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.

Weak material, generally clayed, that behaves plastically under the weight of overlying ground and tends to close a tunnel opening by slowly advancing into it without perceptible volume increse.

The time that elapses between the exposure of an area at the roof of a tunnel and the beginning of noticeable, unprovoked inward movement of the ground above this area; sometimes described as "bridge-action time".

A particular perspective on a problem or issue

(2) Double Shell: An outer steel plate, usually octagonal in shape, is added to a single shell tunnel element to act as an external form plate for tremie concrete placed as permanent ballast. The tremie concrete protects the inner shell plate from corrosion, while the outer form plate is left as sacrificial. Behaviour of the inner shell plate, and the compositely acting reinforced concrete within it, is similar to a single shell tunnel element except that the stiffening elements are usually placed outside the inner shell plate.

(1) Single Shell: Term applied to a tunnel consisting of elements where an outer structural steel membrane (the shell) is constructed first, very much in the manner of a ship. The steel plate also acts as a waterproofing membrane. Elements are usually designed to leave a green field site before the structural concrete is placed, though this may not be the case when other types of fabrication facility are used. Depending upon floating stability requirements, keel concrete may or may not be placed prior to launching. In this condition, draft is usually less than 3 m, making long tows relatively easy while afloat. Nevertheless, transport on barges is not uncommon. The shell plate acts as the exterior form plate for the structural reinforced concrete with which it is designed to act compositely. While stability and strength requirements may require some of the structural concrete to be placed before transportation, it is usual for this concrete to be completed during outfitting, close to the final location. Ballast may be located inside, but more usually outside on top.

Inert material packed in a drilled hole on top of the explosive charge. Its purpose is to contain the force of the explosion in the rock.

Where two tunnels lined with plates of different diameters meet, special vertical plates are required to close the vertical faces - so forming a step. Often in situ concrete is used instead of plates to avoid the heavy cost and time delay in making special plates.

Underground space performed by driving technology

Excessive overbreak occuring for only a short distance and extending to a considerable height above the crown of a tunnel; may also be referred to as a "chimney".

A highly inclined or vertical excavation driven from the main tunnel or drift in an upward direction.

Drills designed for drilling overhead holes.

Deals with land and water use and property development the entire municipality (compulsory in Sweden). SPs are not binding for development plans, more a policy statement adopted by the City Council

Compression supports placed between tunnel sets.

A bulkhead form used in monolithically placed concrete tunnel linings which extends from the tunnel invert to an elevation of sufficient height to ensure a proper seal of the fluid concrete to the invert of the tunnel lining form. Stub bulkheads are utilized in conjunction with unformed sloping construction joints above them. The height of the stub bulkhead can be varied to establish the required length of sloping joint.

A tunnel through water that is not in direct contact with the bed. It may be either positively or negatively buoyant, and may be suspended from the surface, or supported from or tied down to the bed