在卡拉冈达煤田,由于在工作面上难冒落顶板的周期性沉降和经常性的冒落(一年之中有4～7次此类事故),使有此种顶板煤层的开采工作复杂起来。同岩层顶板的较易冒落的采面相比较,这些回采工作面的平均产量降低40％,劳动生产率降低60％,因而吨煤成本提高了30％。为了在难冒落顶板的条件下有效地进行回采工作,必须根据煤 In the Kalangada coalfield, the mining of such roof coal seams is complicated by the periodic settlement and frequent collapse of roofs that are not easily found on the work surface (four to seven such incidents a year) stand up. Compared with the more prone roofs in the rock roof, the average production of these working faces is reduced by 40% and the labor productivity is reduced by 60%. As a result, the cost per tonne of coal is increased by 30%. In order to effectively refrain from falling roof conditions for mining work must be based on coal