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Definition of shield

i. A framework or diaphragm of steel, iron, or wood, used in tunneling and mining in unconsolidated materials. It is moved forward at the end of the tunnel or adit in process of excavation, and is used to support the ground ahead of the lining and to aid in its construction.

Ref: AGI

ii. A large area of exposed basement rocks in a craton, commonly with a very gently convex surface, surrounded by sediment-covered platforms; e.g., Canadian Shield, Baltic Shield. The rocks of virtually all shield areas are Precambrian.

Synonym of: continental shield, cratogene, continental nucleus

Ref: AGI

iii. In longwall mining, the hydraulically powered roof supports that protect the face workers and advance as the panel is extracted.

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