Trenchless technology glossary

A–ZTerms

Access pit

An excavation that gives a crew entry to a pipe for a trenchless method, such as a launch pit for bursting or a pit where no cleanout exists for lining.

Annulus (annular space)

The ring-shaped gap between an old pipe and a new pipe or liner inside it. In slip lining it is normally filled with grout.

Auger boring

A new-path method that jacks a steel casing through the ground from a bore pit while auger flights inside the casing carry the spoil back.

Back reamer

A cutting tool pulled back through a pilot bore in directional drilling to enlarge it for the product pipe, commonly to about 1.5 times the pipe diameter.

Bent sub

A slightly angled section of drill stem behind the head of a directional drill; rotating it sets the direction the head will deflect.

Bentonite

A clay that forms a slick slurry or gel with water, used in drilling fluid to lubricate the bore and hold it open.

Bore pit

The excavation that holds boring or jacking equipment on line and grade. For auger boring it can be about 8 to 12 m long.

Bursting head

A cone-shaped tool pulled or hammered through an old pipe to fracture it and push the pieces outward while new pipe follows.

Bypass pumping

Temporary pumps and hoses that carry sewage around a section of pipe while it is lined, burst or replaced.

Calibration hose

An inner hose inverted inside a pulled-in CIPP liner to press it against the pipe wall before curing.

Carrier pipe

The pipe that actually carries the water, sewage or gas, often installed inside a steel casing at a crossing.

Casing

A sleeve, usually steel, installed by boring, ramming or drilling to protect and house a carrier pipe.

Casing chocks

Spacers fitted to a carrier pipe to centre it in a casing and allow its grade to be adjusted.

CCTV inspection

A closed-circuit camera survey of the inside of a pipe, recorded with distances, used before and after trenchless work.

Close-fit liner

A thermoplastic pipe made in a folded or reduced shape, pulled into an old pipe and expanded tight against its wall with heat and pressure.

Compaction boring

A group of small-bore methods, including push rods and impact moles, that form a hole by displacing soil rather than removing it.

Cover

The depth of soil over the top of a pipe or bore. A rule of thumb for small bores is about one foot of cover per inch of diameter.

Cured-in-place pipe (CIPP)

A liner formed by inserting a resin-saturated tube into a pipe, pressing it against the wall and curing it hard with hot water, steam or UV light.

Deformed-reformed pipe

A close-fit liner that is deformed to a smaller shape for insertion and then restored to round with heat and pressure.

Design life

The service period a product or rehabilitation is designed to achieve, such as the 50-year design life in Toronto's watermain lining specification.

Drilling fluid

Water mixed with bentonite or polymer, pumped to the cutting head in directional drilling to cut, cool, carry cuttings and support the bore.

Duckbill

A slanted steering plate on the front of a small directional drill head.

Epoxy barrier coating

A thin epoxy film applied inside a pipe to stop corrosion and seal pinholes, relying on the pipe for strength.

Exfiltration

Sewage leaking out of a pipe into the surrounding ground.

Fold-and-form pipe

A PVC or polyethylene pipe folded into a U shape at the factory, pulled into an old pipe, then heated and rounded against its wall.

Frac-out

Drilling fluid escaping under pressure from a directional bore to the surface or into a waterway.

Fully deteriorated host

An ASTM F1216 design condition in which the old pipe is assumed to carry no load, so the liner must carry soil, water and traffic loads itself.

Guided boring

Boring methods that use a steered pilot pass, such as pilot-tube systems, to improve line and grade accuracy on small pipes.

Heave

Upward movement of the ground surface caused by soil pushed aside by a bursting head, mole or under-reamed bore.

Host pipe

The existing pipe that is being lined, burst, split or reamed.

Impact mole

A torpedo-shaped pneumatic hammer that drives itself through the soil to make a small bore; it cannot be steered once launched.

Infiltration

Groundwater leaking into a sewer through joints, cracks and manholes. Rehabilitation can reduce it.

Inflow

Stormwater entering a sanitary sewer through improper connections such as downspouts or sump pumps. Lining does little to reduce it.

Insertion pit

The excavation, often a sloped trench, through which a slip liner or burst pipe enters the old pipe.

Intermediate jacking station

A ring of jacks built into a long pipe-jacked or microtunnelled line so it can be pushed in sections.

Inversion

Turning a resin-saturated tube inside out as it is driven into a pipe by water or air pressure, so the resin side ends up against the wall.

Jacking frame

The structure in a jacking shaft that holds the hydraulic cylinders pushing a microtunnelling machine and pipe string.

Jacking pipe

Pipe strong enough to be pushed through the ground from a jacking shaft, such as reinforced concrete, steel or vitrified clay.

Jacking shaft

The deep excavation from which pipe jacking or microtunnelling is launched, with a thrust wall to push against.

Lateral

The service pipe connecting a building's drain to the municipal sewer main. Ownership of it is split differently by each city.

Launch pit

The excavation where a bursting head, mole or rammed casing starts its run.

Maxi-HDD

Large directional drilling for long, large-diameter installations such as river crossings, covered by ASTM F1962.

Microtunnel boring machine (MTBM)

The remote-controlled, laser-guided machine at the front of a microtunnel drive that cuts the face and is pushed by the pipe behind it.

Microtunnelling

Remote-controlled, laser-guided pipe jacking with continuous face support, used for sewers that must hold grade closely.

Mini-HDD

Small directional drilling with compact rigs, for pipes up to about 10 inches over shorter bores.

Open cut

Installing or replacing a pipe by digging a trench along its whole length.

Partially deteriorated host

An ASTM F1216 design condition in which the old pipe still carries the soil and traffic loads and the liner mainly resists groundwater and bridges defects.

Pilot bore

The first, usually steered, pass of a directional or guided bore, later enlarged by reaming.

Pipe bursting

Replacing a brittle pipe by breaking it outward with a head while new pipe of the same or larger size is pulled in behind.

Pipe eating

A microtunnelling-based replacement method that crushes an old sewer and removes it through the new pipeline, allowing grade adjustment.

Pipe ejection

Replacing a pipe by jacking new sections against it so the old pipe is pushed out into the reception pit.

Pipe jacking

Pushing a string of strong pipes through the ground from a jacking shaft while the face is excavated inside a shield.

Pipe ramming

Hammering an open-ended steel casing through the ground with a pneumatic tool, then clearing out the soil core.

Pipe reaming

Replacing a non-metallic pipe by pulling a reaming head through it on a drill string, grinding it up and flushing the pieces out in slurry.

Pipe splitting

Replacing a tough pipe such as ductile iron, steel or plastic by slicing it open with cutting wheels and a blade and spreading it apart.

Pullback

The final stage of directional drilling, when the product pipe is pulled into the reamed bore.

Reception shaft

The excavation where a microtunnelling machine or jacked pipe arrives at the end of a drive.

Reinstatement

Reopening branch connections from inside a newly lined pipe, usually with a remote-controlled cutter.

Relaxation

The slow shrink-back of polyethylene pipe after it has been stretched by pulling; services are reconnected only after it has relaxed.

Segmental slip lining

Slip lining with short rigid sections pushed into the old pipe one at a time from a small pit.

Slip lining

Inserting a smaller finished pipe into an old one and normally grouting the annulus.

Sonde

A radio transmitter behind a drill or camera head, tracked from the surface to find position and depth.

Spiral-wound liner

A liner formed inside an old pipe by winding a plastic profile strip into a continuous pipe.

Static pull

Bursting or splitting in which the breaking force comes only from pulling the head, often with rods.

Styrene

A component of many sewer relining resins that gives a glue-like odour during curing.

Tolerance

The allowed deviation from the designed line and grade of a bore or pipe.

Trenchless

Renewing, replacing or installing underground pipe from access points instead of a continuous trench.

UV curing

Hardening a light-reactive resin liner by pulling a train of ultraviolet lamps through it.

Walkover locator

A handheld receiver carried over the ground to read a sonde and track a drill or camera head.