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2 When using the filling method, the reinforced concrete false bottom can be laid at the bottom of the open pit as a false roof for underground mining. When the approach type mining is adopted and the width of the approach is not more than 4m , the thickness of the reinforced concrete false roof should not be less than 1m . When the mining method is used after the empty field, the false concrete thickness of the reinforced concrete should be calculated by rock mechanics according to the span parameter of the stope. determine.
After the end of the open air, the underground mining will be carried out, and the requirements for the retention of the safety safety pillars should be met.
1 When using the open field method for mining, the boundary of the open pit should be set with a safe roof pillar. The thickness of the safety pillar should be determined by rock mechanics, but should not be less than 10m ;