一、问题的提出我国煤矿一般是采用下行顺序开采煤层群的,这样在下部煤层开采时要为上部煤层的主要巷道留设保安煤柱,如我矿东四尺井12号煤层为上部3号煤层主巷留的保安煤柱储量约78万吨,占全层工业储量的7％。当上部煤层开采后老塘积水时,要开采下部煤层一般必须进行采前疏放, First, the issue raised China's coal mines are generally the order of the coal seam mining down the order, so that the lower part of the coal seams to be set up for the main roadway in the upper coal seams security pillars, such as mine, The coal pillar reserves of the security coal reserves of about 780,000 tons, accounting for 7% of total industrial reserves. When the upper coal seam after the accumulation of Laotang coal mining to the lower part of the general must be pre-mining dredging,