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 water of mining pit矿坑地下水underground traverse adjustment地下导线线测量underground blast hole drilling井下炮眼钻凿underground water power station地下电站underground locomotive for mine矿用井下电机车underground maintenance vehicle井下维修车underground fracture connection井底裂缝连通underground engineering station地铁工程Underground heat storage system地下蓄热系统underground pipe draining water暗管排水