Critical Height of Unfilled Zone in Underlying Gob Piles

Table 1

Thickness, burial depth, and lithology of the roof and floor.

Stratum number	Thickness (m)	Buried depth (m)	Lithology	Remarks
7	5.8	138.3	Mudstone
6	2.8	141.1	Sandy mudstone
5	7.8	148.9	Medium sandstone	KS
4	3.5	152.4	No.6 coal seam
3	4.0	156.4	Sandy mudstone
2	9.9	166.3	Fine sandstone	KS
1	8.4	174.7	No. 9 coal seam