Costs for an activity or project that are borne by a community

See social costs

Effects arising from social structures or institutional structures and their interaction

A discrete section of shaft lining of lower strebgth designed to be excavated at the start of a tunnel drive from that shaft or the breakthrough of a drive into the shaft

Heavy ground or rock about underground openings that does not stand well and requires heavy timbering

Any tunnel shield which moves forward by reacting (i.e., exerting shove forces) against the tunnel lining and generally utilizing drag type excavation tools that can be mounted on a backhoe, rotating wheel or oscillating arm.

Same as earth tunnel. The ground may be hard or soft in consistency, the word "soft" differentiating it only from "hard" rock.

Any naturally occuring loose or soft deposit resulting from weathering or breakdown of rock formations or from decay of organic matter

Solid products useless that have to be eliminated.

A rail used by mine surveyors for hanging a plumb bob as a mark for a survey station, generally with a hole or notch in it for a plumb bob string.

The breaking off of thin surface sheets or plates in rock under excessive tension.

Part of a structure between two supports

Essentially the same as forepoling, but may also include steel bars drilled ahead of a rock tunnel face.

Related to all kind of oils and liquids of engines that can pollute the soil.

See muck.

A mixture of cement, aggregate, and water projected pneumatically at high velocity from a nozzle onto a surface to produce a layer or layers of concrete. Sprayed concrete normally incorporates admixtures, especially accelerators, and may also include fibers. (See Shotcrete).

Process of placing shotcrete (sprayed concrete) by projecting the shotcrete from the nozzle to the surface receiving the shotcrete (also called shooting or gunning)

see "spring line"

The point where the curved portion of a tunnel roof meets the top of the wall. In a circular tunnel the springlines are at the opposite ends of the horizontal centerline.

The additional draft of a floating body moving relative to the water in which it floats, as compared with the draft when stationary. It is caused by a reduction in water pressure below the body because of directional changes in flow around the body. When keel clearances are marginal, squat may cause elements under tow to touch the bottom. Similarly, an element below a passing vessel may experience uplift due to squat or propeller wash. This may need to be taken into account in selecting safety factors against uplift during installation.