Maximum empty top distance of the blasting: After the blasting of the working face, the maximum distance of the working face without support is generally determined according to the stability of the rock formation and the supporting row spacing. Under normal circumstances, no more than 2 rows are required.
The maximum empty top distance of the comprehensive excavation: After the completion of one cut of the comprehensive excavator, the maximum empty top distance of the working surface without support is generally 2 times that of the support row.
Cannon excavation, fully excavated minimum empty top distance: refers to the minimum unsupported distance of the working face after support, generally not more than 1/2 of the support rejection.
Basically this is what it means, as if each mine is not uniform. Because there is no regulation in the Coal Mine Safety Regulations.
Textile Printing Reactive Ink,Digital Textile Printing Ink,Textile Printing Reactive Dye Ink,Textile Printing Reactive Fabric Ink
GREEN-LIFE PAPER LTD , https://www.green-lifepaper.com