Table 2 Calculation Results of Key Layers Overlying the 12,240 Working Face and Instability Scale.

From: Overlying strata movement law and rockburst prevention & control for fully mechanized top coal caving face in extra-thick coal seams

Horizon

Lithology

Hard rock type

Thickness/m

Distance from

2–3 coal seam roof/m

Initial instability scale/m

Periodic instability scale/m

Y13

Fine sandstone

Medium hard rock stratum 3

13.45

47.64

56.66

23.13

Y10

Fine sandstone

Medium hard rock stratum 2

9.25

27.39

55.96

22.84

Y8

Medium sandstone

Medium hard rock stratum 1

5.25

16.79

49.17

20.07

Y2

Medium sandstone

Low-lying hard rock stratum

2.65

2.69

20.25

8.27

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