短語詞組短語bench h mining 階梯式開采composite -bench mining 組合臺階開采open bench mining 露天臺階式開采overhand bench mining method 上向梯段采礦法grouped bench mining 組合臺階開采underground bench mining 井下梯段采礦法surface bench mining 露天臺階開采high -bench mining 高臺階開采high bench mining 高臺階開采 返回 bench mining