英语翻译

题目

英语翻译
when the enemy is over the mine the touch of an electric button causes it to spring out of the ground until it is checked by a chain at the height of a yard above the surface,when it explodes,mowing down every man in the vicinity.
请完整翻译整个句子,第一句话好理解：“敌人走到地雷上,触发了电动按钮就会使地雷炸出地面,.地雷爆炸会撂倒每个在附近的敌人”最关键的是until it is checked by a chain at the height of a yard above the surface 这句话如何译呢?

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