underground air矿内空气undergroundadj.地下的；秘密的adv.在地下；秘密地n.地下；地铁；地道；秘密活动underground openings and tunnels地下洞室群underground pressure observation矿压观测Underground pipelines and cables地下管线underground big-space building地下大型建筑underground artificial structure地下人工结构underground engineering envelope地下工程围护结构underground hot-water features地下热水特征underground mining from open pit露天转地下开采underground coal mine environment煤矿井下环境underground chisel rock equipment地下凿岩设备