短語詞組短語rock bench excavation 巖臺開挖heading and bench excavation 導(dǎo)洞與臺階開挖top heading and bench excavation 上下臺階開挖Tri -bench excavation method 三臺階開挖法three -bench seven-step excavation method 三臺階七步開挖法 返回 bench excavation