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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Track ballast ： ウィキペディア英語版 Track ballast Track ballast forms the trackbed upon which railway sleepers (UK) or railroad ties (US) are laid. It is packed between, below, and around the ties. It is used to bear the load from the railroad ties, to facilitate drainage of water, and also to keep down vegetation that might interfere with the track structure. This also serves to hold the track in place as the trains roll by. It is typically made of crushed stone, although ballast has sometimes consisted of other, less suitable materials. The term "ballast" comes from a nautical term for the stones used to stabilize a ship. ==Construction== The thickness of a layer of track ballast depends on the size and spacing of the ties, the amount of traffic expected on the line, and various other factors. Track ballast should never be laid down less than thick; high-speed railway lines may require ballast up to thick.〔Bell 2004, p. 396.〕 An insufficient depth of ballast overloads the underlying soil; in the worst cases, this can cause the track to sink.〔Hay 1982, p. 399.〕 If the ballast is less than thick, this can lead to vibrations, which can damage nearby structures (though increasing the depth beyond this has no measurable effect).〔Bachmann 1997, p. 121.〕 Track ballast typically sits on a layer of sub-ballast; the latter is typically made of small crushed stones. It gives a solid support for the top ballast, and seals out water from the underlying ground. Sometimes, an elastic mat is placed under the ballast layer as well; this can allow for significant reductions in vibration.〔 It is essential for ballast to be piled as high as the ties, and for a substantial "shoulder" to be placed at their ends; the latter being especially important, since this ballast shoulder is, for the most part, the only thing restraining lateral movement of the track. The ballast shoulder should be at least wide under any circumstances, and may be as large as . 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Track ballast」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.