The International Society for Trenchless Technology

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Term Definition

A principal module of a shield microtunneling or tunnel-boring machine (TBM). Trailing cans may be used to faciliate steering. It may also be referred to as a trailing tube.

Carrier Pipe

Pipe to be rehabilitated by any trenchless rehabilitation method.

Cased Bore

Bore in which a pipe, usually a steel sleeve, is inserted simultaneously with the boring operation. Usually associated with auger boring or pipe jacking.


A pipe to support the bore. Usually not the product pipe.


General trenchless technology term that refers to methods for closing joints within a pipeline or between lining segments.

Cement Mortar Liners

Spray-on coating used primarily for corrosion protection of small diameter metal pipelines. Cement mortar and concrete linings can also provide structural and leak protection benefits in larger man-entry pipes or tunnels.

Chemical Grouting

Method for the treatment of the ground around a shaft or pipeline, using non-cementitious compounds, to facilitate or make possible the installation of an underground structure.

Chemical Stabilisation

Renovation method which seals a length of pipeline between two access points by employing a chemical solution pumped into the pipe and surrounding ground. Such systems perform a variety of functions including sealing of cracks and cavities, the provision of a new wall surface with improved hydraulic characteristics or ground stabilisation.

Cleaning Systems

A system of centrifugal pumps, tanks with baffles, shakers screens, de-sanding and de-silting hydro cyclones for the removal of cuttings from the slurry for recycling and reuse.

Close-Fit Sliplining

Method of lining with a continuous pipe for which the cross section is reduced to facilitate installation, and reverted after installation to provide a close fit to the existing pipe.

Closed Circuit Television (CCTV)

Video cameras mounted on small tractor devices or sleds and driven or pulled through a pipeline commonly used to inspect repairs and to assess the condition of the pipe.

Closed Shield

A shield with a closed pressure chamber or cutting head which does not allow direct access to the face.

Compression Ring

A ring fitted between the end-bearing area of the bell and spigot to help distribute applied loads more uniformally. The compression ring is attached to the trailing end of each pipe and is compressed between the pipe sections during jacking. The compression rings compensate for slight misalignment, pipe ends that are not perfectly square, gradual steering corrections, and other pipe irregularities.

Condition Assessment

Methods for identifying and locating features that may affect the integrity and performance of a utility including defects, obstructions, leaks, infiltration, inflow, etc.

Conductor Casing

Steel casing hammered or pushed into place where soil strata are high in gravel and cobble content or where formation strength is low and the bore would be unstable.

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