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interconnected mass of saltwater covering 70.78% of the surface of the earth, often called the world ocean. It is subdivided into four (or five) major units that are separated from each other in most cases by the continental masses. See also oceanography.
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in mining, an open excavation in the ground. A trench has a trapezoidal cross section, and its length is many times greater than its width.
Sloping main, or primary, trenches are used in stripping an opencut mine or an individual area of such a mine, and also in establishing a haulage system to link the working levels with the surface. A horizontal, or cross-sectional, trench is designed to establish the initial working front at a bench. In the case of irregular mountain terrain, a trench may have an irregular cross section (hasty trench).
Main trenches are classified on various bases. In terms of their relationship to the contours of the pit, they may be external or internal. They may be of the individual type (providing haulage for a single level), the group type (serving several levels), or the general type (for all working levels in the pit). On the basis of the traffic flow, they are classified as single trenches, with two-way traffic, and paired trenches, with one-way traffic.
The width of a horizontal trench depends on the location of the haulage system and excavation equipment in the horizon being stripped. The depth of a horizontal trench corresponds to the height of the horizon to be stripped. The optimum depth of an inclined main external trench is 50–60 m.
In pits with soft rock, trenches are excavated using multibucket excavators, dragline excavators, or scrapers; single-bucket excavators (trenchers) are used in pits with hard rock. Ejection explosions may be used in digging a trench. If conditions permit, the stripped rock is placed on the surface on one or both sides of the trench; otherwise, it is moved by vehicles to spoil banks.
The rate of excavation of trenches depends largely on the time required for construction of the pit and, in sloped and steeply inclined deposits, also on the productivity of the pit.
Trenches are also used in construction, for the laying of pipelines and cables.
IU. I. ANISTRATOV