Determination of working resistance of support under different top coal conditions

From the control angle of roof stability in face area, UDEC program has been used in analysis of the relationship between the roof stability in face area, the working resistance of support and the distance to face under different top coal conditions. The results show that the relation curves between working resistance P of support and roof convergence Δ l d in face area are similar to the hyperbola with certain distances to face under soft and medium hard coal conditions, but not under hard coal condition. Hence,methods to calculate of working resistance of support under different top coal conditions are given, and the critical working resistance of support may be determined by P- Δ l d curves under soft and medium hard coal conditions, while traditional method may be used under hard coal condition. The results have been verified by an example.