Any frame capable of lifting a car vertically so a train may pass beneath it; used for passing cars.

Assistant to the driller. (Before the use of modern jibs, the driller's assistant had to help position the drill steel while starting the hole in the face; hence the term "chuck tender").

Usually the highest point of the floor on which or against which the gate rests, and over which elements must pass during removal from the fabrication facility.

A tunnel of circular cross section, generally made with a full circular shield or tunnel boring machine.

Protection of the civilian population against the effects of bombs, fallout, and chemical releases

The operation of removing loose muck, water, and other material from a tunnel prior to concreting.

A shield modified for use in subaqueous tunnels in which the working pockets can be closed when "shoving blind".

See Joint, closure.

Maximum admissible limit of pollution produced by Carbon Monoxide.

Carbon monoxide, carbon dioxide. Common pollutants monitored in urban areas. Work has been directed at understanding the total cost to society of the release of such pollutants

Lagging placed tightly between the webs of adjacent ribs.

A watertight enclosure from which the water is pumped to expose the excavation bottom and permit work to be performed there.

Horizontal compression members, usually timber, placed between adjacent steel rib or timber supports. Collar braces are set in line and tightened with tie rods. If they are made of steel or precast concrete, they need not be removed before pouring concrete lining.

A person traveling to and from work

A rail line designed principally to handle commuter trips

A system by which grout is injected into the ground above a tunnel and below man-made surface features. The intention is to reduce the effects of surface settlement caused by the tunnelling works.

A measure of its capacity to resist deformation under load

Rock / ground that can stand for relatively long periods with no support or only minimal support when a tunnel is excavated through it.

Air supplied to the tunnel at greater than atmospheric pressure, either to operate pneumatic tools or to facilitate tunnelling in very soft or wet ground. See also high air or low air.

In general, the granting of a favor or a point during negotiations. In business terms, can represent a contract allowing the building and/or operation of a facility by another company.