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.

Air-activated, long pipe jacks used for positioning lights drills and maintaining pressure on the drills during the drilling operation. Also known as "feed legs".

Pressure chambers located in the air bulkhead of a tunnel driven under air pressure. Men, material, and equipment pass in and out of the tunnel through these locks. While they are in the locks, the air pressure is slowly adjusted to that will next be encountered in the direction of travel. Separate locks are provided for personnel.

Concrete placing equipment incorporating a pressure vessel with sealing door or valve. Concrete is moved from the vessel to point of placement through the placing pipe by the introduction of compressed air into the vessel.

Chemical contaminants which are released directly into the air by a source or are formed in the atmosphere as a result of secondary chemical reactions

Perforated manifold ring inside the nozzle of wet-mix shotcrete equipment through which high pressure air is introduced into the material flow.

The introduction of compressed air into the concrete pump line or slick line to assist in the placement and compaction of concrete in irregularly shaped openings, such as voids in the tunnel arch or around the flanges of steel tunnel supports.

A crew of miners that is switched from one heading to another in a double-heading location; has the advantage of keeping drilling and mucking operations continuous with one crew of men for each operation.

Different proposals studied in the project phase.

Bar, usually made of steel, used for the stabilization of rock. Placed into a drilled hole and anchored in the rock at the end (end anchorage) or along its whole length (grouted bolt). The visible extremity is often fitted with a plate.

Explosive. A mixture of ammonium nitrate prills and a carbonizing agent.

The configuration of the upper portion of a tunnel section above the springline (crown, roof or back of a tunnel).

All the tunnel lining except the bottom section; also, the process in which this lining is poured; See "invert pour".

Used for limited areas and in certain respects to secure the purposes of the Structure Plan (SP). ARs are binding for private and public

The ratio of length-to-diameter (or equivalent diameter) of the fiber.

These studies take account of three types of effects of a scheme : (1) those which are quantified and valued in terms of money, (2) those which are quantified but not valued, (3) those which are not quantified. It cannot produce a definitive answer; it merely provides information which is relevant to the policy concerns of the decision-maker, in order to illuminate the choice of options.

At or close to the natural ground surface -- not elevated on an embankment or structure, or below ground level in a cutting or tunnel.

Air pollution.

Top of the arch of a tunnel

Filling voids immediately after placing lining