| Term | Definition |
|---|---|
| Heading-and-bench construction |
A tunnelling method in which a top heading is excavated, followed (within one to a few blasts or shoves) by excavation of the lower bench. Distinguished from top heading construction.
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| Heave |
Ground movement in a tunnel in the form of upward deflection of the invert
|
| Heavy ground |
Very incompetent rock, usually found in faults or in shear zones; highly weathered or decomposed material having a tendency to move into the open tunnel area.
|
| Heavy rail |
High capacity rail system with longer trains and heavy rolling stock
|
| Heritage value |
Value in connection with the history or culture of a people and/or place
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| High air |
Compressed air used in tunnels to operate pneumatic tools. Generally supplied at 100 psi.
|
| High pressure grouting |
Consolidation grouting used to strengthen rock or cutt off water inflows.
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| High rock |
A rock surface extending above the invert of a tunnel that would otherwise be driven entirely in soft-ground conditions.
|
| Hog rods |
A steel tumbuckle rod installed horizontally across a shield driven tunnel and fastened on each side to the liner plate, remains in position until the shield tail void is filled with pea gravel and grouted; prevents deflection of the liner plate.
|
| Hoist |
An apparatus for raising rock from a shaft and for lowering and raising men and material. It consists of a load-carrying vehicle attached to the end of a cable or rope usually employing a guideway to stabilize a vehicle.
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| Holing through |
That point in excavation when a tunnel daylights at a portal or meets another face which gives a continuous tunnel.
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| Horseshoe tunnel |
A tunnel of roughly horseshoe-shaped cross section, oriented like an inverted "U". Many variations on the basic configuration are possible.
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| Immersion |
The phase of construction covering the period between the element floating on the surface and installed on its foundation or temporary supports at bed level
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| Impact study |
Study of the influence on the environment of a construction
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| Inbye |
Away from the shaft or portal of a tunnel toward the heading.
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| Inclinometer |
A device for precisely measuring the inclination from vertical of a casing or structure to which the inclinometer is attached. Lateral displacements at specific locations along a common axis are obtained by multiplying the sines of the inclination angles by the distance separating the location at which the measurements are taken.
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| Incompetent ground |
Ground that requires support when a tunnel is excavated through it. Essentially the opposite of competent ground or firm ground. See heavy ground for related definition.
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| Incremental Construction |
A method of construction whereby a short section of an element is constructed, then jacked along to enable the adjacent section to be cast against the previous section.
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| Indirect advantage |
The "indirect advantages" of underground structures are those that are observed in the following alternative options: (1) either do nothing at all, (2) or opt for another type of solution, which does not oblige to build underground, but which meets the expectations of the various concerned "parties" in a less effective way
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| Inert media |
Belonging to non living media.
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