Research on Formation Mechanism and Evolution Pattern of Bed Separation Zone during Repeated Mining in Multiple Coal Seams

Table 4

Classification of overburden structure.

Classification	Coal seam structure	Key stratum structure	Key stratum location	Mining condition	Bed separation position
Class I	Single	Single	Above coal seam	Single layer mining	Under the key stratum
Class II	Single	Multiple	Above coal seam	Single layer mining	Under low key stratum
Class III	Multiple	Single	Above coal seam	Mining upper coal	Under the key stratum
			Middle of coal seam	Mining upper coal	Nothing
				Mining lower coal	Under the key stratum
Class IV	Multiple	Multiple	Above coal seam	Mining upper coal	Under low key stratum
				Mining lower coal	Under high key stratum
			Interphase distribution	Mining upper coal	Under high key stratum
				Mining lower coal	Under low key stratum