1 Open-pit mines with large lengths or sub-area mining shall adopt a transitional plan of division and phased when transferring to underground mining;
2 The thickness of the boundary safety pillar or rock cushion should be determined according to the mining method selected;
3 When designing the drainage scheme, the interception and drainage capacity of the original open pit and its influence on the drainage in the pit should be analyzed and studied;
4 The mine should be able to maintain normal production and the total supply of ore is basically balanced;
5 The choice of underground mining methods should be analyzed to study the stability of open slope and the impact of debris flow on underground mining;
6 The mining sequence should be arranged reasonably, and the open and underground mining sites should be staggered at the water level.
During the transition period from open-pit to underground mining, in the lower part of the open-air protection section, when the conditions permit, the underground mining method can adopt the natural caving method, but the subside caving method without the bottom column, the sub-collapse method with the bottom column and other caving methods should not be adopted. When mining by natural caving method, high-stage mining should be adopted. At the same time, the specification of the boundary safety pillar between the open pit and the collapsed roof should be determined by calculation. When the top line of the caving area is near the boundary safety pillar, open-pit mining should be ended or stop.
2 The thickness of the boundary safety pillar or rock cushion should be determined according to the mining method selected;
3 When designing the drainage scheme, the interception and drainage capacity of the original open pit and its influence on the drainage in the pit should be analyzed and studied;
4 The mine should be able to maintain normal production and the total supply of ore is basically balanced;
5 The choice of underground mining methods should be analyzed to study the stability of open slope and the impact of debris flow on underground mining;
6 The mining sequence should be arranged reasonably, and the open and underground mining sites should be staggered at the water level.
During the transition period from open-pit to underground mining, in the lower part of the open-air protection section, when the conditions permit, the underground mining method can adopt the natural caving method, but the subside caving method without the bottom column, the sub-collapse method with the bottom column and other caving methods should not be adopted. When mining by natural caving method, high-stage mining should be adopted. At the same time, the specification of the boundary safety pillar between the open pit and the collapsed roof should be determined by calculation. When the top line of the caving area is near the boundary safety pillar, open-pit mining should be ended or stop.
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