| Term | Definition |
|---|---|
| Diesel smoke |
Carbon particles in suspension, main pollutant element of diesel engines.
|
| Digger shield |
A shield with means for rotary mechanical excavation.
|
| 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.
|
| 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
|
| 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.
|
| Double heading crew |
Crew of men, located at one entrance to the tunnel, who drive two headings simultaneously from this entrance.
|
| Dowel |
Rock reinforcement, usually a reinforcing bar, that is inserted untensioned and fully grouted in place in a borehole.
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| Draft |
The depth below the still-water surface of the deepest part of a floating body.
|
| Drawback |
See disadvantage
|
| Dredging |
The operation of excavating the trench for an immersed tunnel
|
| Drift |
A mined passageway or portion of a tunnel. In the latter sense, depending upon its location in the final tunnel cross section, it may be classified as a "crown drift", "side drift", "invert drift", etc.
|
| Drifter |
A heavy drill for drilling nearly horizontal holes in the tunnel face. Drifters require support from jibs.
|
| Drill |
In reference to construction operations, the making of a relatively small circular hole in earth or rock with a cutting tool, while removing the cuttings by means of a circulating fluid. Distinguished from bore.
|
| Drill and blast |
A method of desintegrating rock by drilling small diameter holes on a planned layout, packing these with explosives and then firing to a fixed program to shatter the rock in a desired form.
|
| Drill jumbo |
Movable frame on which drill positioners, jibs and drills are mounted.
|
| Drill jumbo |
In drill-and-blast tunnel construction, a rubber-tyred or track mounted movable frame with platforms to support men and drills.
|
| Drill positioners |
Mechanical control for moving, rotating and controlling jibs.
|
| Drill-and-blast |
A method of excavating rock by drilling small-diameter holes on a planned layout, packing these with explosives, and then firing to a fixed program to shatter the rock in a desired form. Distinguished from machine mining, mechanical excavation.
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