A dimensional line in a tunnel, inside of which rock projections are not permitted

The capability one material has of causing wear of another by rubbing or grinding.

Powder or liquid admixture that accelerates the reaction of cement, especially to shorten the time of setting and increase the rate of early strength development in shotcrete. Different formulations and dosages can be used to regulate the rate of this reaction which, in shotcrete, can achieve initial set in a few minutes or less.

Possibility of gaining entry into a place or system. Possibility of gaining first-hand information. Also, physical point of entry.

Temporary access shafts are commonly provided to allow entry of personnel and occasionally equipment to the interior of an immersed tunnel.

Passage from surface to areas of underground excavation. See also "adit"

Degree of potential for access. Often used relevant to use of physical systems by the disabled. Underground systems may improve or worsen accessibility.

An unplanned incident resulting in personal injury or acute ill health.

Negative alteration of noise level.

Possibility for a tunnelling machine to be adapted to other type of work

A short transverse tunnel connecting two parallel main tunnels; often called a "cross adit"

A short length of horizontal or sub-horizontal tunnel driven from the surface to the main tunnel to enable more headings to be driven or to provide permanent access to the tunnel.

A material added to a concrete or shotcrete mix, which alters the properties of the mix or the final product.

The distance excavated during a given time (shift or day) in tunnelling, drifting, or in raising or sinking a shaft.

Where the tunnel is excavated in sections, a heading within the final cross section, constructed ahead of other parts of the tunnel.

An issue that is considered of value. Only those issues that represent differences among alternatives may be considered in an analysis.

Relating to a visual amenity.

Granular ingredients in concrete or shotcrete such as sand, gravel, crushed stone.

Concrete rail transportating equipment which mixes concrete by rotation of a drum-type car body with helical shaped fins attached to the interior of the car.

A steel cylindrical-shaped vessel with gates for dropping concrete into it and with air connections and discharge pipe connections. After the gun is charged, the concrete is forced through the discharge pipe by air pressure.