The International Society for Trenchless Technology

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Term Definition
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.

Contact Grout

A cement or bentonite-cement based mixture injected to fill annular space between pipe and the surrounding formation, or other voids.

Continuous Sliplining

Method of lining with a pipe made continuous for the length of the section to be renovated prior to insertion, and which has not been shaped to give a cross sectional diameter smaller than its final diameter after installation.

Control Console

An electronic unit inside a container located on the surface that controls the operation of the microtunneling machine. Electronic information including head position, steering angle, jacking force, progression rate, machine face torque, slurry and feed pressures, and laser position is transmitted to the console from the head of the machine. The consoles may be equipped with a computer that provides real-time analysis of the tunnel drive.

Conventional Trenching

See Open Cut


Pipeline installation in which the primary purpose is to provide one or more passages beneath a surface obstruction.

Crush Lining

See Pipe Eating.

Cured-In-Place Pipe (CIPP)

Method of lining with a flexible tube impregnated with a thermosetting resin which produces a pipe after resin cure.

Cut and Cover

See Open Cut

Cutter Boom

A mechanical device for excavation within an open shield

Cutting/Cutter Head

Tool or system of tools on a common support which excavates at the face of a bore.


See Spoil

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