Inclined short drill holes near the center of the tunnel face, drilled so that when the first shots are exploded in the round, a wedge of rock is removed, which allows relief for the remaining rock when the delay exploders set off the charges in the other drill holes.

Maximum price that would be paid to obtain a good. It is generally a function of the quantity of this good already possessed or already consumed

A monetary value assigned to loss of life for use in comparative analyses of the cost effectiveness of design options with different safety implications

A monetary value assigned to time saved or lost by users of a transportation system. This may be calculated to vary by anticipated user or user activity when delayed, e.g. business use versus recreational use

Large-diameter pipe used to furnished fresh air or exhaust polluted air from an underground opening

The provision of air circulation/fresh air to an enclosed space. This can provide cost implications when comparing underground and surface solutions

A system in which fresh air is supplied at one end of the tunnel and the polluted air is expelled at the other

A system in which a separate ventilation duct is used for the supply of fresh air through many supply vents along the tunnel. The polluted air is discharged through the end of the tunnel. Also used to describe a system where fresh air is supplied from the end of the tunnel and polluted air is drawn out over the length of the tunnel by exhaust fans

A system in which separate supply and exhaust duct systems are used, so that fresh air is distributed and polluted is collected over the length of the tunnel by supply and exhaust fans

Pipeline used to ventilate the tunnel, eliminating polluted air.

An unwanted change in appearance. Damage over the environment caused by the degradation of the landscape or the loss of visual conditions.

Any wedge-shaped piece of which an arch or vault is composed, or assumed to be composed for purposes of analysis. The center voussoir is keystone.