bottom slicing meaning in English

上行分层开采法

Rapid excavation technology applied in conveyer gateway of bottom slicing coal mining face
下分层工作面运输巷快速掘进施工技术
Combined support of crossing point of roadway bottom slice and loose rock stratum with rockbolt net and bamboo curtain
底分层及松散岩层巷道交叉点锚网竹笆联合支护的研究
Study and practice of bottom slicing relieving mining in condition of trouble coal seams with high ground stress under deep coal mine
深井高应力难采煤层上行卸压开采的研究与实践