An underground power station is a type of constructed by excavating the major components (e.g. machine hall, penstocks, and tailrace) from rock, rather than the more common surface-based construction methods. One or more conditions impact whether a power station is constructed underg.
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The islands of Tuvalu are narrow atolls composed of coral, so a football field could only be located at the broadest part of the main island of . The football field on Tuvalu is built on a base, with river clay shipped in from to create a surface on which grass has grown. This improved the football field's condition, although the surface remains hard and is not uniformly flat.
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