| Term | Definition |
|---|---|
| Deflectometer |
A device for precisely measuring the relative rotation of adjacent line segments along a common axis. The products of the sine of the relative rotation angle and length of line segment are summed by means of double integration techniques to obtain a displacement profile.
|
| Deformation |
A change of shape of a structure or part of a structure or the ground. Usually refers to the change in shape with respect to load and time of the inner profile of the tunnel.
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| Delay |
An enforced wait in an activity. Pertains to value-of-time studies
|
| Delay (blasting) cap/ delay connector |
Exploders used in the tunnel face, that have delay provisions resulting in the charges' firing in rotation. Delay caps are used so that the rock will be exploded into an area into which it can expand.
|
| Demolition permit |
Permission required to demolish buildings within areas with development plans. Permission is obtained by Building Committee
|
| Dense-stream conveying |
A method of conveyance of wet mix from the shotcrete machine by which the wet mix is conveyed through the delivery line without compressed air.
|
| Desanding plant |
Equipment used for treating and eliminating sand of bentonite mud.
|
| Design |
The information required to carry out engineering works
|
| Development plans (DP) |
Zoning plans used to regulate land use and the construction of buildings and facilities in greater detail. DPs are binding for private and public. DPs are adopted by the City Coucil after a legal process
|
| Diamond cut |
Inclined short drill holes near the center of the tunnel face, so arranged that when the first shots are exploded in the round, a diamond-shaped 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.
|
| Diaphragm wall |
Wall built by concreting within a deep and narrow trench the sides of which are held in place by a thixotropic slurry.
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| Diesel smoke |
Carbon particles in suspension, main pollutant element of diesel engines.
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| Digger shield |
A shield with means for rotary mechanical excavation.
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| Direct advantage |
The "direct advantages" of underground structures are those that are observed in comparison with structures built above ground and which have the same purpose, i.e. those that provide the same type of services.
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| Disadvantage |
An issue of detriment or negative value
|
| Disc cutter |
The most common type of roller cutter, taking the form of a single circular disc or cutter blade of hardened steel alloy which revolves freely about its axis as it rolls around the rock face. May carry double or triple disc blades on a single cutter mounting.
|
| Division / Isolation / Separation of communities |
The splitting of existing communities by intrusive and difficult-to-cross infrastructure elements such as at-grade or aboveground roads or rail lines
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| Double heading |
Two headings in a tunnel that can be driven from one plant location. Double headings are possible, for example, when a tunnel passes through and daylights in a depression or canyon or when two headings are driven from one adit.
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| Double heading crew |
Crew of men, located at one entrance to the tunnel, who drive two headings simultaneously from this entrance.
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| Dowel |
Rock reinforcement, usually a reinforcing bar, that is inserted untensioned and fully grouted in place in a borehole.
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