition codes determine the method. The question is always the same: is the host pipe structurally sound enough to line, or must it be replaced?
| Method | Description | Best for | Limits |
|---|---|---|---|
| Cured-in-place pipe (CIPP) | Resin-saturated felt or fiberglass liner inverted or winched in, then cured with hot water, steam, or UV light | Structurally deteriorated but round pipe; the workhorse | Reduces diameter slightly; laterals must be reinstated by robotic cutter; styrene and heat handling |
| Sliplining | A smaller-diameter new pipe pushed or pulled inside the old, annulus grouted | Simple, low cost, long runs | Significant diameter loss; laterals must be excavated |
| Pipe bursting | A bursting head fractures the old pipe outward while pulling in new HDPE | Replacement with same or larger diameter | Needs insertion and receiving pits; risks to nearby utilities from ground displacement |
| Fold-and-form / deformed liner | Thermoplastic liner folded, inserted, then reverted to round with heat and pressure | Round pipe, moderate deterioration | Similar constraints to CIPP |
| Spiral wound | Interlocking strip wound in place | Large diameter, live flow | Diameter loss |
| Spot repair / sectional liner | Short liner or point repair at a single defect | Isolated defects | Not a system solution |
| Chemical grouting | Gel injected at a joint or crack through a packer | Leak sealing only, not structural | Does not restore structure; may be temporary |
| Open cut replacement | Excavate and replace | Collapsed pipe, grade problems, upsizing | Cost, traffic, restoration |
The distinction that appears most often on exams: chemical grouting stops leakage but adds no structural strength, while CIPP and pipe bursting restore or replace structure. Grouting a joint in a pipe whose walls are failing solves the wrong problem.
Manhole rehabilitation
Manholes are a large and often underestimated source of inflow and of hydrogen sulfide damage. Components in the WPI list — collar, risers, cone, barrel, invert — each fail differently:
- Frame and cover. A picked or vented cover in a low spot admits enormous stormwater inflow. Solid, gasketed covers and internal inflow dishes are cheap, high-return fixes.
- Frame-to-chimney (collar) joint. The most common leakage point, since traffic loading works the frame against the cone. Repaired with chimney seals of rubber or with cementitious or urethane products.
- Adjusting rings (risers). Deteriorated brick or damaged rings admit water and destabilize the frame.
- Cone and barrel. Concrete attacked by sulfuric acid from hydrogen sulfide, especially above the water line. Repaired by cementitious lining, epoxy or polyurethane coating, or a full liner.
- Invert and bench. Eroded or reshaped inverts cause turbulence, solids deposition, and odor. Rebuilt with grout to restore a smooth channel.
Lateral and tap defects
Taps are listed specifically. Common defects and their fixes:
- Protruding (hammer) tap — a lateral driven too far into the main, catching debris and forming a chronic blockage point. Cut back with a robotic cutter.
- Broken or offset connection — repaired with a top hat or T-liner, a CIPP element that seals the main-to-lateral junction from inside.
- Root intrusion at the connection — cut, then sealed by grouting or a lateral liner, because cutting alone guarantees regrowth.
- After CIPP lining a main, every lateral is blind until it is reinstated by a robotic cutter working from inside the lined pipe. Missing a reinstatement backs up a customer, so reinstatement is verified by CCTV before the line goes back in service.
Eliminating infiltration, inflow, and exfiltration
Rehabilitation only pays if it targets the right defects. Infiltration enters through defective joints, cracks, and lateral connections below the groundwater table; inflow enters directly through manhole covers, cross connections with storm drains, roof and foundation drains, and area drains. Exfiltration is sewage leaking out, which is a groundwater contamination issue rather than a treatment cost.
The practical rule: inflow sources are usually cheaper to fix and yield larger immediate reductions — sealing manhole covers, disconnecting downspouts, correcting cross connections — while infiltration requires lining, grouting, or replacement over long lengths. A sewer system evaluation survey that pairs flow monitoring with smoke testing, dye testing, and CCTV is what ranks the work.
Private property is where much of the flow comes from. Defective laterals, foundation drains, and sump pumps discharging to the sanitary sewer often account for more of the wet-weather response than the public main does, and a rehabilitation program that ignores private-side sources routinely underdelivers.
A CCTV inspection shows a vitrified clay sewer with multiple leaking joints but sound, unbroken pipe walls and correct grade. Chemical grouting is proposed. What is the correct assessment?
After a main is lined with cured-in-place pipe, what must be done before the line returns to service?
In a typical sewer system evaluation survey, which category of defect usually offers the largest immediate flow reduction for the lowest cost?