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Explorer
A term applied to minerals occurring in small quantities in a rock, and whose presence or absence does not affect its mechanical properties.
Chemical term for an igneous rock containing more than 62% silica and usually less than 20% dark minerals. (Contrast with "intermediate" and "basic").
Passage from surface to areas of underground excavation. See also "adit"
Tunnel from surface to underground work site.
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The point in a tunnel or cavern where the wall and roof (back) meet.
CO, CO2 - Carbon monoxide, carbon dioxide. Common pollutants monitored in urban areas. Work has been directed at understanding the total cost to society of the release of such pollutants
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Horizontal compression members, usually timber, placed between adjacent steel rib or timber supports. Collar braces are set in line and tightened with tie rods. If they are made of steel or precast concrete, they need not be removed before pouring concrete lining.
A rail line designed principally to handle commuter trips.
A system by which grout is injected into the ground above a tunnel and below man-made surface features. The intention is to reduce the effects of surface settlement caused by the tunnelling works.